In a circuit, power is the rate that electricity is used

P= E/t The unit for power is a watt (joules per sec)

There are other equations where power can be found these are:

P=VIt (since E=VI) If given resistance use the following

equations: P=I2R or P=V2/R

What is the resistance of a 600W kettle that draws a current of 5.00 A?

The power rating shown on electrical appliances gives a comparative indication of the cost of operating these appliances

The energy consumed by an electrical appliance depends on its power rating and length of time operating.

The EnerGuide label is a tool to help you make an energy-wise choice when buying a new appliance. It shows how much energy appliances consume in a year of normal service and makes it easy to compare the energy efficiency of each model to others of the same size and class.

EnerGuide ratings for major household Appliances range from the most energy-efficient (i.e with the lowest energy consumption) to the least energy-efficient (i.e with the highest energy consumption) in a given size and type category.

For major appliances, an indicator arrow on the left side of the EnerGuide scale means lower operating costs and long-term savings.

Check your electricity bill to find out what you're paying per kWh of electricity. Multiply the price (in $/kWh) with the big, bold kWh per year number on the EnerGuide label. The result will tell you how much you should budget on an annual basis to operate the appliance once it is installed in your home.

We pay for all of the electricity that we use.

We usually pay a few cents for a kilowatt hour

1 kilowatt-hour (1-kW-h) equals the energy used to operate a device rated at 1 kilowatt for one hour (or the energy dissipated in 1 hour by a load with a power of 1 kW)

1 kW-h= 3.6 x 106 J 1 kW-h= 3.6 MJ

The energy consumed can be calculated using:

E=Pt E= energy consumed (in kW-h) P= amount of Power (in kW) T=time (in hours)

Calculate the electric energy (in kW-h) used in operating a 40 W bulb for 30 mins?

2. Estimate the cost of watching TV for 3 hrs. A typical color TV has a power of 150W. Use a unit cost of 6 cents per kilowatt-hour.

Power and cost of electricity handout