How many photons of light are being produced by a 100 watt light bulb in one second?

Question

So the answer is 100, I really dont understand how you got that answer.

Answer 1

( 6.626*10^-34 J*s * frequency )/time= watts per photon

watts per photon / watts = photons... just know what your wavelength is.

Answer 2

1

Answer 3

They've got it pretty much right. (No, not the 100, heh). Since any photon's energy is fixed by its color (frequency or wavelength, since speed is constant) you need to know both the color and the energy being emitted to get the count. Using the average color, yellow, is pretty good - unless you're up to the calculus and know the shape of the whole spectrum being given off by the bulb. 100 watts of blue light is about half the photons as 100 watts of red so thats why the light's color matters. Anyway, if you don't have the spectrum, you probably aren't expected to look it up, so use the yellow color as suggested. It will be a HUGE number.

Answer 4

Photons In Light

Answer 5

Let's estimate it this way:

A standard 100 watt light bulb is only about 8% efficient at producing visible light. The rest goes into heat.

A typical visible photon energy is = hf, or about 6.6 x 10^-34 * 0.5*10^15 Joules = 3.3 x 10^-19 Joules

With only 8 watts of light coming out, the approximate number of photons is 8 watts / (3.3 x 10^-19 Joules), or about 2.4 x 10^19 photons per second.

The number would vary somewhat according to light bulb type, color and efficiency, or if we wanted to include the number of infrared photons in our count.

Wouldn't it be nice if we could ignore the efficiency of our light bulbs when the power bill comes each month? What's a factor of 12x among friends?

Answer 6

The energy of a photon is E = hv, where h is Planck's constant, 6.626 x 10^-34 J-s, and v is the frequency. The frequency of light is equal to c/k, where c is the speed of light, 3 x 10^8 m/s, and k is the wavelength. The average wavelength of visible white light is 550 nm. So the average energy of a photon is hc/k = 3.614 x 10^-19 J. 100 watts means 100 joules per second, so the number of photons emitted in one second should be 100 / (3.614 x 10^-19) = 2.767 x 10^20.

Answer 7

Steps to take:

1) find the frequency, v, of light from the lightbulb. This should be around 3-7*10^14 cycles per second.

2) Find the energy of each photon. This is h*v, where h is Planck's constant 6.67*10^(-34) Js.

3) Find the total amount of energy from the lightbulb each second. Since a watt is one Joule per second, this is easy: 100 J.

4) Divide the total energy released by the energy of each photon. This will give your final answer.

Answer 8

E=hf for photons
100

Answer 9

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Answer 10

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