A 200W sodium street lamp emits yellow light of wavelength Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is
(1)
(2)
(3)
(4)
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:
(1)
(2)
(3)
(4)
An \(\alpha -\) particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of \(0.25 \mathrm{~Wb} / \mathrm{m}^2\). The de-Broglie wavelength associated with the particle will be:
1. | \(1~\mathring {\text{A}}\) | 2. | \(0.1~\mathring {\text{A}}\) |
3. | \(10~\mathring {\text{A}}\) | 4. | \(0.01~\mathring {\text{A}}\) |
In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by
1. increasing the filament current
2. decreasing the filament current
3. decreasing the potential difference between the anode and filament
4. increasing the potential difference between the anode and filament
A radioactive nucleus of mass M emits a photon
of frequency and the nucleus recoils. The recoil
energy will be:
(1)
(2) zero
(3) h
(4)
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) 1.2 V
(2) 0.5 V
(3)2.3 V
(4) 1.8 V
Light of two different frequencies whose
photons have energies 1 eV and 2.5 eV
respectively illuminate a metallic surface
whose function is 0.5 eV successively.
Ratio of maximum speeds of emitted
electrons will be
(1) 1:2
(2) 1:1
(3) 1:5
(4) 1:4
Photoelectric emission occurs only when the incident light has more than a certain minimum
1. wavelength
2. intensity
3. frequency
4. power
Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV then the de-Broglie wavelength associated with the electrons would
1. decrease by 2 times
2. decrease by 4 times
3. increase by 4 times
4. increase by 2 times
The threshold frequency for a photo-sensitive metal is If the light of frequency is incident on this metal, the cut-off voltage for the photo-electric emission is nearly:
1. 2 V 2. 3 V
3. 5 V 4. 1 V