Question

Which relationship gives the number of photons emitted per second by a laser of power \[P\] when each photon has energy \[E\]?

Options

• \[P=N+E\quad\Rightarrow\quad N=P-E\]

• \[P=NE\quad\Rightarrow\quad N=\frac{E}{P}\]

• \[P=\frac{N}{E}\quad\Rightarrow\quad N=PE\]

• \[P=NE\quad\Rightarrow\quad N=\frac{P}{E}\]

Answer 1

Power is the total photon energy emitted per second, so \[P=NE\]. Dividing power by the energy of one photon gives \[N=\frac{P}{E}\], the number emitted per second.