Current, Charge and Power

Transcription

1 Current, Charge and Power Match up the electrical quan66es, with their abbrevia6ons and units. I V E power ampere Ω Energy Ohms Voltage volts resistance waas joule P current Can you provide any defini6ons for these units? Extension: can you describe how these factors are interrelated by giving equa6ons 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 poten6al difference C Find the fuse required for an appliance based on its electrical power ra6ng B Perform calcula6ons involving rearrangement of the electrical power equa6on A Perform calcula/ons involving rearrangement of the Energy transferred, poten/al difference and charge equa/on: 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 s6ll 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 hea6ng 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 ra/ng of an appliance is given on the back of the appliance. Power ra6ng is the rate at which an appliance transfers energy. It is measured in joules per second, called waas. One waa is one joule per second (1W= 1J/s) P = E/t where P is Power in waas (W) E is energy in joules (J) T is 6me in seconds (s)

6 Energy and Power A portable fan transfers 1800 joules of energy in 60 seconds. What is its power ra6ng? 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 Calculate the power of an electrical appliance from the current and the poten6al difference C 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)

9 Calculate the power of an electrical appliance from the current and the poten6al difference C 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 I P V and you are left with the sum I = P V x

10 Calculate the power of an electrical appliance from the current and the poten6al difference C 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 Calculate the power of an electrical appliance from the current and the poten6al difference C 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 200V P = 40W

12 Calculate the power of an electrical appliance from the current and the poten6al difference C Perform calcula6ons involving rearrangement of the electrical power equa6on A 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

13 Calculate the power of an electrical appliance from the current and the poten6al difference C Perform calcula6ons involving rearrangement of the electrical power equa6on A 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? 600 W

15 kv, kj, kw 1 kv = 1000 V 1 kj = 1000 J 1 kw = 1000 W How many kilovolts in 9 000V? 9.0 kv How many kilojoules in J? 23.5 kj How many kilowatts in 325W? kw

16 Find the fuse required for an appliance based on its electrical power ra6ng B Power and Fuses The table shows the power ra6ngs of different electrical appliances. A Calculate the current used by each appliance. (Hint: don t forget to change kw to W before calcula6ng 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. Appliance Power rating Current (A) Fuse a Computer b Fridge c Fridge-freezer d Lawnmower e Toaster f TV g Hair dryer h Electric fire (2 bars) i Tumble dryer j Kettle 67 W 63 W 100 W 900 W 850 W 90 W 1 kw 2 kw 1.5 kw 2.5 kw

17 Find the fuse required for an appliance based on its electrical power ra6ng B Power and Fuses The table shows the power ra6ngs of different electrical appliances. A Calculate the current used by each appliance. (Hint: don t forget to change kw to W before calcula6ng 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. Appliance Power rating Current (A) Fuse a Computer 67 W A b Fridge 63 W A c Fridge-freezer 100 W A d Lawnmower 900 W A e Toaster 850 W A f TV 90 W A g Hair dryer 1 kw A h Electric fire (2 2 kw A bars) i Tumble dryer 1.5 kw A j Kettle 2.5 kw A

18 Perform calcula/ons involving rearrangement of the Energy transferred, poten/al difference and charge equa/on: E = V x Q A/A* (HT only) The energy transferred to a unit of charge by a baaery 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: A charge of 50C moves through a poten6al difference of 12V. How much energy is transferred to the charge? E= V x Q = 12V x 50C = 600J E= V X Q Where E is energy transferred in joules (J) V is the poten6al difference in Volts (V) Q is the charge in coulombs (C)

19 Perform calcula/ons involving rearrangement of the Energy transferred, poten/al difference and charge equa/on: E = V x Q A/A* (HT only) The poten6al 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 poten6al difference C Find the fuse required for an appliance based on its electrical power ra6ng B Perform calcula6ons involving rearrangement of the electrical power equa6on A Perform calcula/ons involving rearrangement of the Energy transferred, poten/al difference and charge equa/on: E = V x Q A/A* (HT only)