# Light of Frequency 7.21 × 1014 Hz is Incident on a Metal Surface. Electrons with a Maximum Speed of 6.0 × 105 M/S Are Ejected from the Surface. What is the Threshold Frequency for Photoemission of Electrons? - Physics

Light of frequency 7.21 × 1014 Hz is incident on a metal surface. Electrons with a maximum speed of 6.0 × 105 m/s are ejected from the surface. What is the threshold frequency for photoemission of electrons?

#### Solution

Frequency of the incident photon, v = 488 nm = 488 xx 10^(-9) m

Maximum speed of the electrons, v = 6.0 × 105 m/s

Planck’s constant, h = 6.626 × 10−34 Js

Mass of an electron, m = 9.1 × 10−31 kg

For threshold frequency ν0, the relation for kinetic energy is written as:

1/2 mv^2 = h(v - v_0)

v_0 = v - (mv^2)/(2h)

= 7.21 xx 10^14 - ((9.1 xx 10^(-31) )xx (6xx10^(5))^2)/(2xx(6.626 xx 10^(-34)))

Therefore, the threshold frequency for the photoemission of electrons is 4.738 xx  10^14 Hz

Concept: Photoelectric Effect and Wave Theory of Light
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#### APPEARS IN

NCERT Class 12 Physics Textbook
Chapter 11 Dual Nature of Radiation and Matter
Q 10 | Page 408