NCERT Solutions for class 12 Physics | Chapter 11 - Dual Nature of Radiation and Matter

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Questions
1 K1 and K2 are maximum kinetic energies of photo electrons emitted when light having wavelengths λ1 and λ2 respectively incident on a metallic surface. If λ1 = 3λ2, then
A K1 < (K2/3)
B K1 > (K2/3)
C K1 = 3K2
D None of these

Answer:K1 < (K2/3)
2 When light of wavelength λ strikes a photo sensitive surface, then the kinetic energy of ejected electrons is E. If the kinetic energy is to be changed to 2E then the wavelength should be changed to λ’. The correct relation between λ and λ’ is
A λ’ = λ
B λ’ =2 λ
C λ/2 < λ’< λ
D λ’ = λ/2

Answer:λ/2 < λ’< λ
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3 The velocity of the most energetic electrons emitted from a metallic surface is doubled when the frequency (v) of incident radiation is double. What is the work function of this metal?
A zero
B hv/3
C hv/2
D 2hv/3

Answer:2hv/3
4 In a plot of the kinetic energy of the emitted photo electrons from a metal verses the frequency of the incident radiation gives a straight line whose slope
A depends on the nature of the metal used
B depends on the intensity of the radiation
C is the same for all metals and independent of the intensity of the radiation
D depends both on the intensity of the radiation and the metal used

Answer:is the same for all metals and independent of the intensity of the radiation
5 Which of the following shows particle nature of light?
A Refraction
B Interference
C Polarization
D Photoelectric effect

Answer:Photoelectric effect
6 A photoelectric cell is a device which
A converts light into electricity
B converts electricity into light
C stores light
D stores electricity

Answer:converts light into electricity
7 Photoelectric effect is the phenomenon in which
A photons come out of a metal when it is hit by a beam of electrons.
B photons come out of the nucleus of an atom under the action of an electric field.
C electrons come out of a metal with a constant velocity
D which depends on the frequency and intensity of incident light wave.

Answer:The work function of different metals is different.
8 The minimum energy required to eject an electron, from the metal surface is called
A atomic energy
B mechanical energy
C electrical energy
D work function

Answer:The minimum energy required for the emission of electrons is called work function.
9 In the photoeletric effect, electrons are emitted
A at a rate that is proportional to the amplitude of the incident radiation
B with a maximum velocity proportional to the frequency of the incident radiation
C at a rate that is independent of the emitter
D only if the frequency of the incident radiations is above a certain threshold value

Answer:Photoelectrons are emitted if the frequency of incident light is greater than the threshold frequency.
10 Einstein’s photoelectric equation states that

hν = W0 + Ek.

In this equatin, Ek refers to the

A kinetic energy of all the emitted electrons
B mean kinetic energy of the emitted electrons
C maximum kinetic energy of the emitted electrons
D minimum kinetic energy of the emitted electrons

Answer:In the given relation Ek stands for maximum K.E. of emitted photoelectrons.
11 The maximum energy of electrons released in a photocell is independent of
A the frequency of the incident light
B the intensity of the incident light
C the nature of the cathode
D All of the above

Answer:Max. K.E. of phtoelectrons emitted is independent of intensity of incident light.
12 A photoelectric cell converts
A light energy into heat energy
B light energy to sound energy
C light energy into electric energy
D electric energy into light energy

Answer:Photoelectric cell converts light energy into electric energy.
13 The photo-electrons emitted from a metal surface are such that their velocity
A is zero for all
B is same for all
C lies between zero and infinity
D lies between zero and a finite maximum

Answer:lies between zero and a finite maximum
14 The momentum of a photon of wavelength λ is
A hλ
B h/λ
C λ/h
D h/cλ

Answer:h/λ
15 In a photon-particle collision, the quantity that does not remain conserved is
A total energy
B total momentum
C number of photons
D None of these

Answer:number of photons
16 The photoelectric effect is based on the law of conservation of
A momentum
B energy
C angular momentum
D mass

Answer:energy
17 When light is incident on a metal surface the maximum kinetic energy of emitted electrons
A vary with intensity of light
B vary with frequency of light
C vary with speed of light
D vary irregularly

Answer:vary with frequency of light
18 Photons are deflected by
A electric field only
B magnetic field only
C electromagnetic field
D None of these

Answer:None of these
19 The photoelectric current does not depend upon the

(i) frequency of incident light

(ii) work function of the metal

(iii) stopping potential

(iv) intensity of incident light

A (i) and (iv) only
B (ii) and (iii) only
C (iii) only
D (ii) only

Answer:(iii) only
20 The theory of quantisation of electric charge was given by
A William Crookes
B J. J. Thomson
C R.A. Millikan
D Wilhelm Hallwachs

Answer:R.A. Millikan

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