Class 12 Physics Chapter 13 Nuclei MCQs

(1) Radius of 1st Bohr orbit is a0 (= 0.529 Å) What is the radius of 2nd Bohr orbit?

[A] 10^-8

[B] 2a₀

[C] 4a₀

[D] 2√2a₀

Answer: 4a₀

(2) The Bohr model of atom:

[A] assumes that the angular momentum of electron 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: assumes that the angular momentum of electron is quantized

(3) The wavelength of y-rays is of the order of:

[A] 10^-8 m

[B] 10^-5 m

[C] 10^-11 m

[D] 10^-22 m

Answer: 10^-11 m

(4) Chadwick was awarded the Nobel prize in Physics in 1935 for his discovery of:

[A] electron

[B] proton

[C] neutron

[D] None of these

Answer: neutron

(5) Nuclear force is:

[A] strong, short range and charge independent force

[B] charge independent, attractive and long range force

[C] strong, charge dependent and short range attractive force

[D] long range, change dependent and attractive force

Answer: strong, short range and charge independent force

(6) Fusion takes place at high temperature because:

[A] Atom are ionised at high temperature

[B] Molecules break up at high temperature

[C] Nuclei break up at high temp.

[D] Kinetic energy is high enough to overcome repulsion between nuclei

Answer: Kinetic energy is high enough to overcome repulsion between nuclei

(7) The ground state energy of Hydrogen atom is -13.6 eV. What is the potential energy of electron in this state?

[A] 0 eV

[B] -13.6 eV

[C] 2 eV

[D] -27.2 eV

Answer: -27.2 eV

(8) The density of a nucleus is of the order of:

[A] 10¹⁵ kg m^-3

[B] 10¹⁸ kg m^-3

[C] 10¹⁷ kg m^-3

[D] 10¹⁶ kg m^-3

Answer: 10¹⁷ kg m^-3

(9) If radio active nuclei emits β-particle, then mass-number:

[A] increased by 1 unit

[B] decreases by 1 unit

[C] increases by 2 unit

[D] decreases by 2 unit

Answer: increased by 1 unit

(10) 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

Answer: 0.6930

(11) An alpha particle is emitted from 88^{Ra²²⁶, then the product nuclei has:}

[A] Z = 84, A = 224

[B] Z = 86, A = 224

[C] Z = 86, A = 222

[D] Z = 82, A = 222

Answer: Z = 86, A = 222

(12) What percentage of radioactive substance is left after 5 half lives?

[A] 3.125%

[B] 6.25%

[C] 12.33%

[D] 31%

Answer: 3.125%

(13)

K radioactive radiations are emitted in the sequence

[A] α, β, γ

[B] β, α, γ

[C] γ, α, β

[D] β, γ, α

Answer: β, α, γ

(14) X-ray was discovered by :

[A] Becqueral

[B] Marie curie

[C] Roengton

[D] Vanlaw

Answer: Roengton

(15) The more readily fissionable isotope of uranium has an atomic mass of:

[A] 234

[B] 235

[C] 236

[D] 238

Answer: 235

(16) The phenomena of radioactivity is:

[A] Exothermic change with increase or decrease with temperature

[B] increases on applied pressure

[C] nuclear process does not depend on external factors

[D] None of these

Answer: nuclear process does not depend on external factors

(17) When one gm of mass is converted into energy, it is equal to:

[A] 10³ kWh

[B] 10⁹ kWh

[C] 10¹⁰ kWh

[D] 10¹¹ kWh

Answer: 10³ kWh

(18) The mass no. of a nucleus is M and its atomic no. is Z. The number of neutrons in the nucleus is :

[A] M – Z

[B] M

[C] Z

[D] M + Z

Answer: M – Z

(19) How many electrons are contained in U nucleus?

[A] 92

[B] 146

[C] 238

[D] 0

Answer: 0

(20) The order of nuclear density is :

[A] 10³

[B] 10¹⁷

[C] 10⁶

[D] None

Answer: 10¹⁷

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