CBSE Class 12 Physics Dual Nature of Radiation and Matter Worksheet Set A

CBSE Class 12 Physics Dual Nature of Radiation and Matter Worksheet Set A

Question. The de-Broglie wavelength of a neutron at 927°C is λ. What will be its wavelength at 27 °C ?
(a) λ/2
(b) λ
(c) 2 λ
(d) 4 λ

Answer: C

Question. Ultraviolet radiation of 6.2 eV falls on an aluminium surface (workfunction 4.2 eV). The kinetic energy in joule of the faster electron emitted is approximately
(a) 3 × 10^–21
(b) 3 × 10^–19
(c) 3 × 10^–17
(d) 3 × 10^–15

Answer: B

Question. A material particle with a rest mass m₀ is moving with speed of light c. The de-Broglie wavelength associated is given by
(a) h/m₀c
(b) m₀c/h
(c) zero
(d) ∞

Answer: C

Question. For a given photosensitive material and frequency (> threshold frequency) of incident radiation, the photoelectric current varies with the intensity of incident light as 

Answer: A

Question. An X-ray tube is operated at 15 kV. Calculate the upper limit of the speed of the electrons striking the target.
(a) 7.26 × 10⁷ m/s
(b) 7.62 × 10⁷ m/s
(c) 7.62 × 10⁷ cm/s
(d) 7.26 × 10⁹ m/s

Answer: A

Question. Which of the following figures represents the variation of particle momentum and the associated de-Broglie wavelength?

Answer: A

Question. The de-Broglie wavelength of an electron moving in the nth Bohr orbit of radius r is given by
(a) 2πr/n
(b) nπr
(c) nr/2π
(d) nr/π

Answer: A

Question. A photon of 1.7 × 10^–13 joule is absorbed by a material under special circumstances. The correct statement is
(a) Electrons of the atom of absorbed material will go the higher energy states
(b) Electron and positron pair will be created
(c) Only positron will be produced
(d) Photoelectric effect will occur and electron will be produced

Answer: B

Question. In a photoelectric effect measurement, the stopping potential for a given metal is found to be V₀ volt when radiation of wavelength l0 is used. If radiation of wavelength 2 λ₀ is used with the same metal then the stopping potential (in volt) will be
(a) V₀/2
(b) 2 V₀
(c) V₀ + hc/2eλ₀
(d) V₀ - hc/2eλ0

Answer: D

Question. If the energy of a photon is 10 eV, then its momentum is
(a) 5.33 × 10^–23 kg m/s
(b) 5.33 × 10^–25 kg m/s
(c) 5.33 × 10^–29 kg m/s
(d) 5.33 × 10^–27 kg m/s

Answer: D

Question. When X-rays of wavelength 0.5 Å would be transmitted by an aluminium tube of thickness 7 mm, its intensity remains one-fourth. The attenuation coefficient of aluminium for these X-rays is
(a) 0.188 mm^–1
(b) 0.189 mm^–1
(c) 0.198 mm^–1
(d) None of these

Answer: C

Question. The work function of aluminium is 4.2 eV. If two photons, each of energy 3.5 eV strike an electron of aluminium, then emission of electrons
(a) will be possible
(b) will not be possible
(c) Data is incomplete
(d) Depends upon the density of the surface

Answer: B

Question. For intensity I of a light of wavelenght 5000Å the photoelectron saturation current is 0.40 μA and stopping potential is 1.36 V, the work function of metal is
(a) 2.47 eV
(b) 1.36 eV
(c) 1.10 eV
(d) 0.43 eV

Answer: C

Question. A source S₁ is producing, 10¹⁵ photons per second of wavelength 5000 Å. Another source S₂ is producing 1.02×10¹⁵ photons per second of wavelength 5100Å Then, (power of S₂) to the (power of S₁) is equal to :
(a) 1.00
(b) 1.02
(c) 1.04
(d) 0.98

Answer: A

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: D

Question. Photoelectric emmision occurs only when the incident light has more than a certain minimum
(a) power
(b) wavelength
(c) intensity
(d) frequency

