A 100-watt light bulb radiates energy at a rate of 100 J/s. (The watt, a unit of power or energy over time, is defined as 1 J/s J/s.) If all of the light emitted has a wavelength of 525nm 525nm, how many photons are emitted per second? Express your answer to three significant figures.

Approximately (assumption: wavelength is measured in vacuum, where the speed of light is approximately .)

Explanation:

Convert the unit of wavelength to meters:

.

Assume that the wavelength is measured in vacuum, where the speed of light is approximately . Calculate the frequency of this light from its wavelength:

.

The Planck's Constant can help find the energy of a photon given its frequency. Look up this constant to more than three significant figures:

.

Calculate the energy of one such photon:

.

Calculate the number of these photons that of energy can produce under the assumption of conversion:

.

(Rounded to three significant figures.)