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.

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?

Answer 1

a) Energy is used by the light bulb when it is used for 4 hours:1,440,000 Joules.

b) Energy is used by the microwave when it is used for 5 minutes:360,000 Joules

c)1,414,080 Joules of heat energy will be produced by light bulb in 4 hours.

Step-by-step explanation:

Power is defined as ratio of work done per unit time.

`Power=(Energy)/(Time)`

Power of light bulb,P = 100 W

Power of microwave,P' = 1200 W

a) Energy is used by the light bulb when it is used for 4 hours:

Duration of time it is used = T = 4 hours =14,400 s

`Power=(Energy)/(Time)`

`Energy=P* T=100 W* 14,400 s=1,440,000 J`

b) Energy is used by the microwave when it is used for 5 min:

Duration of time it is used = T' = 5 min = 300 sec

`Power=(Energy)/(Time)`

`Energy=P'* T'=1200 W* 300 s=360,000 J`

c) Heat energy produced by light bulb with an efficiency of 1.8%.

Efficiency 1.8% means that light bulb gives 1.8 % of its energy into light energy remaining as heat energy.

Heat energy produced by light bulb = 100% - 1.8 % = 98.2 %

Energy used by the bulb in 4 hours = 1,440,000 J

Heat energy produced by light bulb = 98.2% of 1,440,000 J:

`(98.2)/(100)* 1,440,000 J=1,414,080 J`

1,414,080 Joules of heat energy will be produced by light bulb in 4 hours.

Answer 2

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

`E = 100 * (4* 3600)`

`E = 1.44 * 10^6 J`

Part b)

Now for microwave we know that

Power = 1200 W

time = 5 hours

so energy = Power * time

`E = 1200 * (5* 3600)`

`E = 2.16 * 10^7 J`

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

`Heat = 0.982* 1.44 * 10^6`

`Heat = 1.41 * 10^6 J`