Physics - Electricity 2024 PDF

Physics - Electricity Overview: Static Electricity Electrical Energy Energy in Circuits Making Electrical Circuits Ohm’s Law Series and Parallel Circuits Ohmic vs Non-Ohmic Devices Modern Electronics 1. Static Electricity How do Atoms create a charge? How can a static...

Physics - Electricity Overview: Static Electricity Electrical Energy Energy in Circuits Making Electrical Circuits Ohm’s Law Series and Parallel Circuits Ohmic vs Non-Ohmic Devices Modern Electronics 1. Static Electricity How do Atoms create a charge? How can a static charge be made? What moves to cause a potential difference? Electricity occurs at the atomic level. Review: The Atom Matter is made up of atoms. + Proton (positively charged) sub-atomic particle – that cannot easily move. neutron (neutral): no charge. + + Neither positive or negative + – electron (negatively charged) sub-atomic particle – – that can move from one substance to another. atom nucleus Where do charges come from? Rubbing materials does NOT create electric charges. It just transfers electrons from one material to the other. Watch the Ted Ed Talk: The Science of Static Electricity - https://www.youtube.com/watch?v=yc2-363MIQs Discuss Where do charges come from? When a balloon rubs a piece of wool... Electrons are pulled from the wool to the – + balloon. – + – – + The balloon has more electrons than usual. – – + wool + The balloon: – charged, The wool: +charged  workbook pg 3 Static Electricity Static electricity: A build up of charge in an object that remains at rest Proton: Positively (+ve) charged sub-atomic particle that cannot easily move. Electron: Negatively (-ve) charged sub-atomic particle that can move from one substance to another. Neutral atom: No Charge. Neither positive or negative. Equal number of protons and electrons  workbook pg 3 When something is positively charged: Positive (+): Charge on a substance due to fewer electrons than protons. Negative (-): charge on a substance due to more electrons than protons. Atomic Structure Experiment 1: Static Electricity See logbook Aim: To Find Out a) How To Charge Objects and b) About The Effects Of Charges. Equipment Plastic charging rods, Glass charging rod, woolen and other cloths, tiny bits of paper or polystyrene, container of salt and pepper, paper plates. What to do 1. Rub the plastic rod vigorously with a woollen cloth. 2. Bring it near tiny bits of paper or polystyrene. Does it attract or repel them? 3. Test a charged rod by bringing it: a) near a single hair (or the hairs on your arm) b) near a thin smooth stream of water from the tap. c) near a container of salt and pepper. 4. Repeat steps 1 and 2 using different cloths. 5. Rub the glass rod vigorously with a cloth and check if you get the same results. 2. Electrical Energy 1. Circuits 2. Energy and current are different 3. Materials provide resistance to electric currents Circuits WHAT ARE THEY ALL ABOUT?  Video : How a circuit Watch the Twig video on Circuits works https://www.twig-world.com/ film/circuits-1555/ Discuss your findings Conductors and Insulators CONDUCTORS INSULATORS Materials which allow electrons to flow Materials which electrons cannot pass through. Examples: metals such as gold and iron. Examples: rubber, wood, plastic, glass Challenge: Making the right connections Use the PHET simulation https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-kit-dc_all.html Make the following circuit Once the globe in the circuit lights up swap the settings from pictures to circuit symbols Challenge: Making the right connections Copy these symbols into your workbook 2 That are not connected  See logbook Experiment 3: Conductors vs insulators Conductors – allow electricity to flow Insulators – stop electricity from flowing ✓Set up circuit like I have in pHet ✓Test each material and complete the table ✓Answer the questions (in full sentences and with detail!) 3. Energy in Circuits 1. Voltage is a measure of potential difference 2. Current is the rate of movement of electrons 3. Resistance opposes voltage Electric Circuit Basics All electrical circuits consist of 3 things to make them work: 1. A power supply to provide the electrical energy. 2. A load (or loads) in which electrical energy is converted into other useful forms of energy. e.g. a light globe. (Loads provide resistance to current flow and energy is used up to overcome this resistance.) 3. A conducting path that allows electric charge to flow around the circuit.  