1. Potential difference ( Potential difference ( Spannungsdifferenz) Spannungsdifferenz

2. Objectives Explain potential difference using a water analogy Describe how to measure potential difference Calculate potential difference in different parts of a circuit

3. Thinking time… How could you get more water to flow from a hosepipe? ◦

4. More thinking… How could you get more water to flow from a hosepipe? ◦ open the tap more How does this link to electricity?

5. Potential difference ( Potential difference (Spannungsdifferenz)Spannungsdifferenz Potential difference is the difference in electrical “pressure” between 2 points If there is a difference, electrons will flow from the more negative point if there is a conductor A very high potential difference forces more current through a circuit Also known as Voltage Units = Volts (V) Symbol = U

6. Measuring potential difference Use a voltmeter in parallel Eg. measuring the difference in potential across a bulb

7. Experiment Set up the circuit as shown Set the power supply to 6V Measure the voltage at the places indicated What rule can you create? LocationU / V V1V1 V2V2 V3V3 V4V4

8. Measuring voltage in different parts of a circuit In a series circuit, the sum of the potential differences across each device is equal to the potential difference across the power supply V 1= V 2 +V 3 +V 4 LocationU / V V1V1 V2V2 V3V3 V4V4

9. Typical voltages ItemTypical voltage Nerve cell75mV AA cell1.5V Rechargeable AA cell1.2V Car battery12V Mains power230V High speed train power lines25kV High voltage power lines110kV Lightning10MV

10. Voltage drop You have been the difference in voltage across bulbs What causes this? What would an analogy be with water?

11. Workers playing with high voltage power lines Workers playing with high voltage power lines