Calculating Your Electricity Bill

The unit of electrical energy is the kilowatt-hour (kwh). This represents the work done when an appliance rated at one kilowatt of power is operated for one hour. The electric meter records the number of kilowatt-hours used. This is then multiplied by the rate per kwh to figure the cost. If the rate is 5 cents per kiloatt-hour, and you use 100 kwh, your bill will be 500 cents (100 x .05) or $5.00.

The meter at right reads: 19,109 kwh [How To Read Your Electric Meter]

volts x amps = watts

SAMPLE PROBLEM

Find the total power of the following appliances: a toaster that draws a current of 5 amps on a 115-volt line; an electric stove that uses a 5-amp current on a 230-volt line; and ten 100-watt light bulbs.

SOLUTION:

Step 1. The toaster uses 5 amps at 115 vots. Power = volts x amps = 115 x 5 = 575 watts

Step 2. The stove uses 5 amps at 230 volts. Power = volts x amps = 230 x 5 = 1,150 watts

Step 3. Ten lamps at 100 watts each. Power = 10 x 100 = 1,000 watts

Step 4. The total power is 575 + 1,150 + 1000 = 2,725 watts, or 2.725 kilowatts.

(Source: Modern Physical Science, 1966)