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?

Photoelectric equation

K. E_max = hv – hv_{0 ……………………………………….}equ.01

Where K.E_max = maximum kinetic energy of the photoelectron

h = plank’s constant

v = frequency of photon

v₀ = threshold frequency

K. E_max = 1/2 mv² _max ........................................equ.02

Where ‘m’ = mass of the electron = 9.1 × 10^-31 kg

V_max = maximum speed of photoelectrons

From equ.01 and equ.02

1/2 mv² _max = hv - hv₀

∴ v₀ = v - 1/2 mv² _max / h

⇒

⇒ v₀ = 7.21 × 10¹⁴ –2.47 × 10¹⁴

⇒ v₀ = 4.74 × 10¹⁴ Hz

Threshold frequency for photoemission is equal to 4.74 × 10¹⁴ Hz.