You have two lightbulbs or different power and color, as indicated in (Figure 1)

ID: 1555678 • Letter: Y

Question

You have two lightbulbs or different power and color, as indicated in (Figure 1). One is a 150-W red bulb, and the other is a 40-W blue bulb. Which bulb emits more photons per second? 150-W red bulb 40-W blue bulb Which bulb emits photons of higher energy? 150-W red bulb 40-W blue bulb Part C Calculate the number of photons emitted per second by each bulb. Take lambda_red = 640 nm and lambda_blue = 430 mm (Most of the electromagnetic radiation given off by incandescent lightbulbs is in the infrared portion of the spectrum. For the purposes of this problem, however assume that all of the radiated power is at the wavelengths indicated.) Express your answers using two significant figures separated by a comma.

Explanation / Answer

Energy of a single photon, E = h = hc/

where h = Planck's constant

= frequency of the light source = c/

= wavelength of the light source

c = speed of light = 3×108m/s

Part A

Now, a red bulb photon has energy, Ered = hc/red , where red = wavelength of the red light = 640nm

So, Ered = [(6.63×10-34 m2 kg / s) (3×108m/s)]/(640×10-9m) = 3.1×10-19J

Now, the red bulb has power = 150W = 150J/s

So number of photons emitted by red bulb per second = (150J/s)/(3.1×10-19J) = 4.84×1020/s

Similarly a blue bulb photon has energy, Eblue = hc/blue, where blue = 430nm

So, Eblue = [(6.63×10-34 m2 kg / s) (3×108m/s)]/(430×10-9m) = 4.62×10-19J

Now, the blue bulb has power = 40W = 40J/s

So number of photons emitted by blue bulb per second = (40J/s)/(4.62×10-19J) = 8.66×1019/s

So we conclude that the 150W red bulb emits more photons per second.

Part B

from Part A we see that:

Ered = 3.1×10-19J and

Eblue = 4.62×10-19J

Thus it's clear that the 40W blue vulb emits photons of higher energy.

Part C

again from Part A, we see that:

the number of photons emitted by red bulb per second = (150J/s)/(3.1×10-19J) = 4.84×1020/s, and

the number of photons emitted by blue bulb per second = (40J/s)/(4.62×10-19J) = 8.66×1019/s

This concludes the answer. But you are always welcome for more clarification if you need..!!!!

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You have two light bulbs of different power and color, as indicated in the figur

You have two lightbulbs or different power and color, as indicated in (Figure 1)

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You have two lightbulbs or different power and color, as indicated in (Figure 1)

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