CBSE Class 12 Physics Dual Nature Of Matter And Radiation Worksheet Set A

Important Questions for NCERT Class 12 Physics Dual Nature Of Matter And Radiation 

Question. X-ray will not show the phenomenon of :  
(a) interference
(b) deflection by electric field
(c) diffraction
(d) superposition

Answer : B

Question. Which one of the following is not dependent on the intensity of incident photon in a photoelectric experiment ?   
(a) work function of the surface
(b) kinetic energy of photo-electron
(c) stopping potential
(d) amount of photo-electric current

Answer : B

Question. The kinetic energy of an electron, which is accelerated in the potential difference of 100 V, is :   
(a) 1.6 × 10^–10 J
(b) 1.6 × 10⁸ J
(c) 1.6 × 10^–17 J
(d) 1.6 × 10^–18 J

Answer : C

Question. When cathode rays strike a metal target of high melting point with a very high velocity then which of the following are produced ?   
(a) g-waves
(b) Ultrasonic
(c) X-rays
(d) a-rays

Answer : C

Question. Particle nature and wave nature of electromagnetic waves and electrons can be represented by :   
(a) photoelectricity and electron microscopy
(b) light is refracted and diffracted
(c) X-rays is diffracted, reflected by thick metal sheet
(d) electrons have small mass, deflected by the metal sheet.

Answer : A

Question. The surface of zone material is radiated in turn by waves of l = 350 nm and 540 nm respectively.   
The ratio of the stopping potential in the two cases is 2 : 1. The work function of the material is
(a) 4.20 eV
(b) 0.15 eV 
(c) 2.10 eV
(d) 1.05 eV

Answer : D

Question. Light of wavelength 4000 Åis incident on a metal plate whose work function is 2eV. What is maximum kinetic energy of emitted photoelectron?   
(a) 0.5 eV
(b) 1.1 eV
(c) 2.0 eV
(d) 1.5 eV

Answer : B

Question. A laser beam is used for carrying out surgery because it   
(a) is highly monochromatic
(b) is highly coherent
(c) is highly directional
(d) can be sharply focussed

Answer : D

Question. A proton is about 1840 times heavier than an electron. When it is accelerated by a potential difference of 1 kV, its kinetic energy will be   
(a) 1840 keV
(b) 1/1840 keV
(c) 1keV
(d) 920 V

Answer : C

Question. If an electron and a photon propagate in the form of waves having the same wavelength, it implies that they have the same    
(a) energy
(b) momentum
(c) velocity
(d) angular momentum

Answer : B

Question. Characteristic X-rays are produced due to    
(a) transfer of momentum in collision of electrons with target atoms
(b) transition of electrons from higher to lower electronic orbits of an atom
(c) heating of the target
(d) transfer of energy in collision of electrons with atoms in the target.

Answer : B

Question. A photon of energy 4 eV is incident on a metal surface whose work function is 2eV. The minimum reverse potential to be applied for stopping the emission of electrons is    
(a) 2V
(b) 4V
(c) 6V
(d) 8V

Answer : A

Question. Solid targets of different elements are bombarded by highly energetic electron beams. The frequency (f) of the characteristic X-rays emitted from different targets varies with atomic number Z as   
(a) f μ Z
(b) f μ Z2
(c) f μ Z
(d) f μ Z3/2

Answer : B

Question. Hard X-rays for the study of fractures in bones should have a minimum wavelength of 1011 m.   
The accelerating voltage for electrons in X-ray machine should be 
(a) < 124.2 kV
(b) > 124.2 kV
(c) Between 60 kV and 70 kV
(d) = 100 kV

Answer : A

Question. In photoelectric effect, the electrons are ejected from metals if the incident light has a certain minimum    
(a) Wavelength
(b) Frequency .
(c) Amplitude
(d) Angle of incidence

Answer : B

Question. Define work function for a given metallic surface.
Answer. Work function of a metal is the minimum energy required by an electron to escape from the metal surface.

Question. Define threshold frequency.
Answer. For a given metal there exists a certain minimum frequency of the incident radiation below the emission of photoelectron takes place. This frequency is called threshold frequency.

Question. Define stopping potential.
Answer. It is the minimum retarding potential which should be applied across a photoelectric tube in order to make photoelectric current zero.

Question. If the intensity of the incident radiations on a photosensitive surface is doubled, how does the kinetic energy of emitted electron get affected?
Answer. No change.

Question. How will the photoelectric current changes on decreasing the wavelength of incident radiation for a give photosensitive material?
Answer. It remains same.

