Q. 263.7( 3 Votes )

# Ultraviolet light

Answer :

Given:

Wavelength of light, λ = 2271 Å = 2271 × 10-10m

Power of mercury source, E = 100 Js-1

Stopping potential, Vs = -1.3 V

Let frequency of light = v

Work function, Φ0 is given by,

Φ0 = hv-eVs

Φ0 = Where,

h = Planck’s constant = 6.6 × 10-34Js

c = speed of light = 3 × 108m

λ = wavelength of light

e = charge on each electron = 1.6 × 10-19C

Φ0 = Φ0 = 6.64 × 10-19J

Φ0 = (6.64/1.6) × 10-19 eV = 4.15 eV

Let v0 be the threshold frequency of the metal,

Φ0 = hv0

v0 = Φ0/h

v0 = 6.6 × 10-19/ 6.6 × 10-34

v0 = 1.00. × 10-15 s-1

Wavelength of red light, λ’ = 6323 × 10-10m

Frequency of red light can be given as,

v' = c/λ’

v’ = v’ = 4.74 × 1014 Hz

Since the threshold frequency is greater than the frequency of red light, the photocell will not respond to the red light produced.

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