71.

Light with an energy flux of 25 x 10⁴ W/m² falls on a perfectly reflecting surfaces at normal incidence. If the surface area is 15 cm², the average force exerted on the surface is,

• 1.25 x 10^-6 N

• 2.50 x 10^-6 N

• 1.20 x 10^-6 N

• 1.20 x 10^-6 N

When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is,

• 0.65 eV

• 1.0 eV

• 1.3 eV

• 1.3 eV

If the kinetic energy of the particle is increased to 16 times its previous value, the percentage change in the de-Broglie wavelength of the particle is,

• 25

• 75

• 60

• 60

For photoelectric emission from certain metal, the cut-off frequency is v. If radiation of frequency is v. If radiation of frequency 2v impinges on the metal plate, the maximum possible velocity of the emitted electrons will be (m is the electron mass)

In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by

• Increasing the filament current

• decreasing the filament current

• decreasing the potential difference between the anode and filament

• decreasing the potential difference between the anode and filament

In photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding  stopping potential is

• 1.3 V

• 0.5 V

• 2.3 V 

• 2.3 V 

Photoelectric emission occurs only when the incident light has more than a certain minimum

• wavelength

• intensity

• frequency

• frequency

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 of the surface of the material is 

(h = planck's constant, c= speed of light)

• hc/ 2λ

• hc/λ

• 2 hc/λ

• 2 hc/λ

Light of wavelength 500 nm is incident on metal with work function 2.28 eV. The de - Broglie wavelength of the emitted electrons is 

• <2.8 x 10^-10 m 

• <2.8 x 10^-9 m

• > equal  to 2.8 x 10^-9 m

• > equal  to 2.8 x 10^-9 m

The threshold frequency for a photo-sensitive metal is 3.3 x 10¹⁴ Hz. If light of frequency 8.2 x 10¹⁴ Hz is incident on this metal, the cut -off voltage for the photo-electric emission is nearly

• 2 V

• 3 V

• 5 V

• 5 V