Question

A photon of wavelength 3315 Å falls on a photocathode and an electron of energy 3 x 10^-19 J is ejected. The threshold wavelength of photon is [Planck's constant (h) = 6.63 x 10^-34 J.s, velocity of light (c) = 3 x 10⁸ m/s] ____________.

Options

• 5000 Å

• 3315 Å

• 6630 Å

• 1130 Å

Answer 1

A photon of wavelength 3315 Å falls on a photocathode and an electron of energy 3 x 10^-19 J is ejected. The threshold wavelength of photon is 6630 Å.

Explanation:

`phi_0 = "hc"/lambda - "E"`

`= (6.63 xx 10^-34 xx 3 xx 10^8)/(3315 xx 10^-10) - 3 xx 10^-19)`

`= (6 - 3) xx 10^-19`

`= 3 xx 10^-19`

`lambda_0 = "hc"/phi_0`

`= (6.63 xx 10-34 xx 3 xx 10^8)/(3 xx 10^-19)  approx 6630  Å`