Gr10-Via-Afrika-Physical-Science-Gr10-Study-Guide_LR.pdf

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Via Afrika Physical Sciences Grade 10 Teacher’s Guide What’s rewarding to me is to see my learners performing well. It makes your heart feel so glad and great, and you really feel you’ve achieved something Grade 10 Study Guide when you get your learners on the road to success. D.B. Gibbon, R. Jones, J.E. Patrick, M. Patrick, S.T. Townsend, — Adam Joseph, Teacher T. van Niekerk, T.E. Luvhimbi, N.P. Mlobeli Via Afrika understands, values and supports your role as a teacher. You have the most important job in education, and we Via Afrika Physical Sciences realise that your responsibilities involve far more than just teaching. We have done our utmost to save you time and make your life easier, and we are very proud to be able to help you teach this subject successfully. Here are just some of the things we have done to assist you in this brand-new course: 1. The series was written to be aligned with CAPS. See page 39 to see how CAPS requirements are met. 2. A possible work schedule has been included. See page 7+8 to see how much time this could save you. 3. Each topic starts with an overview of what is taught, and the resources you need. See page 23 to find out how this will help with your planning. 4. There is advice on pace-setting to assist you in completing all the work for the year on time. Page 24 shows you how this is done. 5. Advice on how to introduce concepts and scaffold learning is given for every topic. See page 9+25 for an example. 6. All the answers have been given to save you time doing the exercises yourself. See page 26 for an example. 7. Also included are a full-colour poster and a CD filled with resources to assist you in your teaching and assessment. See the inside front cover. 8. A question bank with tests you may photocopy will help you assess your learners effectively. See the Question Bank on page XX. The accompanying Learner’s Book is written in accessible language and contains all the content your learners need to master. The exciting design and layout will keep their interest and make teaching a pleasure for you. We would love to hear your feedback. Why not tell us how it’s going by emailing us at [email protected]? Alternatively, visit our teacher forum at www.viaafrika.com. Language: English www.viaafrika.com D.B. Gibbon R. Jones J.E. Patrick M. Patrick S.T. Townsend T. van Niekerk Study Guide Via Afrika Physical Science Grade 10 Contents Revision.............................................................................................................. 3 How to use this study guide.................................................................................. 5 Topic 1 Matter and materials.............................................................................. 7 Overview............................................................................................................ 7 Questions..........................................................................................................18 Answers to questions..........................................................................................25 Topic 2 Waves, sound and light........................................................................ 29 Overview.......................................................................................................... 29 Questions..........................................................................................................35 Answers to questions......................................................................................... 46 Topic 3 Magnetism and electricity......................................................................53 Overview...........................................................................................................53 Questions......................................................................................................... 62 Answers to questions..........................................................................................72 Topic 4 Chemical change...................................................................................79 Overview...........................................................................................................79 Questions......................................................................................................... 85 Answers to questions..........................................................................................91 Topic 5 Mechanics........................................................................................... 96 Overview.......................................................................................................... 96 Questions........................................................................................................106 Answers to questions........................................................................................ 116 Topic 6 Chemical systems...............................................................................126 Overview.........................................................................................................126 Questions........................................................................................................128 Answers to questions........................................................................................130 Exam Paper 1.................................................................................................... 132 Answers to Exam Paper 1................................................................................... 141 Exam Paper 2.................................................................................................... 147 Answers to Exam Paper 2................................................................................... 153 ©Publisher » Subject name Physical Science Grade 10 Study Guide Revision When revising, many people find it helpful to write as they work. You are more likely to remember something that you have written than something that you have just looked at in a book. You will also find that you can concentrate better and learn faster if you revise hard for a few short sessions rather than for one long one. You will find that you get more revision done in three half-hour sessions with five minute breaks in-between than in one session of 1½ hours. When you take a break, do something completely different – preferably physical. Go for a walk, jump up and down, run around the garden or kick a ball. Your memory recall of the work you have learned will be improved immensely if you go through it at regular intervals. People who have studied memory talk about the ‘forgetting curve’. Suppose you have done an hour’s revision and have learned a summary of a topic. The forgetting curve shows that whatever you are going to forget of that summary, you are likely to forget as much as half of it in the next 24 hours. If you spend just five minutes quickly going through that same summary the next day, and another five minutes a few days later, your memory recall at a later date when you write the exam will be much better. How to tackle exam questions Multiple choice questions You probably will have to answer the questions by filling in blocks on an answer sheet. Use a pencil to fill in the blocks, so that you can rub it out if you wish to change an answer. If the examination requires you to use a pen, go over them again at the end when you are satisfied with your answers. There will usually be four options to choose from in a multiple choice question. When you read the question, try to answer it in your mind without looking at the choices, then see if your answer is one of them. Sometimes the wrong choices can confuse you. There is always only one correct answer, so never fill in two blocks. If you do that, your answer will be marked wrong. You do not lose marks if you get a multiple choice question wrong, so never leave out a question simply because you are not sure of an answer. Try to eliminate some choices that you think are definitely wrong, and then guess and hope for the best. Do not go on to the next question without committing yourself to an answer to the previous question, © Via Afrika » Physical Science 3 even if you are not sure of it. Answer it, but make a mark on the question paper so that, if you have time, you can come back to it when you have finished the rest of the examination. Calculations Any answer to a question that requires a calculation must start with a statement of the principle, law or equation that is required for the calculation. If you do not state the formula first and only write down numbers and an answer, you will get no marks, even if your answer is correct. We use the SI system of units. If you