# Physics class 12 chapter 12 Objective Questions

## Atoms Objective Questions

1. The first model of atom in 1898 was proposed by

(a) Ernst Rutherford

(b) Albert Einstein

(c) J.J. Thomson

(d) Niels Bohr

Answer: (c) J.J. Thomson

1. In Geiger-Marsden scattering experiment, the trajectory traced by an a-particle depends on

(a) number of collision

(b) number of scattered a-particles

(c) impact parameter

(d) none of these

Answer: (c) impact parameter

1. In the Geiger-Marsden scattering experiment the number of scattered particles detected are maximum and minimum at the scattering angles respectively at

(a) 0° and 180°

(b) 180° and 0°

(c) 90° and 180°

(d) 45° and 90°

Answer: (a) 0° and 180°

1. In the Geiger-Marsden scattering experiment, is case of head-on collision the impact parameter should be

(a) maximum

(b) minimum

(c) infinite

(d) zero

1. Rutherford’s experiments suggested that the size of the nucleus is about

(a) 10-14 m to 10-12 m

(b) 10-15 m to 10-13 m

(c) 10-15 m to 10-14 m

(d) 10-15 m to 10-12 m

Answer: (c) 10-15 m to 10-14 m

1. Which of the following spectral series falls within the visible range of electromagnetic radiation?

(a) Lyman series

(b) Balmer series

(c) Paschen seriee

(d) Pfund series

Answer: (b) Balmer series

1. The first spectral series was discovered by

(a) Balmer

(b) Lyman

(c) Paschen

(d) Pfund

1. Which of the following postulates of the Bohr model led to the quantization of energy of the hydrogen atom?

(a) The electron goes around the nucleus in circular orbits.

(b) The angular momentum of the electron can only be an integral multiple of h/2π.

(c) The magnitude of the linear momentum of the electron is quantized.

(d) Quantization of energy is itself a postulate of the Bohr model.

Answer: (b) The angular momentum of the electron can only be an integral multiple of h/2π.

1. The Bohr model of atoms

(a) assumes that the angular momentum of elec-trons is quantized.

(b) uses Einstein’s photoelectric equation.

(c) predicts continuous emission spectra for at-oms.

(d) predicts the same emission spectra for all types of atoms.

Answer: (a) assumes that the angular momentum of elec-trons is quantized.

1. The Bohr model of atoms :

(A) assumes that the angular momentum of electrons is quantized

(B) uses Einstein’s photoelectric equation

(C) predicts continuous emission spectra for atoms

(D) predicts the same emission spectra for all types of atoms

Answer: (A) assumes that the angular momentum of electrons is quantized

1. Who explained the splitting of special lines in magnetic field ?

(A) Zeeman

(B) Bohr

(C) Summerfield

(D) Einstein

1. The mass of a neutron is :

(A) 1.00866 u

(B) 1.0866 u

(C) 1.866 u

(D) 0.1866 u

Answer: (A) 1.00866 u

1. Half-life of a substance depends on:

(A) pressure

(B) temperature

(C) density

(D) None of these

Answer: (D) None of these

1. The concept of electron spin was introduced by :

(A) Becquerel

(B) Goudsmit

(C) Millikan

(D) Uhlenbeck and Goudsmith

Answer: (D) Uhlenbeck and Goudsmith

1. β-decay produces :

(A) isobars

(B) isotopes

(C) isotones

(D) All the above

1. Transmutation of nuclei was discovered by :

(A) Rutherford

(B) Becquerel

(C) Pauli

(D) None of these

1. The energy equivalent to mass defect is called :

(A) binding energy

(B) internal energy

(C) external energy

(R) enthalpy

Answer: (A) binding energy

1. The binding energy of He is about :

(A) 28.3 eV

(B) 28.3 Mev

(C) 28.3 J

(D) 2.83 Mev

Answer: (B) 28.3 Mev

1. The binding energy of a deuteron is about :

(A) 2.22 MeV

(B) 2.22 J

(C) 2.22 eV

(D) None of these

Answer: (A) 2.22 MeV

1. Who discovered the positron ?

(B) Bohr

(C) Maxwell

(D) Anderson

1. The mass of proton is about :

(A) 9.11 x 10-31 kg

(B) 9.11 x 10-30 kg .

(C) 1.66 x 10-27 kg

(D) 1 kg

Answer: (C) 1.66 x 10-27 kg

1. Chadwick was awarded the Nobel Prize in Physics in 1935 for his discovery of :

(A) electron

(B) proton

(C) neutron

(D) None of these

1. The half life of a radioactive decay is n times its mean life, n is equal to :

(A) 0.6930

(B) 0.0693

(C) 1 / 0.6930

(D) 0.3070

1. Rutherford is the unit of:

(B) energy

(C) photoelectric current

(D) magnetic field

1. The wavelength of Y -rays is of the order of:

(A) 10-8

(B) 10-5 me

(C) 10-11

(D) 10-22 m

1. Which series of hydrogen spectrum does not lie in infrared region?

(A) Humphreys series

(B) Pfund series

(C) Bracket series

(D) Lyman series

Answer: (D) Lyman series

1. The energy of electron in first Bohr orbit of hydrogen atom is -13.6 eV. What is energy of electron in its 2nd Both-orbit.

(A) – 3.4 eV

(B) – 6.8 eV

(C) – 27.2 eV,

(D) + 3.4 eV

Answer: (A) – 3.4 eV

1. Full wave rectifier uses :

(A) two diodes

(B) three diodes

(C) four diodes

(D) five diodes

Answer: (A) two diodes

1. The atomic number and mass number for a specimen are Z and A respectively. The number of neutrons in the atom will be :

(A) A

(B) Z

(C) A + Z

(D) A-Z