12 physics unit 8 em

The wavelength λe of an electron and λp of a photon of same energy E are related by

• λp ∝ λe

• λp ∝ √λe

• λp ∝1/√λe

• λp ∝ λe²

In an electron microscope, the electrons are accelerated by a voltage of 14 kV. If the voltage is changed to 224 k V, then the de Broglie wavelength associated with the electrons would

• increase by 2 times

• decrease by 2 times

• decrease by 4 times

• increase by 4 times

A particle of mass 3 ×10^–6 g has the same wavelength as an electron moving with a velocity 6 × 10⁶ m s^-1 . The velocity of the particle is

• 1.82 ×10⁻¹⁸ m s^-1

• 9 ×10⁻² m s^-1

• 3 ×10⁻³¹ m s^-1

• 1.82 ×10⁻¹⁵ m s^-1

When a metallic surface is illuminated with radiation of wavelength λ, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2λ, the stopping potential is V/4 . The threshold wavelength for the metallic surface is

• 4λ

• 5λ

• 5λ/2

• 3λ

If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the emitted electron is (Take h = 6.6 ×10^–34 Js)

• < 2.75 ×10⁻⁹ m

• ≥ 2.75 ×10⁻⁹ m

• ≤ 2.75 ×10⁻¹² m

• < 2.5 ×10⁻¹⁰ m

A photoelectric surface is illuminated successively by monochromatic light of wavelength λ and λ/2 . If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function at the surface of material is

• hc/λ

• 2hc/λ

• hc/3λ

• hc/2λ

In photoelectric emission, a radiation whose frequency is 4 times threshold frequency of a certain metal is incident on the metal. Th en the maximum possible velocity of the emitted electron will be

• √2v_⁰/m

• √6hv₀/m

• √hv₀/m

• √ hv_o/2m

Two radiations with photon energies 0.9 eV and 3.3 eV respectively are falling on a metallic surface successively. If the work function of the metal is 0.6 eV, then the ratio of maximum speeds of emitted electrons will be

• 1:4

• 1:3

• 1:1

• 1:9

A light source of wavelength 520 nm emits 1.04 × 10¹⁵ photons per second while the second source of 460 nm produces 1.38 × 10¹⁵ photons per second. Then the ratio of power of second source to that of first source is

• 1.00

• 1.02

• 1.5

• 0.98

The mean wavelength of light from sun is taken to be 550 nm and its mean power is 3.8 × 10²⁶ W. The number of photons received by the human eye per second on the average from sunlight is of the order of

• 10⁴⁵

• 10⁴²

• 10⁵⁴

• 10⁵¹