Question 1 (Worked Example) Define Power and how it is calculated.
Power is the rate that Energy (joules) is converted form one form (electrical) to another (heat).
It is calculated from 4.8 J for each ml of water increased by 1 degree, or VxI. It has units of watts.
Question 2 What is the formula for Energy. What units are used to buy Energy.
Question 3 (Worked Example) Zany has a 1kW pool pump that operates from 8am to 10 am every day of the year. Electricity cost $ 0.25 per kWhr. What is the annual use of energy? How much does this cost Zany?
P = E/t
E = P x t
E = 1kW x 2hr x 365
E = 730 kWhr
Cost = E x rate per kWhr
Cost = 730 x 0.25 = $182.50
Question 4 Tom has as 4 bar fridges that use 200 W. How many joules of energy does he use in a year? Why is kWhr the normal unit seen on his bill?
Question 5 (Worked Example)
Anne can use 6 V on a 10 ohm light, or 12 volt on a 40 ohm light. Which produces most power? If the leads are 1 ohm, which is the brighter light?
Thus they have the same brightness. Power loss can be calculated by working out the total resistance, the current and voltage drop and then the Power loss.
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