1. What comes to mind when you think of POWER

2. Power
16/07/2018
LO:
Derive our simple electrical power formulae and practice until proficient
Predict and calculate how much electricity costs

3. Define current –
Define Potential difference –
Define Power -
Can you link the three?

4. Power = Current x Potential Difference
P=IV
Now V=IR Sub this into the above: P=

5. Also I=V/R Sub this into P=IV

6. Energy transferred = Power x time (Work done) W = Pt =
Finally:
Energy transferred = Power x time
(Work done)
W = Pt =
(Use P=IV)

7. 15 min Practice Qu’s Pg107

8. Fuse wires
Connect a short length (<10cm) of thin fuse wire to a 12V supply.
CAUTION – Use a heat proof mat
-Only turn powerpack on when whole circuit connected

9. Fuse Wires
-Designed to melt if the current gets too high.
-Must have a rating above max current drawn by device – Why? Normally 3A, 13A or 30A in a house (5A, 40A and larger are also available)
Circuits in a house contain a live and neutral wire (see page 109).

10. Paying for electricity:
Why do we pay for electricity?
We pay for electricity in ‘Units’.
1 Unit = 1 Kilowatt-Hour
A Kilowatt-Hour is a unit of energy.
How many Joules are there in 1kWh?

11. A kilowatt-hour is the energy transferred by a 1kW device in 1hour

13. How much do you think a unit costs?
Cost = Power x Time x Cost per unit
(kW) (hours) (pence)
Kettle = 2.2kW Microwave = 800W
TV = 120W Light = 100W
Power shower = 9500W Hair straighteners=300W
Hair dryer = 1800W

14. Gas is also supplied in kilowatt-hours?
Why is it cheaper? (Ignore direct fuel costs)

15. Practice (finish for homework):
All Qu’s pg’s 107, 109, 111

16. What are today's Key Points?