A monochromatic flashlight emits light of power at wavelength

PHYSICS · Single correct · A Level · Physics · Particles and radiation · Particles and radiation

Problem

A monochromatic flashlight emits light of power

P

at wavelength

\lambda

. Which of the following expressions gives the number of photons

N

emitted each second in terms of

P,\,\lambda

, the speed of light

c

, and Planck’s constant

h

? (a)

N = 2\pi\,\dfrac{P\,\lambda}{h c}

(b)

N = \dfrac{P\,\lambda}{2 h c}

(c)

N = \dfrac{P\,\lambda}{h c}

(d)

N = 3\,\dfrac{P\,\lambda}{h c}