Question. Two metals A and B have work function 2ev and 5ev respectively which metal has lower threshold wavelength.
Answer. Metal B (as w0 =hν₀, w₀=h c/λ₀)

Two marks

Question. If the potential difference used to accelerate electrons is doubled, by what factor does the de‐ Broglie wavelength of the electron beam charge?
Answer. 12.27A/√v
It become 1√2 times the initial value. ( λ/= λ√2)

Three marks

Question. State laws of photoelectric emission.
Answer. A) For a given photosensitive material and frequency of incident radiation (above the threshold frequency) the photoelectric current is directly proportional to the intensity of
light. The saturation current is directly proportional to the intensity of incident radiations.
B). For a photosensitive material there exists a certain minimum cut‐off frequency below which no photoelectrons are emitted, however high is the intensity of incident radiation. This frequency is called threshold frequency.
c) Above the threshold frequency, the stopping potential or the maximum kinetic energy of the photoelectron is directly proportional to the frequency of incident radiation, but is independent of its intensity.
D) The photoelectric emission is an instantaneous process. The time lag between the incidences of light radiation and the emission of photoelectrons is very small less than 10^‐9 s.

CASE BASED QUESTIONS:

1. Observations in Photoelectric Effect
1. For each metal there is a characteristic minimum frequency below which photoelectric effect is not observed. This is called threshold frequency.
If frequency of light is less than the threshold frequency, there is no ejection of electrons no matter how long it falls on surface or how high is its intensity.
2. The kinetic Energy of electrons emitted is directly proportional to frequency of striking photons &amp; independent of their intensity.
3. The no. of electrons that are ejected per second from metal surface depends upon intensity of striking radiations and doesn’t depend upon their frequency.
4. If frequency of incident light is more than threshold frequency, then the excess energy is imparted to electrons in the form of kinetic energy. (E − W = ½ mv ²)

Question. Electrons are emitted with zero velocities from metal surface when exposed to radiation of wavelength 6800 Ao. Calculate (ν0 = photon’s frequency &amp; W0 = work function)?
a. 3.21x 10¹² /sec &amp;9.7 x 10 ^-19 J
b. 4,14x 10¹⁴ /sec &amp; 2.92 x 10 ^-19J
c. 7.76 x 10¹⁴ /sec &amp;9.7 x 10 ^-19 J
d. 4.14 x 10 ^-14 /sec &amp; 2.922 x 10 ^-19 J
Answer. B

Question. A proton of wavelength 400 nm strikes metal surface. The electrons are ejected with velocity 5.85 × 10 ⁵ m/s. Calculate min. energy required to remove electron from metal surface. (Mass of electron = 9.1 × 10 -31 kg)
a. 29.43 ×10 ^-20 J
b. 34.50 ×10 ²⁰ J
c. 29.43 ×10 ²⁰ J
d. 34.50 ×10 ^-20 J
Answer. D

Question. Einstein could explain photoelectric effect using Plank’s Quantum theory as follows: -
a. Greater he frequency of incident light, greater the kinetic energy of e –
b. Greater the intensity of light more the no. of electrons ejected.
c. Both are correct
d. Only b is correct
Answer. C

Question. Who discovered the Photoelectric effect?
a. Hertz.
b. Einstein.
c. Max Planck
d. de-Broglie
Answer. A

2. PHOTOELECTRIC EMISSION: The photoelectric emission is possible only if the incident light is in the form of packets of energy, each having a definite value, more than the work function of the metal. This show that light is not of wave nature but of particle nature. It is due to this reason that photoelectric emission was accounted by quantum theory of light

Question. Packet of energy are called
a. Electron
b. Quanta
c. Frequency
d. Neutron
Answer. B

Question. One quantum of radiation is called
a. Meter
b. Meson
c. Photon
d. Quark
Answer. C

Question. Energy associated with each photon
a. Hc
b. Mc
c. Hv
d. mc²
Answer. C

Question. Which of the following waves can produce photoelectric effect?
a. UV radiation
b. Infrared radiation
c. Radio waves
d. Microwaves
Answer. A

Question. Work function of alkali metals is
a. less than zero
b. Just equal to other metals
c. greater than other metals
d. Quite less than other metals
Answer. D

Important Questions for NCERT Class 12 Physics Dual Nature Of Matter And Radiation 

Question. When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is
(a) 0.65 eV
(b) 1.0 eV
(c) 1.3 eV
(d) 1.5 eV 

