ELECTRIC BILLS

ELECTRIC BILLS

YOUR ELECTRIC BILL

Cost of Electrical Energy Energy = W = Pt

Unit: Joules or kWhr

1kWhr = 3.6 x 106J

*The electric company uses the kWhr due to the large amount of energy used in the home.

EXAMPLE: A television draws 5.0Amps of current

when operated on 120V.

a) What is the power rating of the television?

P = VI

P = 120V(5Amps)

P = 600W =0.6kW

B) What amount of energy is consumed by the television over 30, 5hr days?

W=Pt

W= 0.6kW(30days)(5hr/day)

W= 90kWhr

C) At $.11 per kWhr, what is the cost of operating the television for this time?

cost = 90kWhr( $.11/kWhr)

cost = $9.90

You pay for electrical energy measured in kWhr.

SHORT CIRCUITS

A circuit that has little to no resistance.

Current always takes the path of least resistance. The current in the extra wire across R1 will bypass the resistor.

SAFETYToo many resistances in parallel will decrease the total resistance to a very low level. This creates a short circuit.

Circuit breakers

If current is too high a circuit breaker will mechanically open the circuit and stop the flow of current.

FUSES

If current is too high, it melts a thin piece of wire in the fuse which stops the flow of current.