91.

A particle of mass 1 mg has the same wavelength as an electron moving with a velocity of 3 x 10⁶ ms^-1. The velocity of the particle is.

(mass of electron = 9.1 x 10^-31 kg)

• 2.7 x 10^-18 ms^-1

•  9 x 10^-2 ms^-1

• 3 x 10^-31 ms^-1

• 3 x 10^-31 ms^-1

Monochromatic light of frequency 6.0 x 10¹⁴ Hz is produced by a laser. The power emitted is 2 x 10^-3 W. The number of photons emitted, on the average, by the source per second is:

• 5 x 10¹⁵

• 5 x 10¹⁶

• 5 x 10¹⁷

• 5 x 10¹⁷

A  5 W source emits monochromatic light of wavelength 5000 A. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. when the source si moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor  of:

• 4

• 8

• 16

• 16

A photo-cell employs photoelectric effect to convert

• change in the frequency of light into a change in electric voltage

• change in the intensity of illumination into a change in photoelectric current

• change in the intensity of illumination into a change in the work function of the photocathode

• change in the intensity of illumination into a change in the work function of the photocathode

When photons of energy hv fall on an aluminium plate (of work function E₀), photoelectrons of maximum kinetic energy K are ejected. If the frequency of the radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be

• K+E₀

• 2K

• K

• K

The momentum of a photon of energy 1 MeV in kg m/s, will be

Young’s double slit experiment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in the air. The refractive index of the medium is nearly

• 1.25

• 1.59

• 1.69

• 1.69

The photoelectric threshold wavelength of silver is 3250 × 10^–10 m. The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength 2536 × 10^–10 m is

(Given h = 4.14 × 10^–15 eVs and c = 3 × 10⁸ ms^–1)

• ≈ 6 × 10⁵ ms^–1

• ≈ 0.6 × 10⁶ ms^–1

• ≈61 × 10³ ms^–1

• ≈61 × 10³ ms^–1

In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with the same λ and D) the separation between the slits needs to be changed to

• 1.8 mm

• 19 mm

• 1.7 mm

• 2.1 mm

When the light of frequency 2v₀ (where v₀ is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is v₁. When the frequency of the incident radiation is increased to 5v₀, the maximum velocity of electrons emitted from the same plate is v₂. The ratio of v₁ to v₂ is

• 1:2

• 1:4

• 2:1

• 4:1