Physics Eng 1 Standard X PDF 2019
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2019
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This textbook is for standard X physics. It covers various topics like electric currents, including their effects, and includes diagrams and practical examples. It promotes understanding through experiments and encourages critical thinking.
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Standard X Part-1 NT-497-1-PHYSICS-10-E-VOL.1 Government of Kerala Department of General Education State Council of Educational Researc...
Standard X Part-1 NT-497-1-PHYSICS-10-E-VOL.1 Government of Kerala Department of General Education State Council of Educational Research and Training (SCERT) Kerala 2019 THE NATIONAL ANTHEM Jana-gana-mana adhinayaka jaya he Bharatha-bhagya-vidhata, Punjab-Sindh-Gujarat-Maratha Dravida-Utkala-Banga Vindhya-Himachala-Yamuna-Ganga Uchchala-Jaladhi-taranga Tava subha name jage, Tava subha asisa mage, Gahe tava jaya gatha. Jana-gana-mangala-dayaka jaya he Bharatha-bhagya-vidhata, Jaya he, jaya he, jaya he, Jaya jaya jaya jaya he! PLEDGE India is my country. All Indians are my brothers and sisters. I love my country, and I am proud of its rich and varied heritage. I shall always strive to be worthy of it. I shall give my parents, teachers and all elders respect, and treat everyone with courtesy. To my country and my people, I pledge my devotion. In their well-being and prosperity alone lies my happiness. State Council of Educational Research and Training (SCERT) Poojappura, Thiruvananthapuram 695012, Kerala Website : www.scertkerala.gov.in, e-mail : [email protected] Phone : 0471 - 2341883, Fax : 0471 - 2341869 Typesetting and Layout : SCERT Printed at : KBPS, Kakkanad, Kochi-30 © Department of Education, Government of Kerala Dear students, You were provided with opportunities to observe your surroundings and engage in simple experiments and investigative activities in earlier classes. The classroom experience, undoubtedly, might have helped you to record the information systematically and assimilate ideas through discussion and analysis. While understanding the scientific approach, there should also be the attitude to take forward the skills to apply them in day-to-day life. Moreover, an eco-friendly perspective must be adopted too. All these, through direct experiences, enquiry and understanding preferably. This textbook presents ideas in accordance with this. 'Samagra', the education portal and technology enabled QR Code printed textbooks would definitely make your learning activity in classrooms easy and joyful. The National Skills Qualifications Framework, the current relevance of Disaster Management and the possibilities of ICT have also been considered while modifying the textbook. Go ahead, thinking, asking questions, approaching ideas critically and quizzing with teachers and friends. Make learning a joyful experience. Regards, Dr. J. Prasad Director, SCERT CONSTITUTION OF INDIA Part IV A FUNDAMENTAL DUTIES OF CITIZENS FUNDAMENTAL ARTICLE 51 A Fundamental Duties- It shall be the duty of every citizen of India: (a) to abide by the Constitution and respect its ideals and institutions, the National Flag and the National Anthem; (b) to cherish and follow the noble ideals which inspired our national struggle for freedom; (c) to uphold and protect the sovereignty, unity and integrity of India; (d) to defend the country and render national service when called upon to do so; (e) to promote harmony and the spirit of common brotherhood amongst all the people of India transcending religious, linguistic and regional or sectional diversities; to renounce practices derogatory to the dignity of women; (f) to value and preserve the rich heritage of our composite culture; (g) to protect and improve the natural environment including forests, lakes, rivers, wild life and to have compassion for living creatures; (h) to develop the scientific temper, humanism and the spirit of inquiry and reform; (i) to safeguard public property and to abjure violence; (j) to strive towards excellence in all spheres of individual and collective activity so that the nation constantly rises to higher levels of endeavour and achievements; (k) who is a parent or guardian to provide opportunities for education to his child or, as the case may be, ward between age of six and fourteen years. 1. Effects of Electric Current.............. 07 2. Magnetic Effect of Electric Current 33 3. Electromagnetic Induction........... 45 4. Reflection of Light......................... 79 Certain icons are used in this textbook for convenience For further reading (Evaluation not required) ICT possibilities for making concepts clear Let us assess Extended activities NSQF All the devices here work using electric current. How do they give different forms of energy! Have you also felt the same doubt? Some electrical devices are shown in the house of the child. What are they? Let's try to write them down. Electric bulb Electric fan It is electrical energy that is given to the devices. But don't they give us different forms of energy? Write down the energy changes in them with respect to their use. $ - X Device Use Energy change $ Electric bulb......................................................... →....................... $ Induction cooker To get heat Electrical energy → Heat $ Storage battery (while charging)......................................................... →....................... $ Mixie......................................................... →....................... $............................................................................................ →....................... $............................................................................................ →....................... Table 1.1 It is clear from the table that electrical energy can be transformed into different forms of energy. The useful form of energy into which a device converts electrical energy, is considered as the effect of electric current on that device. We are familiar with so many electrical devices in our daily life. Write down in your science diary the effect of electric current on each of them. You might have studied in your chemistry class the chemical effect of current. Now we shall learn more about the heating and the lighting effects of electricity. Among those we use in daily life, which are the devices that give heating effect of electric current? Electric iron How does electrical energy change into heat energy in such devices? Lets do an experiment. Materials required: - A nichrome wire of approximate length 5 cm - 6 V storage battery - Connection wires Construct a circuit as shown in Fig. 1.1 R Nichrome wire 6V S Fig. 1.1 How does the nichrome wire become red hot while passing electricity through the circuit? Analyse this based on the concept that energy can neither be created nor destroyed. It can only be converted from one form to another (Law of Conservation of Energy) In this case which form of energy was converted into heat energy? How does this energy change occur? Lets analyse by examining the current and voltage in the circuit. S Fig. 1.2 We can measure the voltage between the ends of the resistor R (nichrome wire) using a voltmeter V and the current through it, using an ammeter A. If the ammeter shows a current I ampere on applying a potential difference V across the resistor of resistance R Ω , Q Current I = t Then, the charge that flows through the conductor in t second, Q =........ coulomb. The potential difference between two points will be one volt if one joule of work is done in moving one coulomb of charge from one point to the other. $ - X One joule of work is required to move one coulomb of James Prescott Joule charge under one volt potential difference. Hence the work and Joule's Law W to be done to move one coulomb of charge under a potential difference V will be, W = V joule. If so, the work to be done to move a charge Q under a potential difference V is W = QV. The work required for moving the electric charge through the conductor is done by the battery connected to the circut. The power P supplied W by the battery to the circuit in a time t second is P =. t On substituting the equation of work in this we get V×Q P = t Q I= t ie, P = VI. Therefore the energy supplied by the battery to the circuit in t second = Pt = VIt. The electrical energy expended by the battery in the circuit containing the nichrome wire is converted into heat. Therefore H = VIt The heat is developed since a current is available in the circuit in accordance with the voltage applied. If so why did the nichrome wire in the circuit alone become red hot? Lets examine the influence of resistance in changing the electrical energy into heat energy. According to Ohms Law, V = IR. On substituting this in the equation H = VIt ! "#$" % ! "2# From this it can be understood why the nichrome wire alone becomes red hot. This process by which heat is developed in a circuit on passing current through it is known as the Joule Heating or Ohmic Heating. Havent you understood the factors influencing the heat developed when a current passes through a conductor? Joule's Law $ % 4 $"% $#% $ % H ∝ IRt ∴ H = I Rt5 " # Complete the following table on the basis of Joules Law. Resistance of Intensity of Time for which Heat generated Change in conductor R (Ω) C - urrent I (A) -current flows t (s) I2Rt (J) Heat (H) 2R I t 2 IRt Twice (2H) R 2I t...................................... R/2 I t...................................... R I/2 t...................................... R I 2t...................................... R I t/2...................................... Table 1.2 Analyse the table and find out the factor that influences heat the most. Dont you now understand how the change in current, resistance and the time for which electricity flows influence the amount of heat developed? & ' ( ' & $"% $#% $ % )* + ,--& + --& . #/ 0 + )* 1 ' .#/23 0 + # ( 3 + )* 212 P Q R S 1 + − − + + 6 Fig. 1.3 2 1 + 2 $ - X Joules Law is useful in devices that make use of heating effect of electricity. Lets solve some mathematical problems which are related to Joules Law. How much will be the heat developed if 0.2 A current flows through a conductor of resistance 200 Ω for 5 minute? ∴ !"2# # !,--Ω !$- ,%2 × ,-- × 6-- " !