Question

Calculate the amount of energy that is saved by replacing a 75-watt incandescent light bulb with an 18-watt fluorescent bulb during the 1500-hour life of the incandescent bulb. one watt is the equivalent of one joule of energy used per second.

Answer 1

First of all, let's convert the life duration of the bulb from hours into seconds:

`t=1500 h = 5.4 \cdot 10^6 s`

So now we can calculate the total energy consumed by the first light bulb:

`E_1=Pt = (75 W)(5.4 \cdot 10^6 s)=4.05 \cdot 10^8 J`

While the total energy consumed by the second light bulb is

`E_2=Pt = (18 W)(5.4 \cdot 10^6 s)=9.7 \cdot 10^7 J`

So the total energy saved by replacing the light bulb is

`\Delta E=E_1 - E_2 = 4.05 \cdot 10^8 J-9.7 \cdot 10^7 J=3.08 \cdot 10^8 J`