Question

Define threshold frequency.

Answer 1

Hint – Whenever a beam of photons strikes a metal surface then electrons are emitted out of the metal surface but these electrons are not emitted out as soon as the electrons strike in fact it depends upon a vivid number of factors one of which is the threshold frequency. Use this concept to approach the solution.

Complete step-by-step solution-

Threshold frequency: Threshold frequency is the minimum frequency of the incident radiation below which photoelectric emission is not possible irrespective of the intensity of the incident radiation.
Photoelectric effect
Photoelectric effect is the emission of the electrons when a ray of light coming from the source such as SUN (i.e. electromagnetic radiation coming from the SUN) is incident on the material such as (any metal piece).
Emitted electrons are called photoelectrons.
So the threshold frequency is the frequency of the light which carries enough energy to dislodge an electron from an atom (i.e. release an electron from the metal which contains electrons in rest position, every metal contains the electrons).
So if the frequency of the incident radiation is less than the threshold frequency of the metal because of this no electrons have been released from the metal as electrons gain no kinetic energy or not enough kinetic energy to dislodge an electron from the atom or metal piece.
As the electrons does not gain enough velocity so that it does not gain enough kinetic energy as kinetic energy (K.E) is half times the mass (m) multiplied by the square of the velocity (v) of the electrons.
$K.E = \dfrac{1}{2}m{v^2}$
So this is the required answer.

Note – The main reason behind the emission of the electrons from the metal surface when a wave of light hits a metal surface is due to the dual behavior of light since light can act as both wave and particle, so this depicts that light is composed of photons or energy quanta. These photons when hit the surface transfer energy to the surface electrons and thus making the emission possible.