A caesium photocell, with a steady potential difference of 60 V across it, is illuminated by a bright point source of light 50 cm away. When the same light is placed 1 cm away, the photoelectrons emitted from the cell

• are half as numerous

• are one quarter as numerous

• each carry one quarter of their previous energy

• each carry one quarter of their

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

• 
• 

• 3

• 3

A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is U₁, at wavelength 500 nm is U₂ and that at 1000 nm is U₃. Wien's constant, b = 2.88 x 10⁶ nmK. Which of the following is correct?

• U₃ = 0

• U₁ > U₂

• U₂ > U₁

• U₂ > U₁

A radiation of energy 'E' falls normally on a perfectly reflecting surface. The momentum transferred to the surface is 
(c = velocity of light)

An electron of mass m and a photon have the same energy E. The ratio of de-Broglie wavelength associated with them is,

Which of the following figures represent the variation of particle momentum and the associated de-Broglie wavelength?

If the momentum of an electron is chagned by p, then the de-Broglie wavelenght associated with it changes by 0.5%. The initial momentum of electron will be

• 200p

• 400p

• p/200

• p/200

Two radiations of photon energies 1 eV and 2.5 eV, successively illuminate a photosensitive metallic surface of the maximum speeds of the emitted electrons is

• 1:4

• 1:2

• 1:1

• 1:1

69.

An α- particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of 0.25 Wb/m². The de-Broglie wavelength associated with the particle will be

• 1 A^o

• 0.1 A^o

• 10 A^o

• 10 A^o

Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

• 4 x 10¹⁵ Hz

• 5 x 10¹⁵ Hz

• 1.6 x10¹⁵ Hz

• 1.6 x10¹⁵ Hz