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

Answer:

a. E=1440KJ

b. E=360KJ

c. E=1.8 J

Explanation:

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

so, for the lightbulb

$100W= \frac{Energy}{3600s*4}\\Energy=100W*14400s\\ E=1440000J =1440KJ$

Analogously, for the microwave

$1200W= \frac{Energy}{60s*5}\\Energy=1200W*300s\\ E=360000J =360KJ$

Now, I have to express the efficiency as Heat energy / power * 100 so$1.8= \frac{Heat Energy}{100W}*100\\Heat Energy=1.8J$

Done