are given a value in another unit, it first must be converted into the relevant SI unit before you substitute it into the equation. It is not necessary to write the unit with each substitution in the equation, provided each is in the correct SI units. You must write the correct SI unit with you final answer. So the procedure is as follows: Ensure that all given quantities are in SI units. Write the relevant equation for the calculation. If necessary, change the subject of the formula. Substitute the given values. It is not necessary to write the unit with the substitution. Carry out the calculation. Write the answer, with the correct SI unit. If the quantity is a vector quantity, write the direction. Mark allocation Marks are usually allocated as follows: One mark for the equation for the calculation. One mark for each correct substitution, in SI units. One mark for the correctly calculated answer, with the unit. If the unit is missing or incorrect, this mark is lost. One mark for the statement of the correct direction, if it is a vector quantity. Positive marking Very often questions requiring calculations are structured so that an answer to one part of the question is used in another part of the question. If you make a mistake in the first part so that the answer to that part is wrong, you will not be penalised for an incorrect answer in the later part, provided your calculations are correct. This is often called ‘positive marking’. Nevertheless, what should you do if you have no idea how to answer © Via Afrika » Physical Science 4 (say) question 2.1, but know that if only you had the answer to 2.1 you could answer 2.2? Simply assume an answer to 2.1. Write ‘2.2 Assume the answer to 2.1 is …’. Write any number with the correct unit and carry on. How to use this study guide Each topic is presented as a summary followed by a selection of examination-type questions. The summaries are the ‘bare bones’ of what you need to know for each topic. Do not try simply to learn the summaries off by heart. You must make sure that you understand each statement in the summary. If not, then refer to the Learner’s Book and study the relevant section. Once you are sure that you understand the statements, you can concentrate on learning the summary. It will be useful for you to write down the key words as they appear in the summary, then test yourself to see if you can state what is in the summary. Then work through the questions set on the topic. The answers are given at the back of the book, with an indication of how marks would be allocated in an exam. A full sample Physics examination and a full sample Chemistry examination are also provided, with answers for you to test yourself before the final exams at the end of the year. Prefixes and units You will encounter the prefixes given in the table below as you study Physical Science. You will see from the table that the prefixes that are used in science all relate to exponents that are multiples of 3. While there are prefixes for numbers bigger than 106 and also smaller than 10-15, it is sufficient for you to learn only those that are in this table. Prefix mega- kilo- unit milli- micro- nano- pico- femto- Factor × 106 × 10 3 1 × 10 –3 × 10–6 × 10–9 × 10–12 × 10–15 Symbol M K m μ n p f fW MW º kW W mW μW nW pW Example megawatt kilowatt Watt milliwatt microwatt nanowatt picowatt femto- watt Micro uses the Greek symbol μ (pronounced ‘mew’). All prefix symbols are small letters except for mega. This is to distinguish mega from milli. When writing the symbol for the prefix with the symbol for the unit (for instance, mW) there is no space or dot between the prefix and the unit. © Via Afrika » Physical Science 5 SI units used in the Grade 10 curriculum Here is a list of the symbols and SI units for quantities that you will come across in the Grade 10 curriculum. Test yourself to see that you know the symbol and unit for the quantity and the quantity for the unit. Temperature T K (kelvin) Distance D m Amplitude A m Frequency f Hz (hertz) Time t s Period T s Speed, velocity v m.s–1 Wavelength λ m Energy E J (joule) Planck’s constant h J.s Charge Q C (coulomb) Potential difference V V (volt) Emf E V (volt) Current I A (ampere) Resistance R Ω (ohm) Quantity of matter n mol Volume V m3 (or dm3 for concentration) Concentration c mol·dm–3 Pressure p Pa (pascal) Acceleration a m.s–2 © Via Afrika » Physical Science 6  Topic 1 Matter and materials Overview © Via Afrika » Physical Science 7  Topic 1 Summary 1 Revision of matter (Grade 9) 1.1 Matter and classification Matter is made up of particles (atoms or molecules) and it is the properties of the atoms or molecules that determine the characteristics and reactivity of that matter. The properties of matter include: strength; density; melting and boiling points; whether the material is brittle, malleable or ductile; whether it is magnetic or not; and its electrical and thermal conductivity. Elements and compounds are classified as pure because they contain particles that are all the same. Substances can be classified as pure – elements and compounds – or mixtures. Pure substances contain particles that are all the same. Elements and compounds can be represented by symbols and formulae. Some of the names, symbols or formulae of a number of common elements and compounds that you should have learnt are the following: Elements: S for sulphur; C for carbon; P for phosphorus (note the spelling); H for hydrogen; O for oxygen; He for helium; N for nitrogen; F for fluorine; Mg for magnesium; Ca for calcium; Zn for zinc. Compounds: H O for water; H SO for sulphuric acid; HCl for hydrochloric acid; 2 2 4 NaCl for sodium chloride (table salt); CaCO3for calcium carbonate; KNO3 for potassium nitrate; Na3PO4 for sodium phosphate. You will notice that the naming of compounds follows these rules: The metal or hydrogen is always named first, then the non-metal (potassium iodide: KI; hydrogen chloride: HCl (also called hydrochloric acid)). The name of a non-metal ion of an element always ends in –ide (for instance, sodium chloride: NaCl). The name of a non-metal complex ion (more than one element in the ion) usually ends in –ate or –ite (for instance, copper sulphate: CuSO4; potassium sulphite: K2SO3). An exception to this is hydroxide (for instance, sodium hydroxide: NaOH). Mixtures consist of different substances, and can be homogeneous (have the same ‘look’ throughout) or heterogeneous (you can see the different substances). They can be separated in various ways, for instance filtering, sieving, chromatography, distilling or dissolving one constituent. Some of the properties of metals are that they conduct electricity and heat, and they are malleable and ductile. Non-metals are non-conductors of electricity and heat. They are gases, liquids or brittle solids, and bond with each other. Metalloids are elements on the border between metals and non-metals, and they have both metal and non-metal properties. © Via Afrika » Physical Science 8  Topic 1 2 States of matter and the kinetic molecular theory The kinetic molecular theory, together with an understanding of intermolecular forces, explains how matter can exist as solids, liquids or gases. The kinetic molecular theory can also be used to explain diffusion and Brownian motion. The kinetic molecular theory says that: Matter is made up of particles that are constantly moving. Particles have energy that varies according to whether they are in the gas (most energy), liquid or solid (least energy) phase. The temperature of a substance is a measure of the average kinetic energy of its particles. A change in phase may occur when the energy of the particles is changed by heating or cooling. There are spaces between the particles. These are greatest in the gas phase and least in the solid phase. Melting (solid → liquid or liquid → solid) points and boiling (liquid → gas or gas → liquid) points are the temperatures at which phase changes happen. They are also specific to pure substances. Sublimation is the change from solid to gas without going through the liquid phase, for instance, solid CO2 (dry ice) sublimates to CO2 (gas). Brownian motion is the random movement of gas and liquid particles. (‘Random’ means that any one particle can be moving in any possible direction at that instant.) Diffusion occurs mostly in gases and liquids. It is the movement of particles of one kind from an area where there are many to an area where there are few. This can happen because of the random movement of all particles and because there are large spaces between particles in the gas and liquid phases. 