Measuring current

1. Measuring current A A The unit of measure forcurrentis the amp, which has the symbol A. Current is measured using a device called anammeter. In a circuit diagram, an ammeter is shown by the symbol . A When measuring the current through a component, the ammeter is always connected inseries(in the same loop) with that component.

2. Experiment 1: Current in series circuit A A R1 Circuit 1 1 2 1. Set up the circuit as shown above. 2. Measure the current using the ammeter at positions 1 and 2.

3. Experiment 1: Current in a series circuit A A R1 Circuit 2 1 3 A R2 2 1. Add another resistor into the circuit (R2) and another ammeter after it. 2. Now measure the current using the ammeter at positions 1, 2 and 3.

4. Experiment 1: Current in a series circuit – results A A A A A R2 R1 R1 Circuit 1 Circuit 2 1 3 1 2 2 Circuit 1 results: Current at position 1 = Current at position 2 = Circuit 2 results: Current at position 1 = Current at position 2 = Current at position 3 =

5. Experiment1:Current in a series circuit–summary A A A A A R2 R1 R1 Circuit 1 Circuit 2 Circuit 1 The current at different positions in the circuit, before and after the resistor, was the _______. Current is _____ used up by the components in the circuit. Circuit 2 Increasing the number of components in the circuit ________ the current. The current at all points in a series circuit is the _______. same / same / decreased / not

6. What is a parallel circuit? B A A parallelcircuit is one which contains a point (a junction) where the current cansplit(point A) orjoin(point B). This means that there is more than one path around the circuit.

7. Measuring current in a parallel circuit A4 A1 A2 A3 1. Place the ammeter, in turn, at positions 1, 2, 3 and 4. 2. Record the ammeter readings in the table.

8. Current in a parallel circuit A4 A1 A2 A3 In a parallel circuit, the current that leaves the cell is the same as the current that returns to the cell. A1 = A4 The current does not get used up by the circuit, just the energy that the electrons are carrying.

9. Current in a parallel circuit A4 A1 A2 A3 The current splits up at the first junction and then joins together at the second junction. The following is always true for this type of parallel circuit: A1 = (A2 + A3) = A4 If the bulbs are identical then the current will split evenly. If the bulbs are not identical, then the current will not split evenly.

10. Contents 9I Energy and Electricity Generating electricity Measuring current Measuring voltage Energy in circuits Summary activities

11. Measuring voltage Voltageis measured using a device called a voltmeter. In a circuit diagram, a voltmeter is given the symbol . V V1 V2 V3 Voltageis the amount of push and is measured in ‘volts’, which has the symbol V. When measuring the voltage across a component, the voltmeter is always connected inparallelwith (or across) the component. This is still a series circuit. The voltage supplied by the battery is shared between all the components in a series circuit.

12. Experiment 2: Voltage in a series circuit V R1 V Circuit 1 1. Set up the circuit as shown above. 2. Connect the voltmeter across the power supply (battery) and measure the supply voltage. 3. Then connect the voltmeter across the resistor (R1) and measure this voltage.

13. Experiment 2: Voltage in a series circuit V R1 V1 V2 Circuit 2 R2 1. Add another resistor (R2) to the circuit as shown. 2. Connect the voltmeter across the power supply (battery) and measure the supply voltage. 3. Then measure the voltage across each of the resistors.

14. Experiment 2: Voltage in a series circuit – results Circuit 1 Circuit 2 V V R1 R2 R1 V V1 V2 Circuit 2 results: Voltage (supply) = Voltage (R1) = Voltage (R2) = Circuit 1 results: Voltage (supply) = Voltage (R1) =

15. Experiment 2:Voltage in a series circuit–summary Circuit 1 Circuit 2 V V R R2 R1 V V1 V2 The current is the _______ of electricity around the circuit. The _________ is the amount of push. When two components were put into Circuit 2, the voltage of the supply was the _______ as Circuit 1. However, the voltage across R1 __________ . The voltage across both components in Circuit 2 added to be equal to the ________ voltage. supply / decreased / voltage / flow / same

16. Measuring voltage in a parallel circuit V1 V2 V3 Connect up this circuit and measure, in turn, the voltage at V1, V2 and V3. Record your results in the table. What do you notice about the results? How can you explain this?

17. Experiment 3: Cells in a series circuit V A R V Circuit 1 1. Set up the circuit as shown above. 2. Connect the voltmeter across the power supply (battery) and measure the supply voltage. Then measure the voltage across the resistance. Also measure the current.

18. Experiment 3: Cells in a series circuit V A R V Circuit 2 1. Add an additional battery to the circuit. 2. Connect the voltmeter across the power supply and measure the supply voltage. Then measure the voltage across the resistance. Also measure the current.

19. Experiment 3: Cells in a series circuit – results V V A A R R V V Circuit 1 Circuit 2 Circuit 1 results: Voltage (supply) = Voltage (R) = Current = Circuit 2 results: Voltage (supply) = Voltage (R) = Current =

20. Experiment 3: Cells in a series circuit – summary V V A A R R V V Circuit 1 Circuit 2 Delete the wrong answer: Increasing the number of cells increases/decreases the current that flows in the circuit. The current/voltage depends on the current/voltage.

21. Current and voltage – key ideas • Current • In a series circuit, the current is the same in all parts of the circuit. • In a parallel circuit, the current splits up and recombines when the branches of the circuit meet up. (The sum of the current in the branches equals the total current.) • The current depends on the voltage in any circuit. • Voltage • In a series circuit, the supply voltage issharedbetween the components. (The sum of the voltage across each component is the same as the total supply voltage.) • In a parallel circuit, the voltage across each component is the same as the supply voltage.

22. Contents 9I Energy and Electricity Generating electricity Measuring current Measuring voltage Energy in circuits Summary activities

23. Energy transfer in circuits Energy cannot be created or destroyed. In all devices and machines, including electric circuits, energy is transferred from one type to another. When this circuit is connected, chemical energy stored in the battery is transferred via electrical energy to heat and light energy in the bulbs. The total amount of heat and light energy is the same as the amount of chemical energy lost from the battery.

24. Energy transfer in electrical circuits 5J transferred to bulb as light energy 95J transferred to chemical energy from battery (e.g. 100J) heat energy of bulb Most of the energy from the battery does not produce light – most of it is wasted as heat!

25. Calculating energy efficiency useful energy output %Efficiency = x 100 total energy input ( ) Efficiency of bulb = 10 200 = 5% x 100 The efficiency of an energy transfer can be calculated using this formula: This bulb converts 200J of chemical energy form battery into 10J of useful light energy:

26. What’s the energy transfer? Batteries can power many electrical devices. What sort of energy is electrical energy transferred into in these electrical devices?

27. Glossary • current –The flow of electricity, measured in amps (A). • efficiency –A measure of how much energy is changed from one type of energy to another. • potential difference –The amount of ‘push’ or electrical energy there is in a circuit, measured in volts (V). • power –The amount of energy that an electrical device uses per second, measured in watts (W). • power station –A place where an energy resource is transformed into electrical energy. • transfer –To move energy from one place to another. • transform –To change energy from one type to another. • voltage –Another name for ‘potential difference’.