The maximum velocities of the photoelectrons ejected are v and 2v for the incident light of wavelength 400 nm and 250 nm on a metal surface respectively. The work function of the metal in terms of Planck's constant h and velocity of light c is

• hc × 10⁶ J

• 2 hc × 10⁶ J

• 1.5 hc × 10⁶ J

• 2.5 hc × 10⁶ J

If the frequency of incident light falling on a photosensitive metal is doubled, the kinetic energy of the emitted photoelectron is

• unchanged

• halved

• doubled

• more than twice its initial value

The work functions of two metals are 2.75 eV respectively. If these are irradiated by photons of energy 3 eV, the ratio of maximum momenta of the photoelectrons emitted respectively by them is

• 1 : 2

• 1 : 3

• 1 : 4

• 2 : 1

The maximum kinetic energy of photoelectrons

• depends on collector plate

• is independent of emitter plate material

• is independent of frequency of incident radiation

• depends on the frequency of light source and the nature of emitter plate material

If e/m of electron is 1.76 x 10¹¹ C kg^-1 and the stopping potential is 0.71 V, then the maximum velocity of the photo-electron is

• 150 kms^-1

• 200 kms^-1

• 500 kms^-1

• 250 kms^-1

If m is the mass of an electron and c is the speed of light, the ratio of the wavelength of a photon of energy E to that of the electron of the same energy is

• $\mathrm{c}\sqrt{\frac{2\mathrm{m}}{\mathrm{E}}}$

• $\sqrt{\frac{2\mathrm{m}}{\mathrm{E}}}$

• $\sqrt{\frac{2\mathrm{m}}{\mathrm{cE}}}$

• $\sqrt{\frac{\mathrm{m}}{\mathrm{E}}}$

When a metallic surface is illuminated by a light of wavelength λ, the stopping potential for the photoelectric current is 3 V. When the same surface is illuminated by light of wavelength 2λ, the stopping potential is 1 V, the threshold wavelength for this surface is

• 4 λ

• 3.5 λ

• 3 λ

• 2.75 λ

The threshold wavelength for photoelectric emission from a material is 4800 $\stackrel{\circ }{\mathrm{A}}$. Photoelectrons will be emitted from the material, when it is illuminated with light from a

• 40 W blue lamp

• 40 W green lamp

• 100 W red lamp

• 100 W yellow lamp

29.

When a monochromatic point source of light is at a distance 0.2 m from a photoelectric cell, the saturation current and cut-off voltage are 12.0 mA and 0.5 V. If the same source is placed 0.4 m away from the photoelectric cell, then the saturation current and the stopping potential respectively are

• 4 mA and 1 V

• 12 mA and 1 V

• 3 mA and 0.5 V

• 12 mA and 0.5 V

A photodetector used to detect the wavelength of 1700 nm, has energy gap of about

• 0.073 eV

• 1.2 eV

• 0.73 eV

• 1.16 eV