- ,) !,7-- !8 × 9- !6-- ∴ Heat generated = 2400 J If 4.2 J is one calorie then H =.. calorie H = I2Rt is used to find out the heat developed when current flows through a conductor. Lets try to write down the equation in some other forms as well. According to Ohms Law, I = V/R. If we substitute this in the equation according to Joules Law H = I2Rt, we get H = (V/R)2Rt 2 ⎛V⎞ H = ⎜ ⎟ Rt ⎝R⎠ =...................... Lets find out the heat developed in 3 minute by a device of resistance 920 Ω working under 230 V V = 230 V Try to solve the problem R = 920 Ω in another way t = 3 × 60 s V = 230 V, R = 920 Ω V On using the given values I= R =.................... V2 t H= H = I2Rt R 2302 ×3×60 = 920 =........................... H = 10350 J H =.........................J Is there any difference in the amount of heat energy thus obtained? Note down in the science diary how this problem can be solved using the relation, H = VIt. Lets calculate the heat developed when 3 A current flows through an electric iron box designed to work under 230 V. Which equation will help us to solve the problem easily? Solve the problem. Details of two electric heaters are given below. How much will be the heat developed if they are made to work for 5 minute each? Heater - A Heater - B Working voltage : 230 V Working voltage : 230 V Resistance : 1150 Ω Resistance : 460 Ω Working time : 5 minute Working time : 5 minute V2 t V2 t H = H = R R 2302 ×300 2302 × 300 = = 1150 460 = 13800 J = 34500 J Table 1.3 Why does the heater having low resistance get heated more? In which way does the change in resistance influence the heat developed? Find out the current in the heaters A and B and compare the heat developed. How do the resistors bring about a change in the current in the circuit? Lets take a look at how the voltage and current changes when resistors are arranged in different ways in circuits. Two different circuits which can be constructed using a 6 V- 2 A battery, 3 W-6 V bulbs and a switch are given (Fig 1.4). Construct these circuits and operate it. Write down the answers based on your observations. 3W B B 3W 6V Fig. 1.4 () $ - X B B 3W 3W 6V Fig. 1.4 ( ) In which circuit does the bulb glow with high intensity? Remove one bulb from each circuit. What do you observe? In fig1.4 (a)................................... In fig 1.4 (b)................................... Why do the bulbs in Fig1.4 (a) glow with maximum brightness? Draw a suitable circuit with ammeter and voltmeter in the circuit replacing the bulbs by 1 Ω, 2.2 Ω resistors. Compare the circuit you have drawn with the one given below and construct it properly. Record the readings in the table. 2 2Ω 1Ω 3V Fig. 1.5 () 2 2Ω 1Ω 3V Fig. 1.5 ( ) Voltage obtained Current in Effective Resistance in resistance (V) resistances (I) (by analysing the current) Mode of 2.2 Ω 1Ω Effective 2.2 Ω 1Ω " : connection of voltage resistances 2 2Ω 1Ω 2 2Ω 1Ω Table 1.4 ) + (ü) Mode of Effective Voltage obtained Current connection of Resistance in each through each resistances resistance resistance 2 2Ω 1Ω : : : 2 2Ω : : : 1Ω Table 1.5 When a circuit is completed by connecting the resistors one after the other, it is called series connection. When resistors are connected like this, the effective resistance increases. R R I Fig. 1.6 When resistors are connected in series, the potential difference gets divided. V = V +V The current through each resistor will be the same. Hence V = IR , V = I R In a series circuit the voltage across the higher resistane will be greater. According to Ohms Law, V = IR. Here R indicates the effective resistance. Hence $ - X Now our journey is Colour Code impossible. The value of resistance of carbon resistors available in the market has their resistance directly marked on them or indicated by colour codes. Usually rings of four different colours are used. The first two rings indicate the two digits, the third one indicates the number of zeroes and the fourth ring indicates tolerance Oh, We have to cross (deviation). Silver ; 10%, gold three bridges to reach the ; 5%, and if there is no fourth other side. Very difficult. Just as the resistors in line, then ; 20% deviation will series. be there. IR = IR + I R IR = I (R + R) For example, if the first two rings are red and violet, then the first two R = R + R digits are 2 and 7. The third one Effective resistance is the sum of the resistance of all the denotes the number of zeroes. If resistors when they are connected in series. If the resistors this is orange, then there are three are of the same value, then the effective resistance can be zeroes. Now the value is 27000 Ω. obtained by multiplying the resistance of a resistor with If the silver ring is also considered the number of resistors. then the value = ," White 9 9 Since R is the effective resistance, V V V By Ohms Law R = R + R 1 2 ⎛1⎞ ⎛ 1 1 ⎞ V⎜ ⎟=V⎜ + ⎟ ⎝R⎠ ⎝ R1 R 2 ⎠ 1 1 1 = + R R1 R2 R 1R 2 R + R 1 2 r n The current through each resistor is different. It gets Ω Ω NT-497-2-PHYSICS-10-E-VOL.1 V = 6V R = R + R = 4+2=6Ω V R = I 6 6 = I 6 I = =1A 6 $ - X Wow! There are three parallel bridges. Sure to have a smooth journey! Even if one bridge breaks down, the journey will not be affected. But the difficulties have increased. $ What is the current if 12 Ω and 4 Ω resistors are connected in parallel and 12 V potential difference is applied? = 12 Ω, R= 4 Ω, V = 12 V V = 12 V 1 1 1 R 1R 2 = + R = R +R R R1 R2 1 2 1 1 1 4 + 12 16 12 × 4 = + = = = R 12 4 12 × 4 48 12 + 4 OR 48 48 R= =3Ω = = 3Ω 16 16 V 12 V 12 I = = = 4A Current I = = = 4A R 3 R 3 $ 10 resistors of 2 Ω each are connected in parallel. Calculate the effective resistance. When the voltage is constant, current will decrease with an increase in resistance. Wont this help you in explaining why the heat decreases even after increasing the resistance? We can bring about change in current and voltage by connecting resistors in different ways. Now you would have understood why it is stated in Joules Law that heat