## Question

When a certain metal was irradiated with a light of frequency

3.2 × 10^{16 }Hz, the photo-electrons had twice the kinetic energy as emitted when the same metal was irradiated with light of frequency 2.0 × 10^{16} Hz. Calculate the threshold frequency (*v _{0}*) of the metal.

### Solution

Kinetic energy of photoelectrons emitted = *hv – hv _{0}* =

*h*(

*v – v*)

_{0}

.

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