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

Question. A particle is dropped from a height H. The de Broglie wavelength of the particle as a function of height is proportional to
(a) H
(b) H^1/2
(c) H⁰
(d) H ^–1/2

Answer: D

Question. The wavelength of a photon needed to remove a proton from a nucleus which is bound to the nucleus with 1 MeV energy is nearly
(a) 1.2 nm
(b) 1.2 × 10^–3 nm
(c) 1.2 × 10^–6 nm
(d) 1.2 × 10¹ nm

Answer: B

Question. Consider a beam of electrons (each electron with energy E₀) incident on a metal surface kept in an evacuated chamber. Then
(a) no electrons will be emitted as only photons can emit electrons.
(b) electrons can be emitted but all with an energy, E₀.
(c) electrons can be emitted with any energy, with a maximum of E₀ –Φf (Φ is the work function).
(d) electrons can be emitted with any energy, with a maximum of E₀.

Answer: D

Question. The threshold wavelength for photoelectric emission from a material is 5200 Å. Photoelectrons will be emitted when this material is illuminated with monochromatic radiation from a:
(a) 50 watt infrared lamp
(b) 1000 watt infrared lamp
(c) 1 watt ultraviolet lamp
(d) 1 watt infrared lamp

Answer: C

Question. A photoelectric cell is illuminated by a point source of light 1 m away. The plate emits electrons having stopping potential V. Then:
(a) V decreases as distance increase
(b) V increases as distance increase
(c) V is independent of distance (r)
(d) V becomes zero when distance increases or decreases

Answer: C

Question. In a photoelectric experiment, the stopping- potential for the incident light of wavelength 4000 Å is 2 volt. If the wavelength be changed to 3000 Å, the stopping-potential will be:
(a) 2 volt
(b) less than 2 volt
(c) zero
(d) more than 2 volt.

Answer: D

Question. The work-function for a metal is 3 eV. To emit a photoelectron of energy 2 eV from the surface of this metal, the wavelength of the incident light should be:
(a) 6187 Å
(b) 4125 Å
(c) 12375 Å
(d) 2486 Å

Answer: D

Question. In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by
(a) increasing the potential difference between the anode and filament
(b) increasing the filament current
(c) decreasing the filament current
(d) decreasing the potential difference between the anode and filament

Answer: A

Question. The work-function of a surface of a photosensitive material is 6.2 eV. The wavelength of incident radiation for which the stopping potential is 5 V lies in:
(a) ultraviolet region
(b) visible region
(c) infrared region
(d) X-ray region

Answer: A

Question. A proton, a neutron, an electron and an a-particle have same energy. Then their de Broglie wavelengths compare as
(a) λ_p - λ_n > λ_e > λ_a
(b) λ_a < λ_p = λ_n > λ_e
(c) λ_e < λ_p = λ_n > λ_a
(d) λ_e = λ_p = λ_n = λ_a

Answer: B

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

Answer: B

Question. Relativistic corrections become necessary when the expression for the kinetic energy (1/2)mv² , becomes comparable with mc², where m is the mass of the particle. At what de Broglie wavelength will relativistic corrections become important for an electron?
(a) λ = 10 nm
(b) λ = 10^–1 nm
(c) λ = 10^–4 nm
(d) λ = 10^–6 nm

Answer: C, D

Question. Monochromatic light of wavelength 667 nm is produced by a helium neon laser. The power emitted is 9 mW. The number of photons arriving per second on the average at a target irradiated by this beam is:
(a) 3 × 10¹⁶
(b) 9 × 10¹⁵
(c) 3 × 10¹⁹
(d) 9 × 10¹⁷

Answer: A

Question. 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
(a) increase by 2 times
(b) decrease by 2 times
(c) decrease by 4 times
(d) increase by 4 times

Answer: B

Question. Two particles A₁ and A₂ of masses m₁, m₂ (m1 > m₂) have the same de Broglie wavelength. Then
(a) their momenta are the same
(b) their energies are the same
(c) energy of A₁ is less than the energy of A₂
(d) energy of A₁ is more than the energy of A₂

Answer: A, C

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

Answer: B

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

Answer: A

Fill in the Blanks

Question. The minimum energy required by a free electron to just escape from the metal surface is called as ________.
Answer: work function

Question. The maximum kinetic energy of emitted photoelectrons depends on the ________ of incident radiation and the nature of material.
Answer: frequency

Question. The velocity of photon in different media is ________.
Answer: different

Question. The main aim of Davisson-Germer experiment is to verify the ________ nature of moving electrons.
Answer: wave

Question. The minimum frequency required to eject an electron from the surface of a metal surface is called ________ frequency.
Answer: threshold

Question. In photoelectric effect, saturation current is not affected on decreasing the ________ of incident radiation provided its intensity remains unchanged.
Answer: wavelength/frequency

Question. The intensity of radiation also depends upon the number of ________.
Answer: photons

Question. Momentum of photon in different media is ________.
Answer: different

Question. Davisson and Germer experiment established the ________.
Answer: wave nature

Question. Matter wave are associated with ________ particle.
Answer: moving