3 The atom – the basic building block of matter 3.1 The models of the atom Matter is any substance that has a mass and occupies a volume. A number of models have been developed by different scientists explaining the structure of these atoms. Some of these models are described below: Democritus – developed the particle theory of matter. He stated that if you kept dividing something, eventually you would get to a point where it can no longer be divided. He called this indivisible substance ‘atomos’. Dalton – said all matter consists of atoms that cannot be made or destroyed. Atoms of the same element are all the same and atoms can be joined together. Thomson – developed the ‘currant bun’ model. An atom consists of a solid, positively charged mass in which tiny negatively charged particles are scattered. Rutherford – said an atom contains a central, positively charged mass known as the nucleus. © Via Afrika » Physical Science 9  Topic 1 Bohr – said negatively charged electrons are contained within certain areas in the atom known as ‘energy shells’. Schrödinger – developed the ‘wave model’ of the atom in which atoms behave as waves rather than as particles. 3.2 The structure of the atom The atom consists of a central nucleus containing positively charged protons and neutral neutrons. Together these are known as nucleons. Surrounding the nucleus is a number of energy shells containing negatively charged electrons. The number of protons in the nucleus is called the atomic number (Z). In a neutral atom, the number of protons is equal to the number of electrons. The number of protons and neutrons (added together) in the nucleus is called the mass number (A). A = Z + N Mass Atomic Number of number number neutrons An atom can either gain or lose electrons in order to form a charged particle, known as an ion. A positive ion is formed when an atom loses electrons, while a negative ion is formed when an atom gains electrons. The mass of an atom (atomic mass) is determined by the number of protons and neutrons. Mass of a proton = mass of a neutron = 1 mass unit. 3.3 Isotopes Isotopes are atoms of the same element that contain the same number of protons, but different numbers of neutrons. They have the same atomic number, but different mass numbers. In the periodic table, two numbers are given with the symbol of each element. These numbers are the atomic number and the average atomic mass. In any element, the ratio of the isotopes is constant. The atomic mass is given as the average mass of all the atoms in the sample of the element. We can use the percentage composition of the isotopes of an atom to determine the average mass of the element. Example: 75% of all naturally occurring chlorine atoms have an atomic mass of 35, while 25% have an atomic mass of 37. We can use these values to calculate the average atomic mass that will appear on the periodic table. We do this by multiplying the percentages of each isotope by their respective atomic masses © Via Afrika » Physical Science 10  Topic 1 and then dividing the answer by 100. Atomic mass of chlorine = [(75 × 35) + (25 × 37)] / 100 = 35,5. 3.4 Electron configuration Electron configuration refers to the arrangement of electrons in an atom. Electrons occupy orbitals arranged within energy shells (numbered 1, 2, 3 …) around the nucleus. These correspond to the periods in the periodic table. Orbitals are regions where electrons spend most of their time. Each orbital can contain a maximum of two electrons. The s-orbital is spherical (ball-shaped). Each energy shell has only one s-orbital. p-orbitals are shaped like dumb-bells. There are no p-orbitals in the first shell. The other shells each contain three p-orbitals, named px, py and pz. Each orbital can hold two electrons, which means that the three p-orbitals in a shell can hold six electrons in total. Scientists use Aufbau diagrams (arrows in boxes) to represent the electron configuration of an atom. The shell closest to the nucleus is number 1, the next number is 2, and so on. © Via Afrika » Physical Science 11  Topic 1 Energy level Types of orbitals Maximum number of electrons contained 1 Only an s-orbital 2 electrons in the s-orbital 2 An s- and 3 p-orbitals 2 electrons in the s-orbital and 6 electrons in the p-orbitals 3 An s- and 3 p-orbitals 2 electrons in the s-orbital and 6 electrons in the p-orbitals Example: An Aufbau diagram for fluorine Fluorine contains nine electrons. This means its electron configuration is 1s22s22p5. Each orbital must contain the maximum number of electrons before you can move on to the next orbital. As you can see, each electron is represented by an arrow. Rules for drawing Aufbau diagrams: You must always fill up the lower orbitals before you can move on to the next energy level. Pauli’s exclusion principle: ‘Each orbital may contain a maximum of 2 electrons, spinning oppositely’. This is why in each orbital the one arrow faces up, while the other faces down. Hund’s rule: ‘Electrons occupy equivalent orbitals (like the p-orbitals in a shell) singly, before pairing takes place’. © Via Afrika » Physical Science 12  Topic 1 4 The periodic table © Via Afrika » Physical Science 13  Topic 1 The elements are arranged in order of increasing atomic number. The zig-zag (step) line separates the metals (on the left) from the non-metals (on the right). The numbered columns are called groups and are numbered from I to VIII. If the transition metals are included, then the numbers run from 1 to 18. The numbered rows are called periods. This number tells you how many energy levels or electron shells there are. In some groups the properties of the elements in the group are similar (for instance, the alkali metals of group I, the non-metal halogens of group VII) The properties change gradually as you move across a period (for instance, change from metal to non-metal). Characteristics that change across the periodic table include the following: Atomic radius: This is the distance from the centre of the nucleus to the outer energy shell, and it increases down a group and across a period. Ionisation energy: This is the energy needed to remove an electron from an atom of that element in the gas phase, and it increases across a period but decreases down a group. Electron affinity: This is the energy change when an electron is added to an atom of an element in the gas phase, and it increases across a period and down a group. Electronegativity: This is the ability of an atom to attract the electrons making a bond it is involved in, and it increases across a period but decreases down a group. 5 Chemical bonding The electrons found in the outermost energy shells are known as valence electrons and they control how an atom reacts. The number of valence electrons equals the group number. All atoms try to get a full outer shell of electrons. They can achieve this by gaining electrons from another atom, losing electrons to another atom or sharing electrons with another atom. Covalent and ionic bonding are shown using Lewis diagrams. 5.1 Lewis diagrams (dot-cross diagrams) Dots or crosses are used to represent the valence electrons of an atom. Rules for drawing Lewis diagrams: Write the symbol for the element and then draw a cross or dot on top of the symbol. Work in a clockwise direction. The electrons are only paired once the first four dots or crosses have been drawn. © Via Afrika » Physical Science 14  Topic 1 5.2 Formation of ions An ion is a charged particle that forms when a neutral atom either gains or loses electrons. Atoms lose or gain electrons in order to obtain a full outer energy shell. Group Charge on the ion I +1 II +2 III +3 IV These elements do not form ions. V –3 VI –2 VII –1 Elements in group VIII will not form ions, as they already have a full outer shell of electrons. 5.3 Ionic bonding Ionic bonding occurs between metals, which form positive ions, and non-metals, which form negative ions. Ionic bonding follows these rules: The metal will form a positive ion with a charge equal to the number of electrons it has lost. The non-metal ion is written in square brackets. Its charge is equal to the number of electrons gained. The square brackets must contain the transferred electrons as well as those of the non-metal ion. 5.4 Covalent bonding A covalent bond is formed by overlapping orbitals that share of a pair of electrons. In this way, both atoms obtain a full outer energy shell. Water is an example of a covalent compound. Each oxygen atom requires two electrons in order to obtain a full energy shell. This means that two hydrogen atoms are needed. In this case, two single bonds are formed. © Via Afrika » Physical Science 15  Topic 1 An oxygen molecule contains a double bond, as each oxygen atom shares two electrons. It can be written as O=O. 5.5 Metallic bonding The valence electrons of metals are loosely held by the nucleus. They move out of position, and become ‘delocalised’ or free electrons. The structure is held in place by the strong electrostatic force between the positively charged metal ions and the negatively charged delocalised electrons. 