Question

A 100-watt lightbulb 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.) If all of the light emitted has a wavelength of 520nm, how many photons are emitted per second

Answer 1

Answer:

2.62x10²⁰ photons are emitted per second.

Explanation:

The number of photons emitted per second can be found using the following equation:

$E = \frac{hc}{\lambda}$   (1)

Where:

h: is the Planck's constant = 6.62x10⁻³⁴ J.s

c: is the speed of light = 3.00x10⁸ m/s

λ: is the wavelength = 520 nm

E: is the energy = 100 J/s

Equation (1) gives the energy for a single photon, so if we have more than one we need to use the term "n" to indicate the number of photons:

$E = \frac{nhc}{\lambda}$  

By solving the above equation for n we have:

$n = \frac{E \lambda}{hc} = \frac{100 J/s*520 \cdot 10^{-9} m}{6.62 \cdot 10^{-34} J.s*3.00 \cdot 10^{8} m/s} = 2.62 \cdot 10^{20} photons/s$    

Therefore, 2.62x10²⁰ photons are emitted per second.

 

I hope it helps you!