Answer :  B

Question. For photoelectric emission from certain metal the cutoff frequency is ν. If radiation of frequency 2ν impinges on the metal plate, the maximum possible velocity of the emitted electron will be (m is the electron mass)
(a) √(2hν/m)
(b) 2√(hν/m)
(c) √{hν/(2m)}
(d) √hν/m

Answer :  A

Question. Two radiations of photons energies 1 eV and 2.5 eV, successively illuminate a photosensitive metallic surface of work function 0.5 eV. The ratio of the maximum speeds of the emitted electrons is
(a) 1 : 4
(b) 1 : 2
(c) 1 : 1
(d) 1 : 5

Answer :  B

Question. The threshold frequency for a photosensitive metal is 3.3 × 1014 Hz. If light of frequency 8.2 × 1014 Hz is incident on this metal, the cut-off voltage for the photoelectron emission is nearly
(a) 1 V
(b) 2 V
(c) 3 V
(d) 5 V

Answer :  B

Question. The potential difference that must be applied to stop the fastest photoelectrons emitted by a nickel surface, having work function 5.01 eV, when ultraviolet light of 200 nm falls on it, must be
(a) 2.4 V
(b) –1.2 V
(c) –2.4 V
(d) 1.2 V

Answer :  B

Question. The work function of a 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. 

Answer :  C

Question. When photons of energy hu fall on an aluminium plate (of work function E0), photoelectrons of maximum kinetic energy K are ejected. If the frequency of radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be
(a) K + hu
(b) K + E0
(c) 2K
(d) K 

Answer :  A

Question. The work functions for metals A, B and C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einstein’s equation the metals which will emit photoelectrons for a radiation of wavelength 4100 Å is/are
(a) A only
(b) A and B only
(c) all the three metals
(d) none. 

Answer :  B

Question. A photosensitive metallic surface has work function, hu0. If photons of energy 2hu0 fall on this surface, the electrons come out with a maximum velocity of 4 × 10⁶ m/s. When the photon energy is increased to 5hu0, then maximum velocity of photoelectrons will be
(a) 2 × 107 m/s
(b) 2 × 106 m/s
(c) 8 × 106 m/s
(d) 8 × 105 m/s

Answer :  C

Question. The value of Planck’s constant is
(a) 6.63 × 10–34 J/sec
(b) 6.63 × 10–34 kg m2/sec
(c) 6.63 × 10–34 kg m2
(d) 6.63 × 10–34 J sec

Answer :  D

Question. An electron beam has a kinetic energy equal to 100 eV. Find its wavelength associated with a beam, if mass of electron = 9.1 × 10–31 kg and 1 eV = 1.6 × 10–19 J. (Planck’s constant = 6.6 × 10^–34 Js)
(a) 24.6 Å
(b) 0.12 Å
(c) 1.2 Å
(d) 6.3 Å

Answer :  C

Question. If we consider electrons and photons of same wavelength, then they will have same
(a) momentum
(b) angular momentum
(c) energy
(d) velocity.

Answer :  A

Important Questions for NCERT Class 12 Physics Dual Nature Of Matter And Radiation 

Question. Number of ejected photoelectrons increases with increase
(a) in intensity of light
(b) in wavelength of light
(c) in frequency of light
(d) never. 

Answer :  A

Question. The cathode of a photoelectric cell is changed such that the work function changes from W1 to W2 (W2 > W1). If the current before and after changes are I1 and I2, all other conditions remaining unchanged, then (assuming hu > W2)
(a) I1 = I2
(b) I1 < I2
(c) I1 > I2
(d) I1 < I2 < 2I1 

Answer :  A

Question. Light of frequency 1.5 times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled?
(a) Doubled
(b) Four times
(c) One-fourth
(d) Zero

Answer :  D

Question. The work function of a photosensitive material is 4.0 eV. The longest wavelength of light that can cause photon emission from the substance is (approximately)
(a) 3100 nm
(b) 966 nm
(c) 31 nm
(d) 310 nm

Answer :  D

Question. When the light of frequency 2u0 (where u0 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 5u0, the maximum velocity of electrons emitted from the same plate is v2. The ratio of v1 to v2 is
(a) 1 : 2
(b) 1 : 4
(c) 4 : 1
(d) 2 : 1 

Answer :  A

Question. 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 eV s and c = 3 × 10⁸ m s^–1]
(a) ≈ 0.6 × 10⁶ m s^–1
(b) ≈ 61 × 10³ m s^–1
(c) ≈ 0.3 × 10⁶ m s^–1
(d) ≈ 6 × 10⁵ m s^–1