is directly proportional to resistance only when the current and time are constant? ! ! "# $ Electric heating appliances are instruments that make use of the heating effect of electricity. Electrical energy is converted into heat energy in them. Fig 1.8 A few heating appliances are shown in the figure. Examine any one of them and answer the following questions. Record the answers in the science diary. Name the part in which electrical energy changes into heat energy. Which material is used to make this part? What are the peculiarities of such substances? high resistivity ability to remain in red hot condition for a long time without getting oxidised $ - X Heating coils are made of nichrome. Nichrome is Appliances without an alloy of nickel, chromium and iron heating coil Lets see what advantages of nichrome are made use of in electric heating appliances. High resistivity High melting point Ability to remain in red hot condition for a long time without getting oxidised. Microwave oven and induction cooker are appliances which do " not use a heating coil. In a Safety fuse is a device that works on the heating effect microwave oven, microwaves of electric current. Lets see how it works. are used and induction cooker uses eddy currents. Fuse wire, an alloy of tin and lead, is the main part of safety fuse. Alloys are used to make fuse wire. Fuse wire has a relatively low melting point. In each circuit the fuse wire should be used in accordance with the current flowing through it. Which are the circumstances that cause high electric current, leading to the melting of fuse wire? How is the fuse wire connected to a circuit? In Fig 1.9 series/ parallel? Short Circuit and You know that according to Joules Law, more heat Overloading will be produced when electric current is increased. " What happens to the fuse wire due to this? When heat is generated, why does the fuse wire melt? ? ) When the fuse wire melts, the circuit is broken. What happens to the current in the circuit? Why is the fuse used in a circuit called safety fuse? Explain. During the entire time of the passing of current through a circuit, a small amount of heat is generated in the fuse wire. But this heat will be transmitted to the surroundings. When the current that flows into the circuit exceeds the permissible limit, the heat generated becomes excessive. Since more heat is generated in unit time than the heat transmitted, the fuse wire melts. Safety fuse is a device which protects us and the appliances from danger when an excess current flows through the circuit. Is the current passing through different circuits the same? Intensity of electric current differs from one Gauge appliance to another. Hence fuse wires of appropriate amperage should be selected. @ ) When a fuse wire is included in a household wiring, what + are the precautions to be taken? Lets see. The ends of the fuse wire must be connected firmly at appropriate points. The fuse wire should not project out of the carrier base. Amperage ) $)% ! % & 4 ) You might have noticed the marking of 500 W on an + electrical appliance. What does it indicate? An electrical appliance works by making use of electrical energy. Hence it has a power. You have studied in the earlier class that power is the work done per unit time. The amount of energy consumed by an electrical appliance in unit time is its power. ⎛W⎞ Power is calculated using P = ⎜ ⎟ ⎝ t ⎠ What is the unit of power? According to Joule's Law, the heat generated (H) in an electrical circuit in an interval of time t second or the work done is H = I2Rt Then, how is the power calculated? $ - X Work done H = I2Rt Time = t Work H Power, P = = time t I 2 Rt Power t V By Ohms Law, I = R P = IR 2 ⎛ V⎞ V2 = ⎜⎝ ⎟⎠ R = R R V2 Thus, P = R V If R = what will be P? I P = IR = I ×..... =..... The unit of electric power is watt (W). An appliance of power 540 W is used in a branch circuit. If the voltage is 230 V, what is its amperage? Wattage W Amperage = = Voltage V W 540 "! ! !, 67)≈ , 7) V 230 A heating appliance has a resistance of 115 Ω. If 2 A current flows through it, what is the power of the appliance? # ! 8Ω " ! ,) ! "2# ! ,2× 8 !79-1 A current of 0.4 A flows through an electric bulb working at 230 V. What is the power of the bulb? ' ( Filament lamps were in wide use in the early days. Observe the parts of a filament lamp shown in Fig 1.10. ! Fig 1.10 Incandescent lamps In normal voltages, the filament becomes white hot and gives out light. Such bulbs are the incandescent (glowing with heat) lamps. Filaments made of the metal tungsten are used in them. Tungsten can become white hot and emit white light for a long time. In order to avoid oxidation of tungsten, the bulb is evacuated. Vaporisation can be reduced by filling some inert gas at low pressure inside the bulb. Nitrogen is usually used for this purpose now. Why is the bulb filled with an inert gas/ nitrogen? Why Nitrogen? ) What properties of tungsten make it suitable for + being used as a filament? / high resistivity ( high melting point high ductility " ability to emit white light in the white hot condition $ - X Nichrome is not used as filament in incandescent lamps. Why? Touch a filament lamp after it has been lit for a short period of time. What do you feel? A major part of the electrical energy supplied to an incandescent lamp is lost as heat. Hence the efficiency of these devices is less. Haven't you understood that a major part of the