Question

When monochromatic light falls on a photosensitive material, the number of photoelectrons emitted per second is $n$ and their maximum kinetic energy is $K_{max}$ . If the intensity of incident light is doubled, then:

• A. $n$ is doubled but $K_{max}$ remains same
• B. $K_{max}$ is doubled but $n$ remains same
• C. both $n$ and $K_{max}$ are doubled
• D. both $n$ and $K_{max}$ are halved

Answer 1

Answer: (A)

$n$ is doubled but $K_{max}$ remains same

Maximum Kinetic energy of emitted photoelectrons is given by:

$K_{max}=h\nu -\varphi$

Hence, it is dependent mainly on the energy ( i.e. frequency) of incident photon. On doubling the intensity, $K_{max}$ remains the same.

Every photon having energy more than the work function of the metal has the capacity to emit one photoelectron. Hence, on doubling the intensity, number of photoelectrons emitted in unit time ($n$) doubles.