Question

A lightbulb has a power of 100 W and is used for 4 hours. A microwave has a power of 1200 W and is used for 5 minutes. How much energy is used by the lightbulb? How much energy is used by the microwave? The lightbulb has an efficiency of 1.8%. How much heat energy does the lightbulb produce in 4 hours?

Answer 1

a. E=1440KJ

b. E=360KJ

c. E=1.8 J

Step-by-step explanation:

I have the power (Watts) is expressed as Energy (Joules) / Time (seconds), also I have to
`1hour * (60min)/(1hour)*(60s)/(1min)\\1h=3600s`

so, for the lightbulb

`100W= (Energy)/(3600s*4)\\Energy=100W*14400s\\ E=1440000J =1440KJ`

Analogously, for the microwave

`1200W= (Energy)/(60s*5)\\Energy=1200W*300s\\ E=360000J =360KJ`

Now, I have to express the efficiency as Heat energy / power * 100 so
`1.8= (Heat Energy)/(100W)*100\\Heat Energy=1.8J`

Done