How Many Photons Does a 25W Monochromatic Light Bulb Emit Per Second?

[soul5]

How many photons per second are emitted by a monochromatic light bulb (650nm) that emits 25 W of power?

W=hfo

hf=Ek + W

P=W/t


is there a way we can find power? how do I solve this question?

 

[Doc Al]

Hint: What's the energy of a single 650nm photon? (This is not a photoelectric effect problem.)

 

[Moetasim]

To solve this question, we can use the equation P = hfN, where P is power, h is Planck's constant, f is the frequency of the light, and N is the number of photons per second. We can rearrange this equation to solve for N, which will give us the number of photons per second emitted by the light bulb.

First, we need to find the frequency of the light. We know that the wavelength is 650nm, so we can use the equation c = fλ, where c is the speed of light (3.00 x 10^8 m/s). Rearranging this equation, we get f = c/λ. Plugging in the values, we get f = (3.00 x 10^8 m/s) / (650 x 10^-9 m) = 4.62 x 10^14 Hz.

Next, we can plug this frequency value into the equation P = hfN and solve for N. We also need to convert the power from watts to joules/second, so we multiply 25 W by 1 J/s. This gives us:

25 J/s = (6.626 x 10^-34 J*s)(4.62 x 10^14 Hz)N

Solving for N, we get N = 3.23 x 10^19 photons/second.

Therefore, a monochromatic light bulb emitting 25 W of power at a wavelength of 650nm would emit approximately 3.23 x 10^19 photons per second.