Question

If the maximum kinetic energy of emitted electrons in photoelectric effect is 3.2 × 10^-19 J and the work-function for metal is 6.63 × 10^-19 J, then stopping potential and threshold wavelength respectively are
[Planck's constant, h = 6.63 × 10³⁴ J-s]
[Velocity of light, c = 3 × 10⁸ `"m"/"s"`]
[Charge on electron= 1.6 × 10^-19 C]

Options

• 4V, 6000 Å

• 3V, 4000 Å

• 2V, 3000 Å

• 1V, 1000 Å

Answer 1

2V, 3000 Å

Explanation:

The maximum kinetic energy of emitted photoelectron is

K_max = eV_s

where, V_s = stopping potential.

`=> "V"_"s" = "K"_"max"/"e" = (3.2 xx 10^-19)/(1.6 xx 10^-19)` = 2V

Also, the work-function of a metal is

`phi = 1242/(lambda_0 ("nm"))`eV

`lambda_0 = (1242 xx 1.6 xx 10^-19)/phi` - nm

`=> (1242 xx 1.6 xx 10^-19)/(6.63 xx 10^-19)`nm

= 3000 Å