An electron of mass m and charge e initially at rest gets accelerated by a constant electric field E. The rate of change of de-B roglie wavelength of this electron at time t ignoring relativistic effects is

\(\frac{-h}{eEt^{2}}\)
\(\frac{-eht}{E}\)
\(\frac{-mh}{eEt^{2}}\)
\(\frac{-h}{eE}\)

Solution

In a photoelectric effect measurement, the stopping potential for a given metal is found to be V₀ volt when radiation of wavelength λ₀ is used. If radiation of wavelength 2 λ₀ is used with the same metal then the stopping potential (in volt) will be

\(\frac{V_{0}}{2}\)
2 V₀
\(V_{0}+\frac{hc}{2e\lambda _{0}}\)
\(V_{0}-\frac{hc}{2e\lambda _{0}}\)

Solution

A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 2 m away, the number of electrons emitted by photocathode are reduced by a factor of

1/8
1/16
1/2
1/4

Solution

Intensity α1/(distance)²; No. of photoelectrons emitted is proportional to intensity of incident light.

Radiations of two photon’s energy,twice and ten times the work function of metal are incident on the metal surface successsively. The ratio of maximum velocities of photoelectrons emitted in two cases is

1 : 2
1 : 3
1 : 4
1 : 1

Solution

A parallel beam of light is incident normally on a plane surface absorbing 40% of the light and reflecting the rest. If the incident beam carries 60 watt of power, the force exerted by it on the surface is

3.2 × 10^–8 N
3.2 × 10^–7 N
5.12 × 10^–7 N
5.12 × 10^–8 N

Solution

An ionisation chamber, with parallel conducting plates as anode and cathodes has singly charged positive ions percm³. The electrons are moving toward the anode with velocity 0.4 m/s. The current density from anode to cathode is X 10⁴ m A/m². The velocity of positive ions moving towards cathode is

0.1 m/s
0.4 m/s
zero
1.6 m/s

Solution

The de-Broglie wave length of a proton (mass = 1.6 × 10^–27kg) accelerated through a potential difference of 1 kV is

600 A
0.9 × 10^-12m
7 Å
0.9 nm

Solution

A and B are two metals with threshold frequencies 1.8 × 10¹⁴Hz and 2.2 × 10¹⁴Hz.Two identical photons of energy 0.825 eV each are incident on them. Then photoelectrons are emitted in (Take h = 6.6 × 10^–34Js)

B alone
A alone
neither A nor B
both A and B.

Solution

A light having wavelength 300 nm fall on a metal surface.The work function of metal is 2.54 eV,what is stopping potential ?

2.3 V
2.59 V
1.59 V
1.29 V

If E₁, E₂, E₃ are the respective kinetic energies of an electron,an alpha-particle and a proton, each having the same de-B roglie wavelength, then

E₁ > E₃ > E₂
E₂ > E₃ > E₁
E₁ > E₂ > E₃
E₁ = E₂ = E₃

Solution

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