Power Supply Batteries store chemical energy in the substances inside them. This chemical energy is transformed into electrical energy when a chemical reaction takes place inside the cell. The electrical energy you use from a powerpoint comes from a power station, which is different to a battery. Current & Voltage Electric current is the flow of electrical charge, just like you learnt with static electricity. Current is the measure of the amount of electric charge passing a particular point in an electric circuit every second. The current is caused by the flow of electric charge (electrons in metals), however, electric current is defined as the direction of the movement of positive charge. Electric current is said to flow through a circuit from the positive terminal to the negative terminal of the power supply. Conventional Current vs Electron Flow Electricity was first discovered in 1752 by Benjamin Franklin by flying a kite in a thunderstorm. He decided that electricity was the flow of charge from positive to negative. It wasn’t until 1897 that J. J. Thompson discovered the electron and as a consequence scientists realised they had got electric charge wrong! In metals it was the negatively charged electrons flowing causing a current not positively charged particles. In a solution of salts where both positive and negative charges are free to move then conventional current is the directions the positive charges move and electron flow is in the opposite direction. Since it had been established for over 100 years that current represented the flow from positive to negative the decision was made to not change the rules so if we talk about what electrons do we use the term electron flow, which is always opposite to conventional current. What is electricity? Video: Watch the Twig Video: ‘What is Electricity?’ https://www.twig-world.com/film/what-is-electricity-1540/ Write down 3 things you learnt. Current, Voltage & Charges in Circuits Current is a measure of how quickly the Voltage is a measure of how much energy each charges move. Just as a water current in charge has. a river. The voltage is the amount of fuel the car has. A petrol station is like a battery in a circuit as it An analogy is consider a car as a charge. adds (energy) to the car. The current is the speed the car is travelling. NOTE: the car itself is not used up just like charges in a circuit are not used up. Voltage is the amount of energy possessed by a fixed quantity of electric charge (called a Coulomb). As the charges move through the circuit they lose voltage as it is converted to other energy forms such as heat, light, sound or kinetic, this loss is called voltage drop (often also incorrectly called voltage). Another name for voltage drop is potential difference as it measures a change in potential (stored) energy of charge as it moves between one place and another. As electric charge moves through a circuit it gains electrical energy from the power supply and loses the same amount of energy as it passes through the circuit. i.e. the voltage gain across the terminals of the power supply is equal to the total voltage drop across the rest of the circuit.  Load This is the energy converter in the circuit. This is where most of the electrical energy carried by the charge is transformed into useful forms of energy such as light, heat and sound. Every Load provides resistance to the flow of the charges. 4. Resistance Is any opposition to the flow of charge through a circuit is measured using the units ohm (Ω) and is represented by the letter R. Video: https://www.youtube.com/watch?v=8jB6hDUqN0Y Conducting path Pathway which allows the flow of electricity Usually made of metals such as copper, which have little resistance Low resistance means that the electricity flows freely and energy is not lost due to friction (heating of the pathway). Resistance how hard it is for the current to pass through higher resistance means more energy needed for current to flow through a resistor is any component that restricts the flow of electrons unit: Ohms (Ω) symbol: R a multimeter (connected in parallel) can be used to measure the resistance of a device (load). Example: 1st Band: Green = 5 2nd Band: Blue = 6 3rd Band: Multiplier = Orange = 1000 Value: 56 x 1000 = 56,000 Ohms  1st Band: Brown = 1 1st Band: Brown = 1 2nd Band: Black = 0 2nd Band: Black = 0 3rd Band: Multiplier = Red = 100 Your turn: 3rd Band: Multiplier = Brown = 10 Value: 10 x 10 = 100 Ohms Value: 10 x 100 = 1,000 Ohms 1st Band: Brown = 1 1st Band: Brown = 1 2nd Band: Black = 0 2nd Band: Black = 0 3rd Band: Multiplier = Blue = 1,000,000 3rd Band: Green = 5 Value: 10 x 1,000,000 = 10,000,000Ohms 4th Band: Multiplier = Brown = 10 Value: 105 x 10 = 1,050 Ohms 5. Making Electric Circuits 1. Electricity will only flow through a complete circuit 2. Electrical circuits can be planned and drawn using diagrams 3. Circuit components are shown using standard symbols  Electric circuits SERIES PARALLEL Series and parallel circuits https://www.youtube.com/watch?v=x2EuY qj_0Uk  Electric circuits SERIES In this type of circuit all components are connected one after the other. This means there is only one loop for the electric current to flow through. An example is the torch we looked at before. The circuit must be complete in order for the electrons to flow and create an electric current. Series Circuit Characteristics In a series circuit the electrical energy is shared amongst each globe. As you add more globes the brightness of each will dim. The current flowing in a series circuit does not change as