1. Electricity 2 Thomas Edison 1847-1931

2. Lesson Objectives I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

3. Task: Draw some circuit symbols for common components found in an electrical circuit. Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

4. Cell – push electrons around the circuit Battery – consists of 2 or more cells Switch – enables current to be switched on or off Lamp – emits light Ammeter – measures current. A Voltmeter – measures voltage V Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. The ones you should know already

5. Other Components and their symbols: Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. Diode – only allows current in ONE DIRECTION ONLY. Fixed resistor – limits current flowing in a circuit Variable resistor – varies current flowing in a circuit

6. Other Components and their symbols: Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. Fuse – a wire that melt when current is TOO high. Heater – converts electrical energy into thermal.

7. Circuit 1Circuit 2Circuit 3 1 cell, 1 bulb 1 cell, 2 bulbs1 cell, 3 bulbs A1A1 A1A1 A1A1 A2A2 A2A2 A2A2 Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. Conclusion – current is the same in all places in a SERIES circuit.

8. N N = normal brightness B = bright D = dim Circuit 1 Circuit 2Circuit 3 Circuit 5Circuit 4Circuit 6 1 cell 1 bulb 2 cells 2 bulbs 3 cells 3 bulbs 3 cells 1 bulb1 cell 2 bulbs2 cells 1 bulb NN NN N BBDD Conclusion – voltage is the shared between components in a SERIES circuit. Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

9. Voltage in a series circuit The battery provides energy to the circuit. The energy in the battery is stored as chemical energy and is transformed into electrical energy. This energy is carried by the electrons around the circuit. Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

10. Potential Difference (PD) Potential Difference (PD) is a measure of the energy flowing through a part of the circuit and is measured in Volts (V) using a voltmeter Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

11. Potential Difference (PD) in a series circuit. A voltmeter is places in parallel to measure the Potential Difference (PD) across a component. Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

12. ?V 3V Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

13. 3V 1.5V All of the bulbs are now dimmer as the Potential Difference (PD) is shared between the two bulbs Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

14. 3V 1V All of the bulbs are now dimmer as the Potential Difference (PD) is shared between the three bulbs Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

15. Conclusion: Current is the same at all points in a series circuit. Potential Difference (PD) is shared between the components in a series circuit. Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

16. Resistance: When electrons pass through a component, they will experience a different amount of resistance. This is caused by the vibrating atoms getting in the way of the electrons trying to get through. Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

17. Resistance: This is measured by: Potential difference (volts) = Resistance (Ohms) Current (amps) Short hand: R = V I Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. The current through a wire is 2.0A when the potential difference across it is 12V. Calculate the resistance of the wire. 12/2 = 6 Ohms (  )

18. Resistance: When current passes through a wire it gets hot. These are results from a set of students who investigated if resistance changes when current is changed. Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. Current (A)0.050.100.150.200.25 Potential difference (V) 0.501.001.502.002.50 Draw a graph of results and write a conclusion.

19. Conclusion: Current is directly proportional to potential difference in this wire. Therefore, resistance remains constant. This is known as Ohm’s law – “The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor”. (Known as an Ohmic conductor). Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.

20. A filament lamp Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. Curve – therefore not directly proportional, so not an ohmic resistor. Resistance increases as current increases Caused by increase in temperature as current increases. Reversing the current has not effect – they are a mirror image.

21. Diode Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. Only works in ONE direction No a straight line – so not an ohmic conductor. Reverse direction, the current is negliable.

22. Thermistor Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. High Temp Low Temp Current Potential Difference Straight line – therefore directly proportional, so an ohmic resistor at constant temperature. Resistance decreases as temperature increases

23. Light dependent resistor (LDR) Keywords: I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law. High Light Dim light Current Potential Difference Straight line – therefore directly proportional, so an ohmic resistor at constant temperature. Resistance decreases as light increases

24. Are you now able to…. I still feel unsure. I need some more help to understand. I feel ok. I need to do some more work to check my understanding. I am happy and feel I understand and can explain the main points. I know some circuit symbols for common components. I know what is meant by resistance I know what is Ohm’s law.