1. Current, Charge and Power Match up the electrical quantities, with their abbreviations and units. IVE powerampereΩ EnergyOhmsVoltage voltsresistancewatts joulePcurrent Can you provide any definitions for these units? Extension: can you describe how these factors are interrelated by giving equations or describing the links in sentences?

2. Current, Charge and Power State what the power of an appliance is –D Calculate the power of an electrical appliance from the current and the potential difference –C Find the fuse required for an appliance based on its electrical power rating –B Perform calculations involving rearrangement of the electrical power equation –A Perform calculations involving rearrangement of the Energy transferred, potential difference and charge equation: E = V x Q –A/A* (HT only)

3. Power State what the power of an appliance is –D

4. Power The popular name for Compact Fluorescent Lamps (CFLs) is still “energy saving bulbs”. What does this mean? Filament lamps become hot when they are switched on, CFLs do not Energy is transferred to a filament lamp by the current flowing through it. Most of this energy is transferred away from the bulb by heating the surroundings. The CFL is much more efficient. It transfers most of the energy to give light, not heat. The CFL “uses” less energy to produce the same amount of light.

5. Energy and Power The power rating of an appliance is given on the back of the appliance. Power rating is the rate at which an appliance transfers energy. It is measured in joules per second, called watts. One watt is one joule per second (1W= 1J/s) P = E/t where P is Power in watts (W) E is energy in joules (J) T is time in seconds (s)

6. Energy and Power A portable fan transfers 1800 joules of energy in 60 seconds. What is its power rating? P=E/t = 1800J/60s = 30W A mains-powered hairdryer is rated at 500W. How much energy will it transfer in 1 minute? E=Pxt = 500 x60 = 30,000J

7. Demo I have plugged in a 40W, 60W and 100W lamp. What can you see? What does this relate to?

8. We can express the relationship between current, voltage and power mathematically using the equation: Power = Current x Voltage P=IV Voltage measured in Volts (V) Current measured in Amps (A) Power measured in Watts (W) Calculate the power of an electrical appliance from the current and the potential difference –C

9. P I VV  x As always formula triangles help you to rearrange formula, the triangle for the Power Law is shown below: Whatever quantity you are trying to find cover it up and it will leave you with the calculation required. So if you were trying to find current, I….. …you would cover I up… …and you are left with the sum… I = P V Calculate the power of an electrical appliance from the current and the potential difference –C

10. For the 40W, 60W and 100W bulbs calculate the current flowing. 0.17A, 0.26A and 0.43A What fuse should each of the lamps have?

11. If you have a filament bulb and it has a potential difference of 200V across it and a current of 0.2A running through it. At what power is the bulb operating at? P = IV P= 0.2A x 200 V P= 40W Calculate the power of an electrical appliance from the current and the potential difference –C

12. If you have a filament bulb and it operates at a power of 60W and it has a potential difference of 240V across it, what is the current running through the bulb? P = IV I= P/V I= 60W / 240V I= 0.25A Calculate the power of an electrical appliance from the current and the potential difference –C Perform calculations involving rearrangement of the electrical power equation –A

13. Questions: Calculate the power supplied to a 5A, 230V electric heater. Calculate the power supplied to a 13A, 230V television. Calculate the power supplied to a 3A, 230V kettle. Calculate the current going into a 60W bulb with 230V going through it.

14. kV, kJ, kW 1 kV = 1000 V 1 kJ = 1000 J 1 kW = 1000 W How many Volts in 6kV?_________ V How many Joules in 12.3kJ?_________ J How many Watts in 0.6kW?_________ W 6 000 12 300 600

15. 1 kV = 1000 V 1 kJ = 1000 J 1 kW = 1000 W How many kiloVolts in 9 000V?_________ kV How many kiloJoules in 23 500J?_________ kJ How many kiloWatts in 325W?_________ kW 9.0 23.5 0.325 kV, kJ, kW

16. Find the fuse required for an appliance based on its electrical power rating –B Power and Fuses AppliancePower ratingCurrent (A)Fuse aComputer67 W bFridge63 W cFridge-freezer100 W dLawnmower900 W eToaster850 W fTV90 W gHair dryer1 kW hElectric fire (2 bars) 2 kW iTumble dryer1.5 kW jKettle2.5 kW The table shows the power ratings of different electrical appliances. A Calculate the current used by each appliance. (Hint: don’t forget to change kW to W before calculating your answer.) B Work out what size fuse would be needed by the plug for each appliance. Choose from: 3 A, 5 A, 13 A.

17. Find the fuse required for an appliance based on its electrical power rating –B Power and Fuses AppliancePower ratingCurrent (A)Fuse aComputer67 W 0.293A bFridge63 W 0.273A cFridge-freezer100 W 0.433A dLawnmower900 W 3.915A eToaster850 W 3.705A fTV90 W 0.403A gHair dryer1 kW 4.345A hElectric fire (2 bars) 2 kW 8.7013A iTumble dryer1.5 kW 6.5213A jKettle2.5 kW 10.8713A The table shows the power ratings of different electrical appliances. A Calculate the current used by each appliance. (Hint: don’t forget to change kW to W before calculating your answer.) B Work out what size fuse would be needed by the plug for each appliance. Choose from: 3 A, 5 A, 13 A.

18. A charge of 50C moves through a potential difference of 12V. How much energy is transferred to the charge? E= V x Q = 12V x 50C = 600J Perform calculations involving rearrangement of the Energy transferred, potential difference and charge equation: E = V x Q –A/A* (HT only) The energy transferred to a unit of charge by a battery or power supply is the same as the work done on the unit of charge. Replacing W (work done) with E (energy transferred) in V=W/Q And then rearranging, gives: E= V X Q Where E is energy transferred in joules (J) V is the potential difference in Volts (V) Q is the charge in coulombs (C)

19. Perform calculations involving rearrangement of the Energy transferred, potential difference and charge equation: E = V x Q –A/A* (HT only) The potential difference across a bulb is 5V and the current through the bulb is 3A. In one minute, how much energy will be transferred by charge passing through the bulb? Q= I x t = 3A x 60s = 180C E = V x Q = 5V x 180C = 900J

20. Electrical error “I’m sick of all my stuff fusing; I’m going to put a 13A fuse in all of my things so that they’ll keep working” Is this a good plan or not? Discuss and write down the hazards associated with doing this. State what the power of an appliance is –D Calculate the power of an electrical appliance from the current and the potential difference –C Find the fuse required for an appliance based on its electrical power rating – B Perform calculations involving rearrangement of the electrical power equation –A Perform calculations involving rearrangement of the Energy transferred, potential difference and charge equation: E = V x Q –A/A* (HT only)