there is only one path for the electrons to flow. So the current at the beginning of the circuit will be the same in the middle and at the end. If one globe was to burn out then this would create a break in the circuit and hence no other globes would work as the circuit is then not complete. Example Consider the following circuit containing identical lamps A, B and C in series. (a). Describe the brightness of the three lamps. Each will have the same brightness however they will be dim. (b) Compare the currents that flow through lamp A and lamp C. The brightness of A and C will be the same (c). If the filament in bulb B burns out, will any of the lights remain lit? Explain. If B goes out the whole circuit will not work as this provides a hole in the circuit. PARALLEL In a parallel circuit, there is more than one resistor (bulb) and they are arranged on many paths. This means electricity (electrons) can travel from one end of the battery through different branches to the other end of the battery. From the above, it is clear that electricity from the battery can take either path A or Path B to return to the battery. The great thing about parallel circuits is that, even when one resistor (bulb) burns out, the other bulbs will work because the electricity is not flowing through one path. Think of all the light bulbs in your home. If one bulb burns out, the other bulbs in the rooms still work. Another great thing is that the bulbs in a parallel circuit do not dim out like the case in series circuits. This is because the voltage across one branch is the same as the voltage across all other branches. Example: Consider the following circuit containing identical lamps A, B and C parallel. These lamps are the same as those for Circuit in the series example previously. (a). Describe the brightness of the three lamps. Each globe will glow brightly with the same intensity (b) Compare the currents that flow through lamp A and lamp C. The currents through A and C are the same. (c). Compare the brightness of the lamps in this circuit to their brightness in the series circuit. Explain any differences. The brightness in the lamps for the parallel circuit is more intense than the series circuit as the supply voltage is not shared amongst the globes like in the series circuit. A switch Scenario Question L2 and L3 L2 and L1 no globes will work Short Circuits: When there is a path within a circuit which has no resistance (or very little) the current will take this path. This is known as a short circuit. Often a short circuit can lead to a device becoming hot or catching on fire. The other components in the circuit will therefore not operate. Example Draw on the circuit below which path the current will take when the switch is open and when the switch is closed?  PHET simulator Voltage, current and Videos resistance https://www.youtube.com /watch?v=J4Vq-xHqUo8 Re-cap Current = flow of charges (electrons) through a circuit We use an ammeter, set up in series, to measure the current in amps or milliamps Voltage = amount of energy that the charges (electrons) have at a given point. A difference in voltages at different parts of a circuit is called a voltage drop or a potential difference (change in stored energy between two points in the circuit). We use a voltmeter, set up in parallel, to measure the volts. 6. Series and Parallel Circuits 1. In series circuits, components are connected one after another 2. In parallel circuits, components are on different branches  Series circuits Comparing the voltage and current in series circuits. – PHET simulator ✓As more loads are added to the circuit, there is a decrease in current. ✓Light globes become more dim as you increase the number of loads within the circuit. ✓The current is the same throughout each load within the circuit. ✓Sum of the voltage drops across each load = voltage (potential) of the power supply.  Parallel circuits Comparing the voltage and current in parallel circuits – PHET simulator ✓Two loads/globes added in parallel = increase in current. ✓Both lights glow brightly. ✓The sum of the current flowing through each branch = overall current of the circuit. ✓Voltage is consistent across each load.  1. Draw circuits for the following: ✓ One 6V battery, two light globes in series, one switch between the battery and the first light globe, a voltmeter measuring the potential difference across the first light globe. ✓ One 6V battery, two light globes in parallel, one switch that controls the whole circuit, one ammeter measuring the current from the battery, one voltmeter measuring the potential difference across one light globe. Tasks ✓ One 6V battery, two light globes in series, one in parallel, one switch that controls the globes in series only, an ammeter measuring the current across the globe that’s in parallel. ✓ For the above: Comment on the brightness of the lamps, the current and voltage flowing through each lamp. Terminology Electricity: flow of charge Electric current: flow of moving charges, from positive to negative