CBSE Class 12 Physics Dual Nature Nucleus and Atom Assignment

TEST SERIES (PHYSICS)

DUAL NATURE,NUCLEUS AND ATOM 

Question. An electron of mass m and charge e initially at rest gets accelerated by a constant electric field E. The rate of change of de-Broglie wavelength of this electron at time t ignoring relativistic effects is
(a) -h/eEt²
(b) -eht/E
(c) -mh/eEt²
(d) -h/eE

Answer: A

Question. Radiations of intensity 0.5 W/m² are striking a metal plate.
The pressure on the plate is
(a) 0.166 × 10^–8 N/m²
(b) 0.332 × 10^–8 N/m²
(c) 0.111 × 10^–8 N/m²
(d) 0.083 × 10^–8 N/m²

Answer: A

Question. The magnitude of the de-Broglie wavelength (l) of electron (e), proton (p), neutron (n) and a-particle (a) all having the same energy of 1 MeV, in the increasing order will follow the sequence
(a) λ_e, λ_p, λ_n, λ_α
(b) λ_e, λ_n, λ_p, λ_α
(c) λ_α, λ_n, λ_p, λ_e
(d) λ_p, λ_e, λ_α, λn 

Answer: C

Question. Light from a hydrogen discharge tube is incident on the cathode of a photoelectric cell, the work function of the cathode surface is 4.2 eV. In order to reduce the photocurrent to zero the voltage of the anode relative to the cathode must be made
(a) – 4.2 V
(b) – 9.4 V
(c) – 17.8 V
(d) + 9.4 V

Answer: B

Question. Einstein’s work on photoelectric effect provided support for the equation
(a) E = hn
(b) E = mc²
(c) E = -Rhc/n²
(d) K.E. = 1/2 mv2

Answer: A

Question. The glancing angle in a X-ray diffraction is 30º and the wavelength of X-rays used is 20 nm. The interplanar spacing of the crystal dffracting these X-rays will be
(a) 40 nm
(b) 20 nm
(c) 15 nm
(d) 10 nm

Answer: B

Question. The maximum velocity of an electron emitted by light of wavelength λ incident on the surface of a metal of work function Φ is 

Answer: C

Question. The maximum distance between interatomic lattice planes is 15 Å. The maximum wavelength of X-rays which are diffracted by this crystal will be
(a) 15 Å
(b) 20 Å
(c) 30 Å
(d) 45 Å

Answer: C

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

Answer: D

Question. If the X-ray tube is working at 20 kV then the minimum wavelength of X-rays will be
(a) 0.31 Å
(b) 0.62 Å
(c) 0.93 Å
(d) 0.47 Å

Answer: B

Question. A radio transmitter operates at a freqency 880 kHz and a power of 10 kW. The number of photons emitted per second is
(a) 1.72 × 10³¹
(b) 1.327 × 10²⁵
(c) 1.327 × 10³⁷
(d) 1.327 × 10⁴⁵

Answer: A

Question. For photoelectric emission from certain metal the cut-off frequency is n. If radiation of frequency 2n impinges on the metal plate, the maximum possible velocity of the emitted electron will be (m is the electron mass) 
(a) √hn / m
(b) √2hn / m
(c) √2 hn / m
(d) √hn / (2m)

Answer: B

Question. The momentum of a photon of an electromagnetic radiation is 3.3 × 10^–29 kgms^–1. What is the frequency of the associated waves ?
[h = 6.6 × 10^–34 Js; c = 3 × 10⁸ ms^–1)
(a) 1.5 × 10¹³ Hz
(b) 7.5 × 10¹² Hz
(c) 6.0 × 10³ Hz
(d) 3.0 × 10³ Hz

Answer: A

Question. An electron is moving with an initial velocity v = v₀ î and is in a magnetic field B = B₀ ĵ . Then, it's de-Broglie wavelength 
(a) remains constant
(b) increases with time
(c) decreases with me
(d) increases and decreases periodically

Answer: A

Question. The wavelength of a 1 keV photon is 1.24 × 10^–9 m. What is the frequency of 1 MeV photon ?
(a) 1.24 × 10¹⁵
(b) 2.4 × 10²⁰
(c) 1.24 × 10¹⁸
(d) 2 × 4 × 10²³

