Ncert Exercises & Solutions

2.12 Electrons are emitted with zero velocity from a metal surface when it is exposed to radiation of wavelength 6800 Å. Calculate threshold frequency (ν0 ) and work function (W0 ) of the metal.

Threshold wavelength of radiation

(λ_{0}) = 6800 \overset{o}{A}

= 6800 ×

10^{- 10}

m
Threshold frequency

(V_{0})

of the metal

\approx \frac{c}{λ_{0}} = \frac{3 x 10^{8} m / s}{6.8 x 10^{- 7} m} = 4.41 x 10^{14} s^{- 1}

Thus, the threshold frequency of the metal is 4.41 × 1014 s
–1
.
Hence, work function

(W_{0})

of the metal = hν0
= (6.626 ×

10^{- 34}

Js) (4.41 ×

10^{14}

s^{- 1}

)
= 2.922 ×

10^{- 19}

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