Alightbulb 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.
a) how much energy is used by the lightbulb?
b) how much energy is used by the microwave?
c) the lightbulb has an efficiency of 1.8%. how much heat energy does the lightbulb produce in 4 hours?

Part a)

As we know that energy is defined as product of power and time

so here for light bulb we know that

Power = 100 W

time = 4 hours

so energy = Power * time

Part b)

Now for microwave we know that

Power = 1200 W

time = 5 hours

so energy = Power * time

Part C)

Light bulb is having efficiency of 1.8%

so it will convert 1.8% energy into light

Rest of the energy will be emitted into heat here

so heat energy is (100 - 1.8)% = 98.2% of total energy

so