electricity supplied to an incandescent lamp for obtaining light is lost as heat? By now it may be clear to you why the use of incandescent lamps is to be restricted. What are the other types of lamps working on electricity? List them. Discharge lamp Fluorescent lamp ) ( % " # #$ Fig 1.11 Discharge lamps are glass tubes fitted with two electrodes. They emit light as a result of discharge of electricity through the gases filled in tubes. When a high potential difference is applied the gas molecules get excited. Excited atoms come back to their original states for attaining stability. During this process the energy stored in them will be radiated as light. Depending on the difference in the energy levels lights of different colours and other radiations are emitted. What are the advantages of using discharge lamps instead of incandescent lamps? What are the factors to be considered when you select a bulb? Which are the lamps that are mostly used? Why? LED bulbs are devices that give more light than discharge lamps and incandescent lamps. They work using low power. What are their peculiarities? '!) ** +' ( , , **- LEDs are Light Emitting Diodes. As there is no filament, there is no loss of energy in the form of heat. Since there is no mercury in it, it is not harmful to environment LED Bulb Fig 1.12 '!).* (Construction, repair, reuse and disposal) It is the research for high energy efficient and less polluting bulbs that led to the invention of LED bulbs. LED bulbs are more efficient than other bulbs. Low power consumption, high efficiency and high longevity are the advantages. Production of LED bulbs at low cost must be encouraged to enhance their use. At the same time we should know how to do minor repairing of the bulb to facilitate $ - X its reuse and also the scientific methods of its disposal to minimise the related environment problems. Let's do some activities to understand about LED bulbs. Let's familiarise with the parts of the bulb. Part of on LED bulb Use Part of the LED bulb Use Base unit E22 This is the metallic Power Supply Function of this is to part that connects the board (LED convert AC into DC bulb to the holder driver) and supply necessary output voltage ( The same board can be used for 5W, 7W and 9 W bulbs.) Heat sink The part close to the Printed Circuit LEDs are fixed on base unit of the bulb. Board (LED Chip this board. In this the It is an arrangement Board) positive and negative for absorbing heat polarities are marked. from the base. Base plate Metal plate that fixes it to the holder. Back conductor Screws for fixing Diffuser cup This is the part from wires from LED which light comes out Screws. drive to the base unit. of the bulb. Figure Showing a Completed LED Bulb Circuit Other accessory tools required to construct an LED bulb Insulation tape Pliers Heat sink compound Wire stripper Soldering iron Solder Lead Soldering wax Fix the base unit by punching it on to the heat sink Cover the power supply board using insulation tapes in such a way that the input and output supply wires will be visible out but will not get covered with dust or moisture. Fix the wires seen on the input part of the power supply board to the back conductor, by passing it through heat sink and terminal holes. Fix the red wire in the output into the part marked positive in the board and the black wire into the negative marking. Apply heat sink compound at the back of the LED Printed Circuit Board and then fix it on the base plate. Press and close the heat sink by using the diffuser cup. Make sure that the LED bulb thus made emits light when fixed to the bulb holder. An LED bulb is a combination of many LEDs connected in series. The bulb will fail to emit light if any one LED is damaged or if the contact of any one LED is lost. LED bulb will not emit light if the rectifier or load resistor or filter capacitor is damaged. Even a minor damage in an LED bulb will lead to complete failure in the working of the bulb. How can these errors be rectified? $ - X /( 0 % '!) ** Examine a damaged LED bulb and find out the following parts (Rectifier, Load resistor, Filter capacitor, LED Chip, Heat Sink) '1 2 &( ( 3, % '!) **4 ) ) ) ) ) ) ) ) / ) 0 ) ) / ) $*+ ) A ) B $ Open a non functioning bulb and examine each part using a multimeter to know whether the parts are functioning or not. Find out which of the following parts are damaged in an LED bulb and replace them with new ones. Rectifier Load resistor Filter capacitor LED Chip & ( '!) ** * ,% , "5 Segregate the plastic, electronic and metal components of LED bulb and transfer them to their respective disposal units. Dont you have to enhance the use of LED bulbs which are environment friendly and suitable for energy conservation? Energy saved is equivalent to energy produced Let us assess 3. Fuse wire is to be used by understanding the amperage correctly. Write down the amperage of the fuse wires that are currently available in the market. 2. 0.5 A current flows though an electric heating device connected to 230 V supply. (a) the quantity of charge that flows through the circuit in 5 minute is (i) 5 C (ii) 15 C (iii) 150 C ( iv) 1500 C (b) How much is the resistance of the circuit? (c) Calculate the quantity of heat generated when current flows in the circuit for 5 minute. (d) How much is the power of the heating device connected to the circuit if we ignore the resistance of the circuit wire? 3. According to Joules Law the heat generated due to the flow of current is H = I2Rt. Will the heat developed increase on increasing the resistance without changing the voltage? Explain. 