Answer: B

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) 1.2 V
(c) 0.5 V
(d) 2.3 V

Answer: C

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_α
(b) λ_α < λ_p = λ_n > λ_e
(c) λ_e < λ_p = λ_n > λ_α
(d) λ_e = λ_p = λ_n = λα

Answer: B

Question. The frequency and work function of an incident photon are v and Φ0. If v₀ is the threshold frequency then necessary condition for the emission of photoelectron is
(a) v < v₀
(b) v = v₀/2
(c) v ≥ v₀
(d) None of these

Answer: C

Question. The wavelength le of an electron and lp of a photon are of same energy E are related by
(a) λ_p ∝ λ_e
(b) λ_p ∝ √λ_e
(c) λ_p ∝ 1/√λ_e
(d) λ_p ∝ λe²

Answer: D

Question. A source of light is placed at a distance of 50 cm from a photocell and the stopping potential is found to be V₀. If the distance between the light source and photocell is made 25 cm, the new stopping potential will be
(a) 2V₀
(b) V₀/2 
(c) V₀
(d) 4V0

Answer: C

Question. The wavelength of a photon needed to remove a proton from a nucleus which is bound to the nuclear 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 × 10 nm

Answer: B

Question. The quantity e²/2hε₀c has a value
(a) 1/137 ms^-1
(b) 2/137 ms^-1
(c) 1/137
(d) 2/137

Answer: C

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 photoelectric emission is nearly
(a) 2 V
(b) 3 V
(c) 5 V
(d) 1 V

Answer: A

Question. The de-Broglie wavelength of neutron in thermal equilibrium at temperature T is
(a) 30.8/√T Å
(b) 3.08/√T Å
(c) 0.308/√T Å
(d) 0.0308/√T Å

Answer: A

Question. When the energy of the incident radiation is incredased 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. If the kinetic energy of the particle is increased to 16 times its previous value, the percentage change in the de-Broglie wavelength of the particle is : 
(a) 25
(b) 75
(c) 60
(d) 50

Answer: B

Question. Light of wavelength 500 nm is incident on a metal with work function 2.28 eV. The de Broglie wavelength of the emitted electron is: 
(a) < 2.8 × 10^-9 m
(b) ≥. 2.8 × 10^-9 m
(c) ≤ 2.8 × 10^-12 m
(d) < 2.8 × 10^-10 m

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 – Φ (Φ is the work function)
(d) electrons can be emitted with any energy, with a maximum of E0

Answer: D

Question. Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the materials is
(a) 4 × 10¹⁵ Hz
(b) 5 × 10¹⁵ Hz
(c) 1.6 × 10¹⁵ Hz
(d) 2.5 × 10¹⁵ Hz

Answer: C

Question. Consider figure given below. Suppose the voltage applied to A is increased. The diffracted beam will have the maximum at value of θ that 

(a) will be larger than the earlier value
(b) will be the same as the earlier value
(c) will be less than the earlier value
(d) will depend on the target

Answer: C
 

Q1.A proton and an alpha particle both initially at rest are accelerated so as to have the same kinetic energy. What is the ratio of their De Broglie wave length.

Q2.Maximum velocity of electron emitted from a metal of negligible work function is v when a radiation of frequency f falls on it. what would be the velocity of electrons when a radiation of frequency 4f falls on same metal surface.

Q3.Find the ratio of densities of two nuclii of which mass number are 27 and 64.

Q4.Calculate the half life of a radioactive substance of which the activity drops to 1/16th of its initial value in 30 years.

Q5.For which transition shortest wavelength of Balmer series belongs?

Q6. Write the points which indicates that photo electric effect proves to particle nature of light.

Q7.A radiation of wavelength λ falls on a metal surface of negligible work function. Find the deBroglie wavelength associated with emitted electrons.

Q8. Draw a graph showing the variation of potential energy between a pair of nucleons as a function of their separation. Indicate the regions in which the nuclear force is (i) attractive(ii) repulsive

Q9.Why is the mass of a nucleus always less than the sum of masses of its constituents, neutrons and protons. If the total number of neutrons and protons in a nuclear reaction is conserved, how then the energy absorbed or evolved in the reaction?

Q10.By using the concept of deBroglie wavelength prove the Bohrs condition of quantization condition of angular momentum of an electron in an orbit.

Please refer to the link below for CBSE Class 12 Physics Dual Nature Nucleus and Atom Assignment