NCERT Solutions for class 12 Physics | Chapter 13 - Nuclei

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Questions
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
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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 88Ra226, 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 class 12 physics chapter 13 nucleiK 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 class 12 physics chapter 13 nuclei 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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