4. The table shows details of an electric heating device designed to work in 230 V. Complete the table by calculating the change in the heat and power on changing the voltage and resistance of the device. Analyse the table and answer the following questions. Operating Resistance of Current flowing Heat generated Power given Reason for voltage the device (R) in the device per second by the device the change I = V/R Heat, H = V × I × t P = V × I or P = H/t in power 230 V 57.5 Ω 4A 920 J 920 W 230 V 115 Ω ------------------ ------------------ ------------------ 230 V 230 Ω ------------------ ------------------ ------------------ 115 V 57.5 Ω ------------------ ------------------ ------------------ 460 V 57.5 Ω ------------------ ------------------ ------------------ (a) How does the voltage under which a device works affect its functioning? $ - X 8b) What change happens to power on increasing the resistance without changing the voltage? (c) What change is to be brought about in the construction of household heating devices inorder to increase their power? 5. (a) Complete the table based on the amperage of the fuse wire. Electrical device Operating Power of Current The amperage voltage (V) the device (P) through the circuit of the fuse to be I = P/V used in the circuit (A) Water heater 230 V 4370 W 19 A 20 A Air conditioner(AC) 230 V ------------------ 14.5 A ------------------ Television (LED - TV) 230 V 57.5 W ------------------ ------------------ Computer (Laptop) 230 V ------------------ 0.125 A ------------------ b) The amperage of the fuse wire used in a circuit that works on 230 V is 2.2 A. If so the power of the device is (i) less than 300 W (ii) 300 W to 500 W (iii) between 500 W and 510 W (iv) more than 510 W 6. A 230 V, 115 W filament lamp works in a circuit for 10 minute. (a) What is the current flowing through the bulb? (b) How much is the quantity of charge that flows through the bulb in 10 minute? 7. An electric heater conducts 4 A current when 60 V is applied across its terminals. What will be the current if the potential difference is 120 V? 8. Three resistors of 2 Ω, 3 Ω and 6 Ω are given in the class. (a) What is the highest resistance that you can get using all of them? (b) What is the least resistance that you can get using all of them? (c) Can you make a resistance 4.5 Ω using these three? Draw the circuit. >. A girl has many resistors of 2 Ω each. She needs a circuit of 9 Ω resistance. For this draw a circuit with the minimum number of resistors. 10. If a bulb is lit after rejoining the parts of a broken filament, what change will occur in the intensity of the light from the lamp? What will be the change in the power of the bulb? 11. Which of the following does not indicate the power of a circuit? (a) I2R (b) VI (c) IR2 (d) V2/R 12. How much will be the power of a 220 V, 100 W electric bulb working at 110 V? (a) 100 W (b) 75 W (c) 50 W (d) 25 W 13. Which of the following should be connected in parallel to a device in a circuit? (a) voltmeter (b) ammeter (c) galvanometer 14. When a 12 V battery is connected to resistor, 2.5 mA current flows through the circuit. If so what is the resistance of the resistor? 15. If 0.2 Ω,0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω resistors are connected to a 9 V battery in parallel, what will be the current through the 12 Ω resistor? 16. How many resistors of 176 Ω should be connected in parallel to get 5A current from 220 V supply? a) 2 b) 3 c) 6 d) 4 17. Depict a figure showing the arrangement of three resistors in a circuit to get an effective resistance of (i) 9 Ω (ii) 4 Ω Extended activities 1. Analyse and describe the working of a microwave oven. 2. How does an arc lamp help in rescue operations? 3. With the help of teachers and the Internet find out the following $ - X 1a) What is the percentage of nickel, chromium and iron in Nichrome? (b) How much is the melting point of nichrome in degree celsius? (c) How much is the resistivity of Nichrome? (d) Does the result of your observation justify the use of nichrome as a heating element ? 4. Analyse the merits and demerits of the following lamps and find out which is best in the group. Justify your answers. (a) filament lamp (b) fluorescent lamp (c) arc lamp (d) CFL (e) LED bulb NT-497-3-PHYSICS-10-E-VOL.1 Soft $ - X How can you find out the polarity of these magnets using a magnetic compass? What are the main differences between the magnets in the picture? The magnetic field lines of the bar magnet and that of the electromagnets are similar. The presence of the magnetic field and the polarity can be understood using a magnetic compass. The magnetic strength/ magnetism of an electromagnet is temporary. The magnetic field around an electromagnet is created due to the flow of current through the coils in it. By this we can assume that a magnetic field will be developed when current passes through a straight conductor. Lets try to do a similar experiment that lead Oersted to this conclusion. Arrange a circuit above a pivoted magnetic needle in such a way that the part AB of the conductor is parallel and close to the magnetic needle, as shown in Fig 2.3 (a). ! " # $ % # &'( % - ) *+ , ) *+ , Switch on the circuit. Observe the direction in which the North Pole(N) of the magnetic needle deflects and complete the Table 2.1. When the direction of electric current is from A to B, what will be the direction of the electron flow through it? Effect of Electric Current. " above the North Pole (N) of the magnetic needle magnetic needle clockwise/anticlockwise ! . " / Direction of motion of No. Conductor below the North Pole (N) of the magnetic needle magnetic needle clockwise/anticlockwise ! % " 0 " 1 $ 2 / # % $ " " 1 / Physics $ Standard - X / 46 . 