5 Particles that make up substances 6.1 Covalent molecular substances Molecules are formed when non-metal atoms are covalently bonded together. We can represent molecules by using different circles. Each atom is represented by a circle of a different colour and size. 6.2 Ionic substances Ionic substances, also known as salts, are formed when a metal atom transfers electrons to a non-metal atom. The electrostatic attraction between the positive and negative ions is what holds the crystal lattice together. 6.3 Covalent network structures Covalent network structures are giant molecular compounds formed by a large number of atoms that are covalently bonded together to form a highly regular lattice. Diamond and graphite are examples of such covalent network structures. © Via Afrika » Physical Science 16  Topic 1 In diamonds, each carbon atom is attached to four other carbon atoms. Graphite consists of layers of carbon atoms. Each carbon atom is attached to three other atoms within the layer. The layers are weakly bonded together and can slide apart easily, which means that graphite is soft. Graphite is used in pencils and as a lubricant in machinery. 6.4 Metallic substances A metal substance is one that forms when a group of atoms has a pool of delocalised electrons that surround a lattice of regularly spaced positive ions. Most metals are shiny and hard. 6.5 Summary Ionic Covalent Metallic Bonding: (between metals (between non- (between metals) and non-metals) metals) Structure: Giant ionic Covalent network Molecular Giant metallic Sodium chloride Diamond Iodine Zinc Example: © Via Afrika » Physical Science 17  Topic 1 Questions Question 1: Multiple choice Choose the correct answer. Only write the letter of the answer you select. 1.1 Where are metals found on the periodic table? A At the bottom B To the right C To the left D At the top (3) 1.2 What is the name given to the group VII elements? A Alkali metals B Alkaline earth metals C Halogens D Nobel gases (3) 1.3 What change to a neutral atom will result in the formation of a negative ion? A It gains an electron. B It gains a proton. C It loses an electron. D It loses a proton. (3) 1.4 Which statement about the numbers of particles in atoms is correct? Apart from hydrogen, most atoms contain: A more neutrons than protons. B more protons than neutrons. C more electrons than protons. D more protons than electrons. (3) 1.5 Metal atoms form: A positive anions. B negative anions. C negative cations. D positive cations. (3) 1.6 Which are the correct formulae for sodium chloride and calcium carbonate? A NaCl and CaCO3 B SCl and CaCO3 C NaCl and CaCO2 D NaCl and CmCO3 (3) 1.7 Which of the elements below has an electron configuration of 1s22s22p4? A sodium B chlorine C oxygen D fluorine (3) © Via Afrika » Physical Science 18  Topic 1 1.8 Which of the following terms describes the change in state that occurs when a liquid changes into a solid? A condensation B evaporation C freezing D sublimation (3) 1.9 Copper has two isotopes; 69,1% of copper isotopes have a mass of 63 and 30,9% have a mass of 65. What is the average mass of a copper atom? A 65 B 66 C 64,4 D 63,6 (3) 1.10 In which of the following compounds are electrons shared between atoms? 1 sodium fluoride 2 nitrogen dioxide 3 iron bromide A 1 only B 2 only C 1 and 3 D 1, 2 and 3 (3) 1.11 Which compound contains two double bonds in which electrons have been shared? A hydrogen bromide B carbon dioxide C sodium iodide D water (3) 1.12 In the molecules CH4, HBr and H2O, which atoms use all of their outer shell electrons in bonding? A C and Br B C and H C Br and H D H and O (3) 1.13 The following statement is about chemical bonding. Covalent bonds are formed by the … of electrons. Covalent bonds occur between... Which combination of words completes the statement? (3) A transfer two non-metals B transfer a non-metal and a metal C sharing two metals D sharing two non-metals © Via Afrika » Physical Science 19  Topic 1 1.14 Which of the elements below is most likely to form a positive ion? A zinc B chlorine C oxygen D fluorine (3) 1.15 Which substance when combined with oxygen will form a covalent bond? A sodium B magnesium C boron D aluminium (3) Question 2: Matching pairs Choose an item from column B that matches the description in column A. Write only the letter of your choice (A–J) next to the question number. Column A Column B 2.1 formation of A – the number of protons and neutrons added together positive ions 2.2 mass number B – loss of electrons 2.3 group VIII C – when a substance changes from a liquid to a solid state elements 2.4 chromatography D – the number of protons and electrons added together 2.5 condensation E – halogens F – gain of electrons G – separation of mixtures of pigments/colours H – when a substance changes from a gas to a liquid state I – separation of a solid from a liquid J – noble gases Question 3: True/false Indicate whether the following statements are true or false. If the statement is false, write down the correct statement. 3.1 Isotopes are elements with the same number of protons, but different numbers of electrons. (2) 3.2 Isotopes contain the same number of electrons in their outermost energy shell. (2) 3.3 Sodium has an electron configuration of 1s 2s 2p 3s. 2 2 6 1 (2) 3.4 Calcium and magnesium both form anions with a charge of +2. (2) 3.5 A mixture can be separated into its component substances by physical means. (2) © Via Afrika » Physical Science 20  Topic 1 Question 4: One-word answers Provide one word or term for each of the descriptions. Write only the word or term next to the question number. 4.1 The movement of particles from a region where there are many to a region where there are fewer. (1) 4.2 The basic building block of matter. (1) 4.3 The electrons found in the outermost energy shell. (1) 4.4 A mixture in which the different substances that make up that mixture can be seen. (1) 4.5 The type of chemical bonding that occurs when electrons are transferred from one atom to another. (1) Question 5: Long questions Mixtures can be homogeneous or heterogeneous. 5.1 What is the difference between a homogeneous mixture and a heterogeneous mixture? (2) 5.2 Give one example of each. (2) 5.3 How do mixtures differ from compounds? (2) 5.4 Which of the following substance is pure? sugar sea water steel (1) Question 6: Long questions The following are the melting points of the metals in group II on the periodic table: beryllium 1278 °C magnesium 649 °C calcium 839 °C strontium 769 °C barium 725 °C 6.1 What is the general trend in melting points as you go down the group? (1) 6.2 One metal does not fit this trend. Which one is it? (1) 6.3 Does this information support the idea that beryllium atoms are held together more strongly than barium atoms? (1) 6.4 Explain your answer to question 6.3. (2) © Via Afrika » Physical Science 21  Topic 1 Question 7: Long questions Use the table below to answer the questions that follow. Substance Melting point (°C) Boiling point (°C) lead 317 174 radon –71 –62 ethanol –117 78 cobalt 1492 2900 nitrogen –210 –196 propane –188 –42 ethanoic acid 16 118 7.1 Define the boiling point of a substance. (2) 7.2 Which two substances are gaseous at –50 °C? (2) 7.3 Which substance is a liquid at 2500 °C? (1) 7.4 Is nitrogen a liquid, solid or gas at 35 °C? (1) Question 8: Long questions The table below shows information about two isotopes of chlorine. Atom Number of protons Number of Number of neutrons electrons Chlorine-35 A 17 18 Chlorine-37 17 B C 8.1 Replace the letters with the correct numbers to complete the table. (3) 8.2 Define isotopes. (2) 8.3 Draw an Aufbau diagram of a chlorine atom. (2) 8.4 A chlorine ion has a charge of –1. Write down the electron configuration for a chlorine ion. (1) Question 9: Long questions The diagram below shows the electron configuration of four different elements. element 1 element 2 element 3 element 4 © Via Afrika » Physical Science 22  Topic 1 9.1 Which element has an atomic number of 3? (1) 9.2 Which atom has the electron configuration 1s22s2 2p63s2? (1) 9.3 Which element is nitrogen? (1) Question 10: Long questions The structure of a typical ionic compound is a regular arrangement of positive and negative ions. 10.1 What is the name of this regular arrangement of particles? (1) 10.2 Name an ionic substance. (1) 10.3 Ions are formed by electron loss or gain. 10.3.1 Give the formula of the magnesium ion. (1) 10.3.2 Give the formula of the oxide (oxygen) ion. (1) 10.3.3 Why are these two ions attracted to each other? (1) 10.3.4 Draw a Lewis diagram to show the bonding that takes place between a magnesium and oxygen atom. (3) Question 11: Long questions The table below describes the number of protons, neutrons and electrons found in three different substances: A, B and C. Particle Number of protons Number of electrons Number of neutrons A 15 15 16 B 15 18 16 C 15 15 17 Use the information in the