Question

electromagnetic radiations having wavelength = 310 angstrom are subjected to a metal sheet having work function =12.8 Ev. What will be the velocity of photoelectrons with be the velocity of photoelectrons with maximum kinetic energy .

Answer 1

K. E = hf - Ф

h = planks constant = 6.62 × 10⁻³⁴

f = c/y

c = speed of light in air = 3.0 × 10⁸ m/s

y = 3.10 × 10⁻⁹m

Ф = 12.8 × 1.6 × 10⁻¹⁹ = 2.016 × 10⁻¹⁸ Joules.

f = (3 × 10⁸) / (3.10 × 10⁻⁹) = 9.6774 × 10¹⁶

hf = 9.6774 × 10¹⁶ × 6.62 × 10⁻³⁴ = 6.41 × 10⁻¹⁷ Joules

K. E = 6.41 × 10⁻¹⁷ - 2.016 × 10⁻¹⁸ = 6.2084 × 10⁻¹⁷ joules.

K. E = 1/2mv²

m = mass of an electron = 9.1 × 10⁻³¹

6.2084 × 10⁻¹⁷ = 0.5 × 9.1 × 10⁻³¹v²

V² = 1.3645 × 10¹⁴

V = 1.1681 × 10⁷ m/s