3 $ 4 / 1 #!# !!# 5" 4 / / + , 4 ( % &7) ( ) 8 / 8 $ What we have understood is the Right Hand Thumb Rule of James Clark Maxwell. Imagine you are holding a current carrying conductor with the right hand in such a way, that the thumb points in the direction of the current. The direction in which the other fingers encircle the conductor gives the direction of the magnetic field. The same rule is also known as Right Hand Screw Rule. If a right hand screw is rotated in such a way that its tip advances along the direction of the current in the conductor, then the direction of rotation of the screw gives the direction of the magnetic field around the conductor. Magnetic Effect of Electric Current / $ $ 5" 8 / 0 # C A B K 4 / $ / 1 / / $ ! / $ Lets see how the number of turns of the coiled conductor and the intensity of current affect the magnetic field. Keep a current carrying circular conductor vertically in the North South direction (Fig.2.7). The magnetic field produced as a result will be in the East West direction. Draw a perpendicular bisector to the line joining the points A and B. This line passes through the centre of the coil. Move the compass along this line in both directions away from the centre. When the magnetic effect of the coil vanishes, the magnetic needle will come to rest in the North South direction. 3 Measure the distance between these points on either side of the coil. ) 1 Perform this experiment by & - increasing the number of turns of the coil and see how far the magnetic 2 needle remains in the East West 0 Physics $ Standard - X direction on either side. Now the distance between the two points increases. Is it not due to the increase in the strength of the magnetic field? (It has to be ensured that the electric current is the same in both the experiments). Repeat the experiment changing the current using a rheostat. The strength of the magnetic field increases when the number of turns of the coil or current is increased. Record in the science diary the various factors affecting the magnetic effect of electricity. A solenoid is an insulated wire wound in the shape of a helix. Such coiled conductors are used to make use of the magnetic effect of electricity. Lets examine how we can recognise the direction of magnetic field and the polarity of a current carrying solenoid. Take an insulated copper wire of length not less than 1 m and make a solenoid (preferably a wire of gauge number 26) ) + , Count the number of turns in it. It will act as a magnet when current from a cell is passed through it after inserting a soft iron core. What is this device known as? With the help of a magnetic compass check the speciality of the magnetism at either ends of the solenoid. Current in the clockwise What is the change observed in the movement of the magnetic direction needle when the experiment is repeated after removing the ) + , soft iron core? From the movements of the magnetic needle in the magnetic compass, find out the polarity of the solenoid and mark them. Hold a current carrying solenoid with one end facing you. Note the direction of current at that end. Is it clockwise or anticlockwise? Find out the relationship between the direction of current and Current in the anti clockwise direction the polarity. ) +, The end of the solenoid at which current flows in the clockwise direction will be the South Pole and the end at which current flows in the anticlockwise direction will be the North Pole. Magnetic Effect of Electric Current ! $ 1 0 5 ! # $ ! * ! $ $ # switch " 3 $ A N B S Physics $ Standard - X 0 . " . " 0 0 # $ 1 . " 6 % / # $% &' ( ) ) ! / / $ " " Magnetic Effect of Electric Current + ( + ! 1 2 " # $1 $2 , ' # 1 " " 46 1 $ #!80 % % . ) ' 1 / : / / (- '). / % * * Physics $ Standard - X The electrical pulses from a microphone are strengthened using an amplifier and sent through the voice coil of a loudspeaker. The voice coil, which is placed in the magnetic field, moves to and fro rapidly, in accordance with the electrical pulses. These movements make the diaphragm vibrate, thereby reproducing sound. Now 8 6 Let us assess - 8 * + ) + , ) ) * ) 1 5 $ 5" & * ' #! * #! ) ) 8 & - #! * ) 5" / Magnetic Effect of Electric Current ; #! & - ! :" . 8/ * . 7 5 * % ) 1 < ) 1 ) 1 ) 1 9 = >1 5" % . ? 1 " / $ ! / + * 0 @ 1 08$ A # 0 Physics $ Standard - X -B * :. 