terminals Electron Flow: electrons flowing from negative to positive) Voltage: amount of energy charges have at a given point Current: rate of flow of charges (in wires; electrons) Using Ammeters and Voltmeters Khan Academy AMMETERS VOLTMETER video ➔ A device that measures the size of the ➔ A device that measures the voltage (energy electric current flowing in a circuit between two points in a circuit) ➔ Unit: amps (A) or milliamps (mA) ➔ The unit for voltage is: volts (V) ➔ Ammeters must be connected in series ➔ Voltmeters must be connected across a source or ➔ Positive (red) closer to positive of power load i.e. in parallel supply. ➔ a voltmeter or multimeter in parallel measures voltage ➔ Connect positive (red) terminal of voltmeter or multimeter to red terminal of battery Always start on the highest value. If your reading is too low, then move to the smaller one. Remember to read the scale according to the positive terminal you’re connected to.  workbook pg 24 Measurements in electric circuits Ammeter ◦ A device that measures current. ◦ Unit: Amperes (A) or Amps, we also use milliamperes (mA), meaning smaller current because currents are often very small. ◦ The symbol for an ammeter is: Measurements in electric circuits Ammeter: ◦ Ammeters must be connected in series, i.e. in the path of the circuit. ◦ Connect positive (red) terminal of the ammeter to the positive terminal of battery ◦ Use the positive terminal with the highest value first ◦ Use the scale which matches the connected positive terminal ◦ Always read the ammeter from directly in front, not side on. Ammeter The positive terminal of the ammeter is closest to the positive terminal of the power supply Connected in series Measurements in electric circuits Voltmeter ◦ Used to measure: ◦ the voltage gain across the terminals of a power supply. ◦ the voltage drop across parts of an electric circuit ◦ Measured in volts (V) ◦ The symbol for a voltmeter is:  Measurements in electric circuits Voltmeter: ◦ Voltmeters must be connected across a source or load i.e. in parallel. ◦ a voltmeter or multimeter in parallel measures voltage ◦ connect positive (red) terminal of voltmeter or multimeter to positive terminal of battery. Errors in measurement When reading scales errors can occur because often an estimation is being made. This voltmeter can be read as 2.3 V. Due to the thickness of the needle it could be 2.29 V or 2.31 V.  Errors in measurement Random errors: Caused due to estimation When the quantity being measured changes randomly and quickly: temperature of water in a saucepan. Systematic errors: Due to incorrect use or limitations of equipment ie scale not on zero when not connected to the circuit Results may be consistently low or high. Errors in measurement Reducing errors: Random errors can be reduced by repeating measurements several times and finding an average. Some systematic errors can be eliminated by using the equipment correctly. If an instrument doesn’t give a ‘zero’ reading when it should, the amount it is ‘off’ can be added or subtracted from the result. Investigation- Series & Parallel Circuits ✓Use PhET simulation https://phet.colorado.edu/sims/html/ circuit-construction-kit-dc/latest/circui t-construction-kit-dc_all.html ✓Read method ✓Construct circuits ✓Draw a diagram of each circuit ✓Record results and answer questions as you go. 7. Ohm’s Law 1. Electrical current is proportional to voltage 2. Voltmeters measure potential difference 3. Ammeters measure current Ohmic Conductors  page 35 of booklet Ohmic conductors Current( A) Voltage (V) 2 4 4 8 6 12 8 16 10 20 Examples 1. For the circuit shown below, the voltage across the battery is 6V and the current flowing through the globe is 2 A. Find the resistance of the globe R = V/I R=6/2 R = 3 Ohms Examples Examples 3. If the voltage across a resistance is doubled, what will happen to the current? Answer: The current will double as well. Explanation: If you look at the equation V= IR, if R stays the same then if you multiply voltage by 2 (double the voltage), you must also double the current for the equation to remain true. Examples 4. A resistor of 3Ω is connected to a 9V battery. What is the current flowing through the resistor? I = V/R I=9/3 I=3A Examples 5. A current of 10A flows through a conductor of 4 Ω. What voltage drop occurs over the conductor and therefore what is the size of the battery? V = IR V = 10 x 4 V = 40 Volts 8. Ohmic vs Non-ohmic Devices Ohmic devices obey Ohm’s Law V = RI and have linear V-I graphs Ohmic devices have a constant resistance Non-ohmic devices have a varying resistance and don’t obey Ohm’s Law Non-ohmic conductors Non-ohmic conductors do not follow Ohm’s law. When graphing Voltage v Current, the graph is non-linear E.g: LEDs, globes  page 35 of booklet Non-ohmic conductors Current(A) Voltage (V) 1 1 2 4 3 9 4 16 5 25 9. Modern Electronics 1. Advances in digital circuits opened up many possibilities in electronics 2. Graphene to make small 2D circuits 3. Electronic sensors have many applications Graphene