table to explain why the following statements are true. 11.1 Particle A is a neutral atom. (1) 11.2 They are all particles of the same element. (1) 11.3 Particle B is a negative ion. (1) 11.4 Particles A and C are isotopes. (2) © Via Afrika » Physical Science 23  Topic 1 11.5 What is the charge on particle B? (1) 11.6 Is particle B a metal or a non-metal? Give a reason for your answer. (2) © Via Afrika » Physical Science 24  Topic 1 Answers to questions Answers to questions Question 1: Multiple choice 1.1 C üüü 1.2 C üüü 1.3 A üüü 1.4 B üüü 1.5 D üüü 1.6 A üüü 1.7 C üüü 1.8 C üüü 1.9 D üüü 1.10 B üüü 1.11 B üüü 1.12 B üüü 1.13 D üüü 1.14 A üüü 1.15 C üüü Question 2: Matching pairs 2.1 Bü 2.2 Aü 2.3 Jü 2.4 Gü 2.5 Hü Question 3: True/false 3.1 False ü – Isotopes have the same number of protons, but different numbers of neutrons. ü 3.2 True üü 3.3 True üü 3.4 False ü – Sodium and calcium both form cations with a charge of +2. ü 3.5 True üü © Via Afrika » Physical Science 25  Topic 1 Answers to questions Question 4: One-word answers 4.1 diffusion ü 4.2 atom ü 4.3 valence electrons ü 4.4 heterogeneous ü 4.5 ionic ü Question 5: Long questions 5.1 In a homogeneous mixture, the substances that make up the mixture are not visible as separate substances ü whereas in a heterogeneous mixture they are. ü 5.2 Homogeneous – sea water, fruit juice, tea, coffee, steel (any correct one) ü Heterogeneous – granite, nuts and raisins, smoke, oil and water, box of biscuits (any correct one) ü 5.3 In mixtures, the substances that make up that mixture can be in variable proportions. ü In compounds, the elements combine in fixed ratios. ü Mixtures can be separated by physical means, while compounds can only be separated by chemical means. ü 5.4 Only sugar is a compound. The rest are mixtures. ü Question 6: Long questions 6.1 melting points decrease ü 6.2 magnesium ü 6.3 yes ü 6.4 because the melting point of beryllium is much higher,ü so more energy is needed to melt it ü Question 7: Long questions 7.1 The boiling point of a substance is the temperature ü at which that substance changes from a liquid into a gas. ü 7.2 radon ü and nitrogen ü 7.3 cobalt ü 7.4 gas ü © Via Afrika » Physical Science 26  Topic 1 Answers to questions Question 8: Long questions 8.1 A 17 ü B 17 ü C 20 ü 8.2 Elements with the same atomic number, ü but different mass numbers. ü 8.3 correct number of electrons ü correct placement of electrons ü 8.4 1s22s22p63s23p6 ü Question 9: Long questions 9.1 element 1 ü 9.2 element 3 ü 9.3 element 2 ü Question 10: Long questions 10.1 crystal lattice ü 10.2 Any metal atom combined with a non-metal atom. ü 10.3 10.3.1 Mg+2 ü 10.3.2 O–2 ü 10.3.3 The electrostatic attraction between oppositely charged ions. ü © Via Afrika » Physical Science 27  Topic 1 Answers to questions 10.3.4 correct number of valence electrons ü correct placement of valence electrons ü correct charges of ions ü Question 11: Long questions 11.1 It has the same number of protons as electrons. ü 11.2 They all have the same number of protons. ü 11.3 It has more electrons than protons. ü 11.4 They have the same number of protons, ü but different numbers of neutrons. ü 11.5 –3 ü 11.6 It is a non-metal,ü as it has formed a negative ion. ü © Via Afrika » Physical Science 28  Topic 2 Waves, sound and light Overview © Via Afrika » Physical Science 29  Topic 2 Summary 1 Transverse pulses and waves 1.1 Properties of transverse pulses and waves A pulse is a single disturbance in a medium. A single crest is a transverse pulse. A single trough is also a transverse pulse. In a transverse pulse or wave, the particles of the medium vibrate at 90° to the direction in which the pulse or wave moves. The amplitude of a pulse is the maximum displacement from the position of rest of a particle in the medium. A wave is made up of one pulse after another. The ‘hump’ in a transverse wave is called a crest. The ‘hollow’ in a transverse wave is called a trough. Continuous transverse waves are produced by continuous vibrations of the medium. A vibration is a regular to-and-fro movement (up-and-down or forwards-and- backwards). The rest position of a vibrating object (also called the equilibrium position) is the position that it would be in when not vibrating. One complete vibration (also called one oscillation) is one complete to-and-fro movement. It is the movement from the rest position to the furthest point in one direction, then to the furthest point in the opposite direction, then back to the rest position. One complete vibration (or one oscillation) of the end of a slinky spring will produce one wavelength in the spring. Particles in a medium are in phase if they are vibrating perfectly in step with one another. Particles in a medium that are not vibrating perfectly in step with one another are out of phase. Two particles are completely out of phase if they are moving oppositely, with one reaching the crest at the same instant that the other reaches the trough. 1.2 Wavelength, frequency, amplitude, period, wave speed Wavelength () is the distance between two consecutive points that are in phase. For transverse waves, wavelength is the distance between two successive crests or two successive troughs. The unit is metres (m). If the wavelength is given in any other unit (for instance, mm or nm), it must be converted to metres when doing a calculation. Frequency (f) is the number of wavelengths passing per second. It equals the frequency of the vibration making the waves. The unit is s–1 (per second). 1 s–1 is called a hertz (Hz). The amplitude of a wave is the maximum distance that a point in a wave moves from its rest position. This equals the distance from the rest position to the top of a crest or to the bottom of a trough. The unit is metres (m). © Via Afrika » Physical Science 30  Topic 2 The speed of a wave (v) is the distance moved by any pulse in the wave per second. The speed can change as the medium changes. The unit is metres per second (m.s–1). If the speed is given in any other unit (for instance, km hr–1), it must first be converted to m.s–1 before doing a calculation. Distance moved (in m) Speed is calculated using the formula: speed (in m.s–1) = time taken (in s) The wave equation relates the above three quantities: v = f  The period (T) of a wave is the time taken for one wavelength to pass. The unit is seconds (s). T = 1 / f Period and frequency are inversely proportional to each other. If the frequency is doubled, the period is halved. It also equals the period of the vibration making the wave. If T = 1 / f , it follows that f = 1 / T. If we take the wave equation v = f  and substitute 1 / T for f, we have v =  / T. 1.2.1 Worked example A transverse wave is set up in a slinky spring lying on a long table. The wavelength is 540 mm. One wavelength passes a mark on the table every 0,8 s. Calculate: 1 the frequency of the wave 2 the speed of the wave. Answers: 1 T = 0,6 s f=? 1 1 f = = T 0,8 © Via Afrika » Physical Science 31  Topic 2 = 1,25 Hz 2 f = 1,25 Hz  = 540 mm = 0,54 m v=? v = f = 1,25 × 0,54 = 0,675 m.s–1 1.3 Superposition of pulses Superposition is the addition of the amplitudes of two pulses that occupy the same space at the same time. If a crest is considered positive, then a trough is negative. When waves meet, they interfere. Crest meeting crest or trough meeting trough results in a bigger amplitude – constructive interference. Crest meeting trough results in a smaller amplitude – destructive interference. Two pulses will cancel out to produce zero amplitude only if: one is a crest, the other a trough their amplitudes are equal their pulse lengths are equal. 2 Longitudinal waves and sound 2.1 Longitudinal pulses and waves A pulse is a single disturbance in a medium. A single compression (particles close together) or a single rarefaction (particles far apart) are each longitudinal pulses. The amplitude of a pulse is the maximum displacement from the position of rest of a particle in the medium. So it is the distance from the rest position to the centre of a compression, or the distance from the rest position to the centre of a rarefaction. In a longitudinal wave, the particles of the medium vibrate in line with the direction in which the wave moves. Longitudinal waves are made up of alternate compressions (particles close together) and rarefactions (particles far apart). Wavelength () is the distance between two consecutive points that are in phase. For longitudinal waves, wavelength is the distance between two successive compressions or two successive rarefactions. The unit is metres (m). If the wavelength is given in any other unit (for instance, mm or nm), it must be converted to metres when doing a calculation. Frequency (f) is the number of wavelengths passing per second. It equals the frequency of the vibration making the waves. The unit is s–1 (per second). 