Find the velocity of photoelectrons liberated by electromagnetic radiation of wavelength $λ = 18.0 nm$ from stationary ${He}^{+}$ ions in the ground state. ( $h = 4.14 \times 10^{- 15} eV s & c = 3 \times 10^{8} m s^{- 1}$ )

Important Questions on Dual Nature of Matter and Radiation

HARD

JEE Main/Advance

IMPORTANT

Alpha Question Bank for Engineering: Physics>Chapter 32 - Dual Nature of Matter and Radiation>Exercise - 4>Q 2

(I) Find the maximum wavelength of light which can ionize a

H

-atom in the ground state.
(II) Light of wavelength

λ

is incident on a

H

-atom which is in its first excited state. Find the kinetic energy of the electron coming out.

HARD

JEE Main/Advance

IMPORTANT

Alpha Question Bank for Engineering: Physics>Chapter 32 - Dual Nature of Matter and Radiation>Exercise - 4>Q 3

In a photo electric effect set - up, a point source of light of power

3.2 \times 10^{- 3} W

emits mono energetic photons of energy

5.0 eV

. The source is located at a distance of

0.8 m

from the centre of a stationary metallic sphere of work function

3.0 eV

& of radius

8.0 x 10^{- 3} m

. The efficiency of photo electrons emission is one for every

10^{6}

incident photons. Assume that the sphere is isolated and initially neutral, and that photo electrons are instantly swept away after emission.
(a) Calculate the number of photo electrons emitted per second.
(b) Find the ratio of the wavelength of incident light to the De - Broglie wave length of the fastest photo electrons emitted.
(c) It is observed that the photo electron emission stops at a certain time