1 $ Extended activities - $ " < & 8 08 $ 8 "/ ' 0 / " This machine How does supplies the it generate electricity required electricity? for all stages, Babu Can you clear Babus doubt? You know that electrical energy can be converted into many other forms. Write down some examples. You know that a solar cell converts solar energy into electrical energy. Like this which are the other forms of energy that can be converted into electrical energy ? Lets see whether we can convert magnetic energy into electrical energy. $ - X You have understood from the previous chapter that a conductor in a magnetic field experiences a force. As a result the conductor moves. If its so, will electricity be generated when a conductor is moved in a magnetic field? It was Michael Faraday who presented such an experiment for the first time. Lets do this experiment. Materials required Bar magnet Solenoid Galvanometer Arrange the above materials as shown in the figure. Insert the magnet into the solenoid and pull it out successively. Observe the deflection of the needle of the galvanometer each time. 3.1 (b) Record your observations in the table given below. Observation (Galvanometer needle) Sl. Experimental procedure Deflects/ Direction No. does not to the left/ deflect to the right ! " 46 Electromagnetic Induction Repeat the experiment using magnets of greater strength, and increasing the number of turns in the solenoid. On the basis of the experiment, complete the Table 3.2. Deflection of the galvanometer needle Experiment increases decreases # $ % & Galvanometer On the basis of the above experiment and analysis of the table, find out the answers to following questions ' and write them down in the science diary. ( Why did the galvanometer needle deflect in the ) experiment? & Which were the instances in which there was a flow of current through the solenoid? & Which were the instances in which the current increased? Electromagnetic Induction Whenever there is a relative motion between the magnet and the solenoid, there is flow of electricity. We have understood this from the experiment. But have you ever thought about what happens when the magnet is brought near or moved away from the solenoid? Observe the figure given below. (The figure indicates the two stages of doing the experiment) 47 Physics $ Standard - X On which instance will the magnetic flux linked with the solenoid be less? On which instance will the magnetic flux linked with the solenoid be greater? On which instance does a change in magnetic flux linked with the solenoid occur? (while it is moving/ while it is Michael Faraday stationary) Havent you understood that electricity is induced in a solenoid whenever there is a change in the KmÂht\m- a o- ä À kqNn magnetic flux linked with the solenoid? This FXnÀZn-ib - n hn{`w-in-¡p-¶p. phenomenon is known as electromagnetic induction. The current thus induced is the induced current. The voltage induced is the induced . (1791þ1867) What may be the factors affecting the induced emf? * + Number of turns of the coiled conductor , - + . / & + " + Whenever there is a change in the magnetic 0 flux linked with a coil, an emf is induced in 1 # the coil. This phenomenon is electro-magnetic .+ induction. / " & Which are the factors on which the direction of * / # # induced current in electromagnetic induction 2 * & depend? Direction of magnetic field (The direction of magnetic field is assumed to be from the North Pole to the South Pole.) The British Scientist John Ambrose Fleming discovered that the induced emf would be maximum if the conductor is moved perpendicular to the magnetic field lines. He also said that the relation between the direction of magnetic field, the direction of movement of the conductor and the direction of induced current could be explained in a simple way. This is known as Flemings Right Hand Rule 48 Electromagnetic Induction Fleming's right hand rule Imagine a conductor moving perpendicular to a magnetic field. Stretch the forefinger, middle finger and the thumb of the right hand in mutually perpendicular directions. If the fore finger represents the direction of the magnetic field, and the thumb represents the direction of motion of the conductor, then, the middle finger represents the direction of the induced current. Direction of motion of the Direction of conductor magnetic field Direction of current Lets see whether the current induced in a conductor from a magnetic field is the same as the current obtained from a battery/cell. Alternating Current ( AC), Direct Current (DC) A cell that can be used in a torch or a clock is connected in series with a resistor(6 kΩ) and a galvanometer. Note the direction of deflection of the needle of the galvanometer. Tabulate your observations. Then compare it with the observations in activity 2. &'''Ω G + - S $% # Activity Movement of Galvanometer needle Activity 1 ! Activity 2 " ! !! 49 Physics $ Standard - X The current obtained from the cell is unidirectional and is of the same magnitude. But what are the peculiarities of the current obtained by electromagnetic induction? Direction changes A current that flows only in one direction continuously is a direct current (DC). Current that changes direction at regular intervals of time, is an alternating current (AC). Is there any device that produces electricity continuously by the movement of a magnet or coiled conductor? It is such a device that you saw at the beginning of the chapter. Its name is generator. The cycle dynamo is also one such device. We use mechanical energy in generators to move the magnet or coiled conductor continuously. In that case what shall be the energy change in a generator? Mechanical energy → Generator is a device that converts mechanical energy into electrical energy by making use of electromagnetic induction. Generator The following figure will help you to understand the structure of a generator. Observe Fig 3.5(a) and write down the parts given in Fig. 3.5(b). Armature Field magnet Axis Slip rings Brush -Nn{Xw &. Slip rings Brush $ $ !" Electromagnetic Induction 02-3 Parts of AC generator 21, 22 Field magnet