1 s–1 is called a hertz (Hz). The amplitude of a wave is the maximum distance that a point in a wave moves from its rest position. For a longitudinal wave, it is the distance from the rest position to the centre of a compression or to the centre of a rarefaction. The unit is metres (m). © Via Afrika » Physical Science 32  Topic 2 The period and frequency of a longitudinal wave have the same meaning as for a transverse wave. Period is the time taken for one wavelength to pass, for instance, the time between two successive compressions, measured in seconds. Frequency is the number of wavelengths that pass per second, measured in Hz. The equations T = 1 / f and v = f  are applied as for transverse waves. 2.2 Sound waves Only vibrating objects produce sound. Energy is therefore needed to produce sound. A material medium is required for sound to move. Sound cannot pass through a vacuum. Sound energy moves through a medium as longitudinal waves. Alternate compressions and rarefactions pass through the medium. The speed, frequency and wavelength of sound are related by the equation: Speed = frequency × wavelength v=f The speed of sound in air is approximately 340 m.s–1. The speed is dependent on the medium and its temperature. Solids transmit sounds best, gases worst. The same sound is heard loudest through solids, next loudest through liquids and softest through gases. Sound moves fastest through solids and slowest through gases. In gases, the greater the mass of the gas molecules, the slower the sound. In air, the higher the temperature the faster the sound. 2.3 Pitch and loudness The frequency of a sound wave is determined by the frequency of the vibration that causes it. If the sound wave passes into another medium, say from air into water, the speed of the wave changes, but the frequency stays the same. The pitch of a note is its position on a musical scale. As the frequency of a sound wave increases, so the pitch rises. Loudness is determined by the amplitude of the sound wave. The greater the amplitude, the louder the sound. Ultrasound has frequencies between 20 kHz and 100 kHz, higher than the range of human hearing. Ultrasound is used to produce internal images of the body (for instance, of a baby in the womb). The sound is reflected differently by the different layers in the body. 3 Electromagnetic radiation 3.1 Wave nature and spectrum The spectrum of visible light is only a small part of a broad range of waves that travel through a vacuum at the speed of light. The full range is called the electromagnetic spectrum. © Via Afrika » Physical Science 33  Topic 2 Electromagnetic waves are produced by accelerating charges. For example, in a radio aerial, changing electric fields accelerate electrons back and forth. This produces a changing magnetic field at right angles to the aerial. This in turn produces changing electric fields at right angles, and the process continues with each field generating the other. The crests and troughs in the wave indicate points where the electric or magnetic fields are strongest. Electromagnetic waves are transverse and consist of changing electric fields and magnetic fields at 90° to each other. Electromagnetic waves travel through space at 3 × 108 m.s–1. The wave equation c = f  applies. Different sections of the spectrum have different names. In order of increasing wavelength (or decreasing frequency), these are: gamma rays, X-rays, ultraviolet light, visible light, infrared, microwave, TV and radio. Gamma rays are produced by radioactive material. They have the highest frequency and the highest energy and are the most penetrative and the most dangerous. They can destroy human cells and cause cancer. Radio waves at the opposite end of the spectrum are far less penetrative and not dangerous. X–rays are produced when high-speed electrons strike a metal plate. They can be used to produce a photographic image of the human body. They cannot pass through lead. Ultraviolet radiation is produced by very hot objects. Ultraviolet rays are very harmful to the eyes, cause tanning and can cause skin cancer. Some chemicals fluoresce in UV light. Infrared radiation is heat radiation, produced by vibrating atoms and molecules in hot objects. TV remotes work by sending out infra-red pulses. 3.2 The wave and particle nature Electromagnetic waves are radiated in packages, called quanta. A quantum of light is called a photon. © Via Afrika » Physical Science 34  Topic 2 Electromagnetic radiation has both a wave nature (transverse electric and magnetic fields) and a particle nature (quanta of energy). Radio waves have such long wavelengths that their particle nature is negligible. Gamma rays have such short wavelengths that their wave nature is negligible. Visible light (in the middle of the electromagnetic spectrum) behaves both as waves and as particles. This is known as the dual nature of light. The energy of a quantum can be calculated using the equation: E=hf=hc/ where h = 6,63 × 10–34 J.s (Planck’s constant) and c = 3 × 108 m.s–1 3.2.1 Worked examples 1 The energy of a photon of light is 5,3 × 10–19 J. Calculate the frequency of the light waves. 2 Calculate the energy of a microwave quantum of wavelength 0,2 m. Answers: 1 E = 5,3 × 10-19 E = h f f = E / h = 5,3 × 10-19 / 6,63 × 10–34 f = 7,99 × 1014 Hz (6,63 × 10–34) × (3 × 108) 2 E = hc /  = 0,2 E = 9,95 × 10 –25 J Questions Question 1: Multiple choice Choose the correct answer. Write down only the letter of the answer you select. 1.1 What is the angle between the electric and magnetic fields in an electromagnetic wave? A 0° B 90° C 180° D 360° (3) © Via Afrika » Physical Science 35  Topic 2 1.2 What is the period of a wave with a frequency of 5 Hz? A 0,2 s B 5,0 s C 2,0 s D 20,0 s (3) 1.3 Two transverse pulses meet and cancel out through a process called: A diffraction. B reflection. C constructive interference. D destructive interference. (3) 1.4 In order to calculate the speed of a wave, which formula would you use? A wavelength ÷ frequency B frequency ÷ wavelength C wavelength ÷ period D frequency × period (3) 1.5 The speed of a water wave is 4 m.s. If the frequency is 8 Hz, what is the -1 wavelength? A 32 m B 2m C 12 m D 0,5 m (3) 1.6 A vibrating hacksaw blade completes 40 oscillations (complete vibrations) in 5 s. What is its period? A 8s B 0,125 s C 0,2 s D 0,025 s (3) 1.7 The speed at which water molecules are moving in a wave in a ripple tank: A is greatest in a trough. B is greatest in a crest. C is smallest in the rest position. D is greatest in the rest position. (3) 1.8 Sound travels fastest through a: A solid. B liquid. C gas. D vacuum. (3) 1.9 The sketch shows a rope with two pulses of equal amplitude approaching each other. When the two pulses pass through point X, what is the maximum ampli- tude of the pulse? © Via Afrika » Physical Science 36  Topic 2 A D B 0 C 2D D ½D (3) 1.10 Which diagram below has both the wavelength () and the amplitude (A) la- belled correctly? A B © Via Afrika » Physical Science 37  Topic 2 C D (3) 1.11 Sound is: 1 a series of moving compressions and rarefactions. 2 an example of a transverse wave. 3 able to travel through a vacuum. 4 an example of a longitudinal wave. Which of the above statements about sound is/are correct? A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 1 and 4 (3) 1.12 The wavelength of a particular form of electromagnetic radiation in a vacuum is 10–12 m. The wavelength of a form of electromagnetic radiation of twice the frequency is: A 2,5 × 10–13 m. B 10–6 m. C 5 × 10–13 m. D 2 × 10–12 m. (3) © Via Afrika » Physical Science 38  Topic 2 1.13 The energy of a photon of electromagnetic energy can be calculated using the equation: A E = hf. B E = h ÷ f. C E =  ÷ hc. D E = h ÷ c. (3) Question 2: True/false Indicate whether the following statements are true or false. If the statement is false, write down the correct statement. 2.1 In a longitudinal wave, each particle in the medium is travelling fastest as it passes through the rest position. (2) 2.2 In a transverse wave, a pulse length is equal to a wavelength. (2) 2.3 Wavelength is the maximum displacement from the position of rest. (2) 2.4 An increase in frequency of a sound wave and a simultaneous increase in amplitude will cause a note that is louder and has a lower pitch. (2) 2.5 The energy of electromagnetic radiation is directly proportional to the wavelength of the radiation. (2) Question 3: One-word answers Provide one word or term for each of the following descriptions. Write only the word or term next to the question number. 