JEE Physics Dual Nature Of Radiation and Matter MCQs Set B

Question. For an electron microscope, which of the following is false?
(a) Its resolving power is directly proportional to accelerating potential of electrons
(b) It uses magnetic lens to converge electron beam
(c) Its resolving power is inversely proportional to wavelength of electrons
(d) Magnification attained with the help of it is of the order of 10⁶

Answer: A

Question. The approximate wavelength of a photon of energy 2.48 eV is
(a) 5000 Å
(b) 2000 Å
(c) 1000 Å
(d) 500 Å

Answer: A

Question. Wavelength of a 1 keV photon is 1.24 × 10^–9 m. What is the frequency of 1 MeV photon?
(a) 2.4 × 10²⁰ Hz
(b) 1.24 × 10¹⁸ Hz
(c) 2.4 × 10²³ Hz
(d) 1.24 × 10¹⁵ Hz

Answer: A

Question. Which of the following statements is not correct?
(a) Infrared photons have more energy than photons of visible light
(b) Photographic plates are sensitive to infrared rays
(c) Infrared rays are invisible but can cast shadows like visible light
(d) Photographic plates are sensitive to ultraviolet rays

Answer: B

Question. Ultraviolet radiations of 6.2 eV fall on an aluminium surface (work function 4.2 eV). The kinetic energy (in joule) of the fastest electron emitted is approximately
(a) 3.2 × 10^–19
(b) 3.2 × 10^–21
(c) 3.2 × 10^–17
(d) 3.2 × 10^–15

Answer: A

Question. The work function of a metallic surface is 5.01 eV. The photo electrons are emitted when light of wavelength 2000 Å falls on it. The potential difference applied to stop the fastest photo electrons is [h = 4.14 × 10^–15 eV s]
(a) 1.2 volt
(b) 2.24 volt
(c) 3.6 volt
(d) 4.8 volt

Answer: A

Question. A radio transmitter operates at a frequency of 880 kHz and a power of 10 kW. The number of photons emitted per second is
(a) 1.72 × 10³¹
(b) 1.327 × 10³⁴
(c) 13.27 × 10³⁴
(d) 0.075 × 10^–34

Answer: A

Question. Specific heat of water is 4.2 J/g°C. If light of frequency 3 × 10⁹ Hz is used to heat 400 gm of water from 20°C to 40°C, the number of photons needed will be
(a) 1.69 × 10²⁸
(b) 2.80 × 10⁴
(c) 2.80 × 10⁵
(d) 1.69 × 10²⁹

Answer: A

Question. The work function of a certain metal is 2.3 eV. If light of wave number 2 × 10⁶ m^–1 falls on it, the kinetic energies of fastest and slowest ejected electron will be respectively
(a) 0.18 eV, zero
(b) 2.30 eV, 0.18 eV
(c) 0.18 eV, 0.18 eV
(d) 2.48 eV, 0.18 eV

Answer: A

Question. When the electromagnetic radiations of frequencies 4 × 10¹⁵ Hz and 6 × 10¹⁵ Hz fall on the same metal in different experiments, the ratio of maximum kinetic energy of electrons liberated is 1 : 3. The threshold frequency for the metal is
(a) 1 × 10¹⁵ Hz
(b) 2 × 10¹⁵ Hz
(c) 3 × 10¹⁵ Hz
(d) 1.67 × 10¹⁵ Hz

Answer: A

Question. How many photons are emitted by a laser source of 5 × 10^–3 W operating at 632.2 nm in 2 s? (h = 6.63 × 10^–34 Js)
(a) 3.2 × 10^{1.6 × 1016}
(b) 1.6 × 10¹⁶
(c) 4 × 10¹⁶
(d) 0.4 × 10¹⁶

Answer: A

Question. Violet light is falling on a photosensitive material causing ejection of photoelectrons with maximum kinetic energy of 1 eV. Red light falling on metal will cause emission of photoelectrons with maximum kinetic energy (approxim ately) equal to
(a) Zero, that is no photoemission
(b) 0.5 eV
(c) 0.9 eV
(d) 1.2 eV

Answer: A

Question. If frequency of light falling on a photosensitive material doubles
(a) Cut-off voltage becomes more than double
(b) Stopping potential doubles
(c) Saturation photocurrent becomes more than double
(d) Saturation photocurrent doubled

Answer: A

Question. Photoelectrons from metal do not come out with same energy. Most appropriate explanation is
(a) Electrons in metal occupy different energy levels and work function is the minimum energy required for electron in highest level of conduction band to get out of metal
(b) For some electrons, some part of energy gained during inelastic collision with photon is spent in over coming attractive force by nucleus
(c) Work function of a metal is average energy required to pull out electrons
(d) Some electrons loose energy in form of heat

Answer: A

Question. Which one among the following shows particle nature of light?
(a) Photoelectric effect
(b) Refraction
(c) Interference
(d) Polarization

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 : 2
(b) 1 : 4
(c) 1 : 1
(d) 1 : 5

Answer: A

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) 0.5 V
(b) 1.3 V
(c) 1.8 V
(d) 2.3 V

Answer: A

Question. Photoelectric emission occurs only when the incident light has more than a certain minimum
(a) Frequency
(b) Power
(c) Wavelength
(d) Intensity

Answer: A

Question. The threshold frequency for a photosensitive metal is 3.3 × 10¹⁴ Hz. If light of frequency 8.5 × 10¹⁴ Hz is incident on this metal, the cut-off voltage for the photoelectric emission is nearly
(a) 2 V
(b) 1 V
(c) 5 V
(d) 3 V

Answer: A

Question. An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength so emitted illuminates a photosensitive material having work function 2.75 eV. If the stopping potential of the photoelectron is 10 V, then the value of n is
(a) 4
(b) 3
(c) 2
(d) 5

Answer: A

Question. The maximum kinetic energy of the photoelectrons varies
(a) Linearly with the frequency and is independent of the intensity of the incident radiation
(b) Linearly with the frequency and the intensity of the incident radiation
(c) Inversely with the frequency and is independent of the intensity of the incident radiation
(d) Inversely with the intensity and is independent of the frequency of the incident radiation

Answer: A

Question. The work function for Al, K and Pt is 4.28 eV, 2.30 eV and 5.65 eV respectively. Their respective threshold frequencies would be
(a) Pt > Al > K
(b) Al > Pt > K
(c) K > Al > Pt
(d) Al > K > Pt

Answer: A

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) Ultraviolet region
(b) Visible region
(c) Infrared region
(d) X-ray region

Answer: A

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

Answer: A

Question. Light of wavelength 5000 Å falls on a sensitive plate with photoelectric work function of 1.9 eV. The kinetic energy of the photoelectron emitted will be
(a) 0.58 eV
(b) 1.16 eV
(c) 2.48 eV
(d) 1.24 eV

Answer: A

Question. The photoelectric work function for a metal surface is 4.125 eV. The cut-off wavelength for this surface is about
(a) 3000 Å
(b) 2062.5 Å
(c) 6000 Å
(d) 4125 Å

Answer: A