A typical smaall laser has a power of 0.5mW= 5*10^-4J/s. How many photons are emitted each second by the laser?

Power = (photons/sec)*(energy per photon)

To get an answer, you need to know what the wavelength (or frequency) is. This is what determines the photon energy.

Most, but not all, small lasers are red, so you could assume a wavelength of 630*10^-9 m. That would make the photon
3.1*10^-19 J.

Photons/s = (5*10^-4 J/s)/(3.1*10^-19 J)
= ______

To calculate the number of photons emitted per second by a laser, you can use the equation:

Number of photons = Power of the laser / Energy of each photon

Given that the power of the laser is 0.5mW (which is equivalent to 5 * 10^-4 J/s), and we know that 1 photon has an energy of Planck's constant (h) multiplied by the frequency of the laser (ν):

Energy of each photon = h * ν

Now, we need to determine the frequency of the laser. Assuming that the laser emits light in the visible range, we can use the equation:

ν = c / λ

where ν represents the frequency of light, c represents the speed of light (approximately 3 * 10^8 m/s), and λ represents the wavelength of light emitted by the laser.

Without further information, it is difficult to determine the exact wavelength of the laser. However, a common wavelength for visible lasers is 500 nm (5 * 10^-7 m).

Plugging these values into the equation, we get:

ν = (3 * 10^8 m/s) / (5 * 10^-7 m)
ν ≈ 6 * 10^14 Hz

Now, substituting the frequency back into the equation for the energy of each photon, we have:

Energy of each photon = (6.626 * 10^-34 J*s) * (6 * 10^14 Hz)
Energy of each photon ≈ 4 * 10^-19 J

Finally, we can find the number of photons emitted by the laser each second:

Number of photons = Power of the laser / Energy of each photon
Number of photons ≈ (5 * 10^-4 J/s) / (4 * 10^-19 J)
Number of photons ≈ 1.25 * 10^15 photons/s

Therefore, a typical small laser with a power of 0.5mW emits approximately 1.25 * 10^15 photons per second.