3.1 The colour of visible light that has the shortest wavelength, highest frequency and greatest energy. (1) 3.2 A region in a longitudinal wave where the particles of the medium have been pulled far apart. (1) 3.3 The type of electromagnetic radiation that is responsible for us feeling the heat from the sun. (1) 3.4 The distance between two consecutive points in a longitudinal wave that are in phase. (1) 3.5 A quantum of visible light. (1) Question 4: Matching pairs Choose an item from column B that matches the description in column A. Write only the letter of your choice (A–J) next to the question number. © Via Afrika » Physical Science 39  Topic 2 Column A Column B 4.1 released during nuclear reactions AS 4.2 a unit for frequency B electric field 4.3 a charged particle experiences a force C gamma rays 4.4 distance moved per second D speed 4.5 a quantum of visible light E s–1 F photon G magnetic field H microwaves I proton J frequency Question 5: Long questions The sketch below shows a pendulum consisting of a weight attached to the end of a length of string. The pendulum was set in motion by pulling the weight to position A and releasing it. Explain the meaning of each of the following terms, making use of the positions shown in the sketch where appropriate. 5.1 one oscillation (or complete vibration) (2) 5.2 the rest position (or equilibrium position) (2) 5.3 frequency (2) 5.4 amplitude (2) 5.5 period (2) 5 × 2 = Question 6: Long questions The sketch below shows a transverse wave in a medium. © Via Afrika » Physical Science 40  Topic 2 Use the letters supplied in the sketch to indicate the following: 6.1 the rest position (position of equilibrium) (2) 6.2 two points that are in phase (2) 6.3 a crest 2) 6.4 amplitude (2) 6.5 two points completely out of phase (2) 6.6 wavelength (2) 6 × 2 = Question 7: Long questions Refer again to the illustration in question 6. Ten wavelengths pass point B in 2 seconds. The distance between points B and F is 300 mm. Calculate (in SI units): 7.1 the frequency (2) 7.2 the period (3) 7.3 the speed of the waves. (4) Question 8: Long questions © Via Afrika » Physical Science 41  Topic 2 Each particle in the wave shown above completes one vibration (oscillation) in 0,4 s. 8.1 How long will it take eight wavelengths to pass a specific point in the medium? (2) 8.2 What is the amplitude of this wave? (2) 8.3 What is the period of this wave? (2) 8.4 What is the wavelength of this wave? (2) 8.5 Calculate the frequency of the wave. (3) 8.6 Calculate the speed of the wave. (4) Question 9: Long questions Two beads are attached to the vibrator of a ripple tank and are positioned so that they dip into the water, as shown in the photo above. The resultant pattern is shown in the second photograph. 9.1 What is the phenomenon in the tank called? (2) 9.2 What do the fan-shaped lines in the second photo represent? (2) 9.3 How are these lines formed? (2) Question 10: Long questions 10.1 What type of wave is a sound wave that reaches your ear? (2) 10.2 Explain briefly how you would use a slinky spring to demonstrate this type of wave to a friend. (4) 10.3 What is meant by the ‘wavelength’ of this type of wave? (2) © Via Afrika » Physical Science 42  Topic 2 Question 11: Long questions A typical sound wave associated with human speech has a frequency of 500 Hz, while the frequency of yellow light is about 5 × 1014 Hz. Assuming that sound travels at 340 m.s-1 and light at 3 × 108 m.s–1: 11.1 Calculate the wavelength of the sound wave. (4) 11.2 Calculate the wavelength of yellow light. (3) 11.3 Express the wavelength of yellow light in nanometres. (1) Question 12: Long questions 2.1 Describe an experiment or demonstration that shows that sound cannot travel in a vacuum. (5) 12.2 Why is the moon sometimes referred to as ‘the silent planet’? (2) 12.3 The speed of sound in air is 340 m.s. Calculate the wavelength of the sound –1 produced by a tuning fork of frequency 156 Hz. (4) 12.4 Calculate the period of this sound wave. (3) 12.5 What is the sound called that has a frequency higher than the human ear can hear? (1) 12.6 Describe one use for this type of high-frequency sound wave. (2) Question 13: Long questions Vibrations of frequency 2,0 Hz are produced by a generator attached to a spring. These vibrations are at 90° to the spring. The waves that it produces have a wavelength of 0,45 m. 13.1 What type of wave is passing along the spring? (1) 13.2 How many complete wavelengths pass a point in the spring in 3 seconds? (2) 13.3 What is the speed of the waves along the spring? (4) 13.4 Calculate the time taken for three complete wavelengths to pass a point in the spring. (5) 13.5 What is the wavelength of the waves along the spring if their frequency is in- creased to 6,0 Hz, without changing the tension (stretch) of the spring? (4) Question 14: Long questions Sunlight is a form of electromagnetic radiation. 14.1 What is an ‘electromagnetic wave’? (3) 14.2 What causes electromagnetic waves? (2) © Via Afrika » Physical Science 43  Topic 2 14.3 What is the speed of all electromagnetic waves in a vacuum? (1) 14.4 Assume that the sun is 1,5 × 108 km from the Earth. Calculate the time taken for sunlight to travel to the Earth. (5) Question 15: Long questions A gamma ray has a period of 2 × 10–24 s. 15.1 What is a gamma ray? (2) 15.2 Why is it dangerous for humans to be exposed to gamma rays? (2) 15.3 What is the frequency of this gamma ray? (3) 15.4 Calculate the wavelength of the gamma ray in metres. (4) Question 16: Long questions 16.1 What types of radiation are A and B? (2) 16.2 Which type of radiation can cause tanning of the skin? Give another use for this type of radiation. (4) 16.3 Which type of radiation next to A in the spectrum has a longer wavelength than A? Give one use for this type of radiation. (3) Question 17: Long questions Max Planck proposed that there is a relationship between the energy of a quantum of electromagnetic radiation and the frequency of the wave. 17.1 What is meant by a ‘quantum’ of electromagnetic radiation? (2) 17.2 What is a quantum of visible light called? (2) 17.3 What is the relationship between E and f as proposed by Max Planck? (2) 17.4 If we were to draw a graph of the energy of a quantum vs. the frequency of the quantum, what would the shape of the graph be? (2) © Via Afrika » Physical Science 44  Topic 2 Question 18: Long questions Calculate the energy content of a quantum of each of the following types of electromagnetic radiation: 18.1 a radio wave of frequency 600 kHz (4) 18.2 a green light wave of wavelength 500 nm in air (5) 18.3 an X-ray of wavelength 12 pm in air (5) Question 19: Long questions In a totally dark room, the human eye is only able to detect a flash of red light if the flash consists of at least 50 photons and if the flash is directed straight into the eye. Red light has a wavelength of 450 nm. Calculate the total minimum energy of a flash of red light that can be detected by the human eye. © Via Afrika » Physical Science 45  Topic 2 Answers to questions Answers Question 1: Multiple choice 1.1 B üüü 1.2 A üüü 1.3 C üüü 1.4 C üüü 1.5 D üüü 1.6 B üüü 1.7 D üüü 1.8 A üüü 1.9 C üüü 1.10 C üüü 1.11 D üüü 1.12 C üüü 1.13 A üüü Question 2: True / false 2.1 True üü 2.2 False. In a transverse wave, a pulse length is half as long as a wavelength. OR In a transverse wave, a wavelength is twice as long as a pulse length. üü 2.3 False. Amplitude is the maximum displacement from the position of rest. OR Wavelength is the distance between two consecutive points that are in phase. üü 2.4 False. An increase in frequency of a sound wave and a simultaneous increase in amplitude will cause a note that is louder and has a higher pitch. üü 2.5 False. The energy of electromagnetic radiation is directly proportional to the frequency of the radiation. üü Question 3: One-word answers 3.1 violet ü 3.2 rarefaction ü 3.3 infrared ü 3.4 wavelength ü 3.5 photon ü © Via Afrika » Physical Science 46  Topic 2 Answers to questions Question 4: Matching pairs 4.1 Cü 4.2 Eü 4.3 Bü 4.4 Dü 45 Fü Question 5: Long questions 5.1 movement from B to C to B to A and back to B üü 5.2 position B üü 5.3 number of oscillations per second üü 5.4 horizontal distance from B to A (or B to C) üü 5.5 time taken for one oscillation üü Question 6: Long questions 6.1 line through points AHCEG üü 6.2 A and E (or B and F) (or C and G) üü 6.3 B (or F) üü 6.4 distance BH üü 6.5 A and C (or B and D) (or C and E) (or D and F) (or E and G) üü 6.6 straight-line distance AE (or BF) (or CG) üü Question 7: Long questions 7.1 Frequency is the number of wavelengths that pass a point per second. If 10 pass in 2 seconds, 5 must pass in one second. f = 5 Hz üü 7.2 T = 1/fü = 1 /5 ü = 0,2 s ü 7.3 Distance BF is one wavelength.  = 300 mm = 0,3 m ü v = fü = 5 × 0,3 ü = 1,5 m.s–1 ü © Via Afrika » Physical Science 47  Topic 2 Answers to questions Question 8: Long questions 8.1 One oscillation of a particle produces one wavelength. So one wavelength passes a point in 0,4 s. Eight wavelengths pass in 8 × 0,4 s ü = 3,2 s. ü 8.2 Amplitude is distance from rest position to crest = 12,5 mm = 0,0125 m. üü 8.3 0,4 s üü 8.4 The given distance is for 2 wavelengths.  = 0,68 / 2 = 0,34 m ü 8.5 f = 1/Tü = 1 / 0,4 ü = 2,5 Hz ü 8.6 v = fü = 2,5 × 0,34 üü = 0,85 m.s–1 ü Question 9: Long questions 9.1 constructive and destructive ü interference ü 9.2 flat water üü (or areas of destructive interference) 9.3 These are areas where crests and troughs meet, and cancel out to produce flat water. üü Question 10: Long questions 10.1 longitudinal wave üü 10.2 Fix one end of the spring or have the friend hold it still. Stretch the spring. ü Hold the other end of the spring and push it forward and backwards rapidly and continuously üü along the straight line of the spring. ü 10.3 It is the distance between two consecutive crests üü (or two consecutive troughs or two consecutive points that are in phase). Question 11: Long questions 11.1 v = f  = v / f üü = 340 / 500 ü = 0,68 m ü 11.2  = v/f = 3 × 108 / 5 × 1014 üü © Via Afrika » Physical Science 48  Topic 2 Answers to questions = 6 × 10–7 m ü 11.3 6 × 10–7 m = 600 nm ü Question 12: Long questions 12.1 For the demonstration you will need an electric bell or buzzer with a switch, a suitable power supply, and a glass jar that can be connected to a vacuum pump that is able to pump the air out of the jar to produce a near vacuum. Connect the bell or buzzer to the power supply. ü Place it in the jar and switch on. You will hear the bell ringing loudly. ü Switch on the vacuum pump to extract air. ü The sound gets fainter and fainter. In a total vacuum, the sound would be inaudible. ü 12.2 The moon does not have an atmosphere, ü so no sound can be heard on the moon. ü v 340ü 12.3 v = f ü = = f 156ü = 2,18 m ü 1 1 12.4 T = ü= f 256ü = 3.9 × 10–3 sü (or 0,0039 s) 12.5 Ultrasoundü 12.6 Used in medicine to observe internal organs such as a baby in the womb.üü OR Used in industry to detect cracks in metals. Question 13: Long questions 13.1 Transverse wave ü 13.2 f = 2 Hz, so two wavelengths pass a point in one second. Therefore, in three seconds, six wavelengths pass a point. üü 13.3 v = fü = 2 × 0,45 üü = 0,9 m.s–1 ü 13.4 T = 1/fü = 1 /2 ü = 0,5 s ü One wavelength passes in 0,5 s, so three wavelengths pass in 1,5 s. üü 13.5 If the tension of the spring does not change, speed of the wave is constant. Frequency and wavelength are inversely proportional to each other. ü So, if © Via Afrika » Physical Science 49  Topic 2 Answers to questions frequency is made three times larger, wavelength must be made three times smaller.ü So the wavelength is 0,15 m. üü OR  = v/fü = 0,9 / 6 üü = 0,15 m ü Question 14: Long questions 14.1 A changing electric field produces a changing magnetic field, which in turn produces a changing electric field. An electromagnetic wave is a transverse wave consisting of electric and magnetic fields at 90° to each other. üü The crests and troughs represent points where the electric or magnetic fields are strongest. ü 14.2 Accelerating charges produce electromagnetic pulses. ü A continuous electromagnetic wave is produced by vibrating charges, as in alternating current. ü 14.3 3 × 108 m.s–1 ü 14.4 First convert to SI units. 1,5 × 108 km = 1,5 × 1011 m ü time = distance / speed ü = 1,5 × 1011 / 3 × 108 üü = 500 s ü (This is 8 minutes and 20 seconds.) Question 15: Long questions 15.1 Gamma rays are very high-frequency and high-energy electromagnetic radiation emitted by radioactive material. üü 15.2 They can destroy human tissue and cause cancer. üü 15.3 f = 1/Tü = 1 / 2 × 10–24 ü = 5 × 1023 Hz ü 15.4 c = f  = c/fü = 3 × 108 / 5 × 1023 ü = 6 × 10–16 m ü © Via Afrika » Physical Science 50  Topic 2 Answers to questions Question 16: Long questions 16.1 A – infrared ü B – X-rays ü 16.2 ultraviolet ü Certain chemicals fluoresce in ultraviolet light. ü For example, chemicals in washing powder will fluoresce under the ultraviolet light from the sun, making garments look whiter than they actually are. üü 16.3 microwaves ü In microwave ovens, water in the foodstuffs are made to vibrate faster by the microwaves, thereby getting hotter. üü Question 17: Long questions 17.1 ‘Quantum’ means a discreet amount or ‘package’. So, the radiation is not in con- tinuous waves, but small packages of energy, each made up of electromagnetic waves. üü 17.2 photon üü 17.3 E is directly proportional to f. This means that if f is doubled, E is doubled. üü 17.4 a straight line through the origin üü Question 18: Long questions 18.1 f must be expressed in Hz. 600 kHz = 6 × 105 Hz ü E = hf ü = 6,63 × 10–34 × 6 × 105 ü = 3,98 × 10–28 J ü  must be expressed in metres. 500 nm = 500 × 10–9 m ü E = hc /  ü (6,63 × 10–34) × (3 × 108) ü = 500 × 10–9 ü = 3,98 × 10–19 Hz ü  must be expressed in metres. 120 pm = 120 × 10–12 m ü E = hc /  ü (6,63 × 10–34) × (3 × 108) ü = 120 × 10–12 ü = 1,66 × 10–15 J ü © Via Afrika » Physical Science 51  Topic 2 Answers to questions Question 19: Long questions First calculate the energy of one photon of red light. 450 nm = 450 × 10–9 m ü E = hc /ü (6,63 × 10–34) × (3 × 108) ü = 450 × 10–9 ü = 4,42 × 10–19 J ü Minimum number of photons = 50 Minimum energy of the flash = (4,42 × 10–19) × 50 ü = 2,21 × 10–17 J ü © Via Afrika » Physical Science 52  Topic 3 Magnetism and electricity Overview © Via Afrika » Physical Science 53  Topic 3 Summary 1 Magnetism 1.1 Magnetism A magnetic field is a region in space in which a magnet or ferromagnetic substance (iron, nickel or cobalt) will experience a force. The poles of a magnet are at the two ends of the magnet. The magnetic force is strongest at the poles. If a magnet is cut in half, each half will be a magnet with a north pole at one end and a south pole at the other. If a magnet is suspended at its centre so that it can turn freely, it will be affected by the magnetic field of the earth and settle in a north-south direction. The pole of a magnet that points towards the Earth’s north pole is called the north-seeking pole (or simply the north pole) of the magnet. Like poles of two magnets repel, unlike poles attract. So north repels north, but north attracts south. A compass is a magnet that is free to turn at its centre. A magnet is surrounded by a magnetic field – a region in which magnetic materials such as iron will experience a force. A compass is used to show the direction of a magnetic field. A magnetic field line shows the shape of the field and the direction that the north pole of a compass will point when placed in the field. Magnetic field lines point from north to south of a magnet. The more closely spaced the field lines are at a point, the stronger is the field at that point, that is, the stronger the force will be on a magnetic object. Field lines never cross. They surround a magnet in three dimensions. For simplicity, we draw field lines in two dimensions only. The geographical north and south poles are the points around which the Earth rotates. © Via Afrika » Physical Science 54  Topic 3 The magnetic field of the Earth is similar to that of a bar magnet, with poles at the magnetic north and magnetic south of the Earth. The imaginary bar magnet inside the Earth must have its north pole at the south geomagnetic pole. The angle between the geographic north pole and the geomagnetic north pole is 11,5°. The magnetic field of the Earth protects the Earth from harmful ions of hydrogen and helium, as well as electrons emitted by the sun (solar wind). These are deflected to the poles by the magnetosphere, where they collide with the atmosphere and produce an aurora. 2 Electrostatics 2.1 Two kinds of charge The property of particles in atoms that enables them to attract and repel is called charge. There are only two types of charge. Like charges repel, unlike charges attract. Charges are called positive and negative because when the two types come together they cancel out to produce zero charge. © Via Afrika » Physical Science 55  Topic 3 Atoms are made up of a central nucleus comprised of positively charged protons and neutral neutrons. The nucleus is surrounded by a number of negatively charged electrons that are much smaller than protons. Objects become charged when electrons are either removed from them or added to them. This can be done by rubbing two materials together, called tribo-electric charging. An object that has an equal number of positive and negative charges is neutral. Conductors allow a flow of charge through them. Conductors contain charges that are free to move. Insulators do not allow a flow of charge through them. They do not contain charged particles that are free to move. An electric field is a region in space in which an electric charge will experience a force. All charged objects are surrounded by electric fields. An electric field line is a line drawn with an arrow to show the direction in which a positive charge will experience a force if placed in the field. Attraction of a Attraction of an insulator. Attraction of water. H2O conductor. The atoms become polarised. molecules are polarised. © Via Afrika » Physical Sci