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## Thursday, 28 January 2021

### CBSE Class 12 Physics - MCQ and Online Tests - Unit 13 - Nuclei

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 13 – Nuclei

Every year CBSE conducts board exams for 12th standard. These exams are very competitive to all the students. So our website provides online tests for all the 12th subjects. These tests are also very effective and useful for those who preparing for competitive exams like NEET, JEE, CA etc. It can boost their preparation level and confidence level by attempting these chapter wise online tests.

These online tests are based on latest CBSE Class 12 syllabus. While attempting these our students can identify the weak lessons and continuously practice those lessons for attaining high marks. It also helps to revise the NCERT textbooks thoroughly.

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 13 – Nuclei

Question 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) $$\frac{1}{0.6930}$$
(d) 0.3070

Question 2.
An electron and a positron each having a mass equivalent to 0.53 MeV annihilate each other and produce a photon. The minimum energy of the photon is.
(a) 0.53 MeV
(b) 1.06 MeV
(c) 2.12 MeV
(d) zero

Question 3.
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: (a) increased by 1 unit

Question 4.
Rutherford is the unit of:
(b) energy
(c) photoelectric current
(d) magnetic field

Question 5.
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

Question 6.
How many electrons are contained in $$_{92}^{238}$$U nucleus?
(a) 92
(b) 146
(c) 238
(d) 0

Question 7.
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

Question 8.
According to Yukawa’s theory of nuclear forces, the origin of nuclear force between nucleons is due to the exchange of
(a) mesons
(b) photons
(c) electrons
(d) positrons

Question 9.
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

Question 10.
Which of the following atoms has the lowest ionization potential?
(a) $$_{8}^{8}$$O
(b) $$_{7}^{14}$$N
(c) $$_{55}^{133}$$Cs
(d) $$_{18}^{40}$$Ar

Answer: (c) $$_{55}^{133}$$Cs

Question 11.
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: (a) strong, short range and charge independent force

Question 12.
In the given reaction:
$$_{Z}^{A}$$X → $$_{Z+1}^{A}$$ Y → $$_{Z-1}^{A-4}$$ K → $$_{Z-1}^{A-4}$$ K radioactive radiations are emitted in the sequence
(a) α, β, γ
(b) β, α, γ
(c) γ, α, β
(d) β, γ, α

Question 13.
An alpha particle is emitted from $$_{88}$$Ra$$^{226}$$, 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: (c) Z = 86, A = 222

Question 14.
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: (a) assumes that the angular momentum of electron is quantized

Question 15.
X-ray was discovered by :
(a) Becqueral
(b) Marie curie
(c) Roengton
(d) Vanlaw

Question 16.
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: (d) Kinetic energy is high enough to overcome repulsion between nuclei

Question 17.
The order of nuclear density is :
(a) 103
(b) 1017
(c) 106
(d) None

Question 18.
Chadwick was awarded the Nobel prize in Physics in 1935 for his discovery of:
(a) electron
(b) proton
(c) neutron
(d) None of these

Question 19.
The helium atom does not contain
(a) two protons
(b) two electrons
(c) two neutrons
(d) six nucleons

Question 20.
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

Question 21.
The isotope generally used for the treatment of cancer is:
(a) I131
(b) Hg197
(c) O15
(d) Co60

Question 22.
When the mass of a sample of a radioactive substance decreases, the mean life of the sample:
(a) increases
(b) decreases
(c) remain unchanged
(d) first decreases then increases

Question 23.
What percentage of radioactive substance is left after 5 half lives?
(a) 3.125%
(b) 6.25%
(c) 12.33%
(d) 31%

Question 24.
Alpha particle emitted from a radioactive material are:
(a) Helium nuclei
(b) Hydrogen nuclei
(c) Lithium nuclei
(d) None of the above

Question 25.
Mass is converted into energy according to the relation:
(a) E = me²
(b) E = mgh
(c) E = $$\frac{3}{2}$$me²
(d) E = $$\frac{mgH}{c^2}$$