Q: when the light of frequency 2ν_{0} (Where ν_{0} is threshold frequency ) is incident on a metal plate , the maximum velocity of electron emitted is v_{1} . When the frequency of incident radiation is increased to 5ν_{0} , the maximum velocity of electron emitted from the same plate is v_{2} . The ratio of v_{1} to v_{2}

(a)4:1

(b)2:1

(c)1:4

(d)1:2

Ans: (d)

Sol: In case (i)

h.2ν_{0} = h.ν_{0} + (1/2)m v_{1}^{2}

h.ν_{0} = (1/2)m v_{1}^{2} …(i)

In case (ii)

h.5ν_{0} = h.ν_{0} + (1/2)m v_{2}^{2}

h.4ν_{0} = (1/2)m v_{2}^{2} …(ii)

Dividing equations (i) and (ii) we get

v_{1}/v_{2} = 1/2