Answer :  A,D

Question. Photons with energy 5 eV are incident on a cathode C in a photoelectric cell. The maximum energy of emitted photoelectrons is 2 eV. When photons of energy 6 eV are incident on C, no photoelectrons will reach the anode A, if the stopping potential of A relative to C is
(a) +3 V
(b) +4 V
(c) –1 V
(d) –3 V

Answer :  D

Question. When a metallic surface is illuminated with radiation of wavelength l, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2l, the stopping potential is V /4. The threshold wavelength for the metallic surface is
(a) 5/2λ
(b) 3λ
(c) 4λ
(d) 5λ

Answer :  B

Question. A photoelectric surface is illuminated successively by monochromatic light of wavelength l and l/2.
If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is (h = Planck’s constant, c = speed of light)
(a) 2hc/λ
(b) hc/3λ
(c) hc/2λ
(d) hc/λ

Answer :  C

Question. A certain metallic surface is illuminated with monochromatic light of wavelength, λ. The stopping potential for photoelectric current for this light is 3V0. If the same surface is illuminated with light of wavelength 2l, the stopping potential is V0. The threshold wavelength for this surface for photoelectric effect is
(a) λ/4
(b) λ/6
(c) 6λ
(d) 4λ

Answer :  D

Question. If particles are moving with same velocity, then which has maximum de Broglie wavelength?
(a) proton
(b) a-particle
(c) neutron
(d) b-particle 

Answer :  D

Question. Which one among the following shows particle nature of light?
(a) photoelectric effect
(b) interference
(b) refraction
(d) polarization.

Answer :  A

Important Questions for NCERT Class 12 Physics Dual Nature Of Matter And Radiation 

Question. 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
(a) 1.8 V
(b) 1.3 V
(c) 0.5 V
(d) 2.3 V 

Answer :  C

Question. When monochromatic radiation of intensity I falls on a metal surface, the number of photoelectrons and their maximum kinetic energy are N and T respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively
(a) N and 2T
(b) 2N and T
(c) 2N and 2T
(d) N and T

Answer :  B

Question. The number of photo electrons emitted for light of a frequency u (higher than the threshold frequency ν₀) is proportional to
(a) threshold frequency (ν₀₎
(b) intensity of light
(c) frequency of light (ν)
(d) ν – ν₀

Answer :  B

Question. A 5 watt source emits monochromatic light of wavelength 5000 Å. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor of
(a) 8
(b) 16
(c) 2
(d) 4 

Answer :  D

Question. A photocell employs photoelectric effect to convert
(a) change in the frequency of light into a change in the electric current
(b) change in the frequency of light into a change in electric voltage
(c) change in the intensity of illumination into a change in photoelectric current
(d) change in the intensity of illumination into a change in the work function of the photocathode.

Answer :  C

Question. A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then
(a) each emitted electron carries one quarter of theinitial energy
(b) number of electrons emitted is half the initial number
(c) each emitted electron carries half the initial energy
(d) number of electrons emitted is a quarter of the initial number.

Answer :  D

Question. When ultraviolet rays incident on metal plate then photoelectric effect does not occur, it occurs by incidence of
(a) infrared rays
(b) X-rays
(c) radio wave
(d) micro wave. 

Answer :  B

Question. A photo-cell is illuminated by a source of light,which is placed at a distance d from the cell. If the distance become d/2, then number of electrons emitted per second will be
(a) remain same
(b) four times
(c) two times
(d) one-fourth. 

Answer :  B

Question. As the intensity of incident light increases
(a) kinetic energy of emitted photoelectrons increases
(b) photoelectric current decreases
(c) photoelectric current increases
(d) kinetic energy of emitted photoelectrons decreases. 

Answer :  C

Question. Which of the following statement is correct?
(a) The photocurrent increases with intensity of light.
(b) The stopping potential increases with increase of incident light.
(c) The current in photocell increases with increasing frequency.
(d) The photocurrent is proportional to the applied voltage. 

Answer :  A

Question. If the momentum of an electron is changed by P, then the de Broglie wavelength associated with it changes by 0.5%. The initial momentum of electron will be
(a) 200P
(b) 400P
(c) P/200
(d) 100P 

Answer :  A

Question. A particle of mass 1 mg has the same wavelength as an electron moving with a velocity of 3 × 10⁶ m s^–1.The velocity of the particle is
(a) 3 × 10^–31 ms^–1
(b) 2.7 × 10^–21 ms^–1
(c) 2.7 × 10^–18 ms^–1
(d) 9 × 10^–2 ms^–1
(mass of electron = 9.1 × 10^–31 kg) 

Answer :  C