What comes to mind when you think of POWER

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Presentation transcript:

What comes to mind when you think of POWER

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

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

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

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

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

15 min Practice Qu’s Pg107

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

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).

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?

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

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

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

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

What are today's Key Points?