Answer: D

Question. The kinetic energy of electron (in electron volt) moving with a velocity of 4 × 10⁶ m/s will be
(a) 60 eV
(b) 50 eV
(c) 30 eV
(d) 45.5 eV

Answer: D

Question. If the momentum of 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) 200 P
(b) 400 P
(c) P/200
(d) 100 P

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. An electron (mass m) with an initial velocity v = v₀ î is in an electric field E = -E₀ ĵ . If λ₀ = h /mv, it's de-Broglie wavelnegth at time t is given by

Answer: C 

ONE MARK QUESTIONS:

Question. The graph shows variation of stopping potential V0 versus frequency of incident radiation ν for two photosensitive metals A and B. Which of the two metals has higher threshold frequency and why?
Answer :

Question. Name the phenomenon which shows the quantum nature of electromagnetic radiation.
Answer : Photoelectric effect shows the quantum nature of electromagnetic radiation.

Question. Which experiment establishes the wave nature of the particle?
Answer : The wave nature of the particle is established by Davisson- Germer Experiment.

Question. Which optical phenomenon is exhibited by the particle in famous Davisson – Germer Experiment?
Answer : Diffraction of light.
 

THREE MARKS QUESTIONS

Question. Light of intensity'I' and frequency ‘V’ is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on photo current when
(i) the intensity of light is gradually increased,
(ii) the frequency of incident radiation is increased, and
(iii) the anode potential is increased?
In each case, all other factors remain the same. Explain, giving justification in each case.
Answer :  (i) As we increase the intensity of radiation the number of photons increases. And we know that each photon will impart energy to each electron hence the number of electron increases so that the photo-current.
ii) On increasing the frequency above threshold frequency, only the energy of the photons increases not their numbers. Hence the photo- current will remain almost constant.
(iii) With an increase in the accelerating potential, the photoelectric current increases first, reaches maximum when all the electrons gets collected at the positive potential plate and then remains constant. The maximum value of the anode current is called saturation current.

Question. State two important properties of photon which are used to write Einstein’s photoelectric equation.
Define (i) stopping potential and (ii) threshold frequency, using Einstein’s equation and drawing necessary plot between relevant quantities.
Answer : The properties of photon used to write Einstein’s photoelectric equation are 
(i) The rest mass of the photon is zero.
(ii) The energy of the photon is E = hν.
Stopping potential: For a particular frequency of incident radiation, the minimum negative (retarding) potential V0 for which the photocurrent stops or becomes zero is called the cut-off or stopping potential.
Threshold frequency: The minimum frequency required for photoelectrons to be emitted from a metal surface is called the threshold frequency.
The graph between stopping potential and frequency of incident radiation is shown below: (Image 6)
 

Question. Using photon picture of light, show how Einstein’s photoelectric equation can be established. Write two features of photoelectric effect which cannot be explained by wave theory.
Answer :

Question. Draw graphs showing variation of photoelectric current with applied voltage for two incident radiations of equal frequency and different intensities. Mark the graph for the radiation of higher intensity.
Answer :

              Very Short Answer

Q1)       Who found the charge on an oil droplet?

Q2)       What is work function of the metal?

Q3)       Who discovered the X-rays?

Q4)       Where we will use the unit of energy?

Q5)       Who discovered the cathode rays?

              Short Answer

Q6)       What do you understand by the Einstein’s photoelectric equation?

Q7)       Define electron emission?

Q8)       What do you understand by the Hertz’s observation?

Q9)       What is the Davisson and Germer experiment?

Q10)     What do you mean by the Hallwachs’ and Lenard’s observation?

              Long Answer

Q11)     What are the points we have to take care for the photon picture of the electromagnetic radiation?

Q12)     State the difference between electromagnetic wave and matter wave?

Q13)     Write short note on photocell?

Q14)     State the difference between photoelectric effect and photovoltaic effect?

Q15)     What kind of experimental features of observations we have to take care for photoelectric effect?