Most Asked Questions
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Dual Nature Of Radiation And Matter

- Get to know usually which areas are frequently asked in the CBSE exam
1

Energy and momentum of photoelectrons

Energy:

Momentum:


A particle having a de Broglie wavelength of 1.0  is associated with a momentum of (given Js)
A
m/s
B
m/s
C
m/s
D
m/s
2

Einstein's photoelectric equation

Einstein's photoelectric equation :

The kinetic energy of the photoelectron coming out may be anything between zero and where is the energy supplied to the individual electrons.


When a metallic surface is illuminate with radiation of wavelength , the stopping potential is V. If the same surface is illuminated with radiation of wavelength , the stopping potential is . The threshold wavelength for the metallic surface is:
A
B
C
D
3

Stopping potential

The smallest magnitude of the anode potential which just stops the photocurrent is called the stopping potential.
This potential should stop even the ost energitic photoelectron. Hence 
Tha value of maximum kinetic energy should be equal to
We know
Photons with energy are incident on a cathode in a photoelectric cell. The maximum energy of emitted photo electrons is . When photons of energy are incident. on , no photoelectrons will reach the anode , if the stopping potential of relative to is :
A
B
C
D
4

Calculate the de broglie wavelength of an electron accelerated by a given potential

Example: An electron of charge e and mass m is accelerated from rest by a potential difference V. Find the de-Broglie wavelength.

Solution:


So de-broglie wavelength



When a metallic surface is illuminate with radiation of wavelength , the stopping potential is V. If the same surface is illuminated with radiation of wavelength , the stopping potential is . The threshold wavelength for the metallic surface is:
A
B
C
D
5

frequency vs potential

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The maximum kinetic energy of the photoelectrons varies linearly with the frequency of incident radiation, but is independent of its intensity.
For a frequency of of incident radiation, lower than the threshold frequency no photoelectric emission is possible even if the intensity is large.
The work function of the surface of a photosensitive material is 6.2 eV. The wavelength of the incident radiation for which the stopping potential is 5 V lies in the :

A
Infrared region
B
X-ray region
C
Ultraviolet region
D
Visible region
6

Maximum velocity of photoelectrons


then
The work function of a metal surface is 1 eV. A light of wavelength 3000 is incident on it. The maximum velocity of the photoelectrons is found as:

The maximum K.E with which electrons comes out,


A photosensitive metallic surface has work function, h . If photons of energy 2h fall on this surface, the electrons come out with a maximum velocity of 4 10 m/s. When the photon energy is increased to 5h, then maximum velocity of photo electrons will be
A
2 10 m/s
B
2 10 m/s
C
8 10 m/s
D
8 10 m/s
7

De-broglie wavelength

De Broglie's wavelength is the wavelength associated with a massive particle,hypothesized by De Broglie that explains Bohr's quantised orbits by bringing in the wave-particle duality.  It is written as
(de broglie wavelength)

An electron is accelerated through a potential difference of 10,000 V. Its de Broglie wavelength is, (nearly) : 
A
B
C
D