Question

If a student leaves 100-w lightbulb on In his room for 1 h, how many kilowatt-hour of electricity does the bulb use?

Answer 1

1)  0.1 kWh

Explanation:

The power of the lightbulb is:

$P = 100 W=0.1 kW$

The energy used by the lightbulb is equal to the product between the power (P) and the time (t):

$E=Pt$

Since the bulb has been left on for t = 1 h, the total electrical energy used is

$E=Pt=(0.1 kW)(1 h)=0.1 kWh$

2) $ 0.018

Explanation:

The company charges $0.18 per each kilowatt-hour. So, we can find the total cost charged for using 0.1 kWh of electricity by setting the following proportion:

$0.18 : 1 kWh = x : 0.1 kWh

And solving for x, we find

$x=\frac{\ 0.18 \cdot 0.1kWh}{1 kWh}=\ 0.018$