Question

A microwave oven has a power requirement of 1238 W. A frozen dinner requires 6.9 minutes to heat on full power. (a) How much electrical energy in (kWh) is used?

(b) If the cost of electricity is 12 cents per kWh, how much does it cost to heat the dinner?

Answer 1

a) 0.14237 kWh

b) 1.70844 cents

Step-by-step explanation:

Electrical energy is defined as amount of work done per unit time.

or

The product of power and time is energy

a) Power of the microwave is 1238 W

Time the microwave is operating is 6.9 minutes

Converting to hours

6.9/60 = 0.115 hours

Power

P = 1238 × 0.115

⇒P = 142.37 Wh = 0.14237 kWh

∴ Electrical energy used is 0.14237 kWh

a) 1 kWh requires 12 cents

Cost required to use microwave

0.14237×12 = 1.70844 cents

∴ Cost to heat the dinner is 1.70844 cents

Answer 2

(a) 142.37 kWh (b) 1708.44 cents

Step-by-step explanation:

It is given that the microwave has a power requirement of 1238 W

The frozen dinner takes 6.9 minutes to heat

So time t =6.9 minutes
`=(6.9)/(60)=0.115hour`

(a) The total energy used = power ×time = 1238×0.115=142.37 kWh

(B) The cost of the electricity is 12 cents per kWh

So total cost = 12×142.37=1708.44 cents