MHT-CET Physics Crash Course Bohr’s Postulates Class 12

“Bohr’s Postulates” MHT-CET Class 12 Physics Crash Course| Chapter Structure of atoms and Nuclei

In this session G.S. Khairnar will discuss the theory and MCQ’s of Bohr’s postulates. The session will be useful for all the aspirants of MHT-CET 2022. The session will be in Marathi and English.

Points to recall:

According to Rutherford’s atomic model

1. Atom has central core called as nucleus.
2. About 99.99% of mass of atom is concentrated in nucleus
3. Major part of an atom has empty space
4. Negatively charged electrons are revolving around the nucleus in circular motion.

But some point in classical electromagnetic theory e.g. accelerated charged particle radiates the energy but it was not observed, so that the stability of Rutherford’s model has restrictions. To reduce drawback Sir Neil Bohr proposed new atomic model.

Bohr’s postulates in detail:

Sir Neil Bohr studied the hydrogen atom and describes the most modern structure of atom in his postulates. He suggested that the negatively charged electron revolves around the positively charged nucleus in circular orbit due to presence of electrostatic force of attraction between the positively charged nucleus and negatively charged electrons.

Postulate-3

An electron radiates photon energy when it jumps from higher energy orbit to lower energy orbit or absorbs energy during transition from lower energy orbit to higher energy orbit. The energy radiated/absorbed is equal to the difference between the energies of the electron in two orbits.

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Bohr’s Postulates MCQ’s:-

Let’s try to solve the following MCQ’s based on Bohr’s postulates….!

Q.1) The centripetal force required for motion of electron around nucleus is provided by…..

1. a) Gravitational force
2. b) Electrostatic force
3. c) Nuclear force
4. d) Weak Nuclear force

Answer

1. b) Electrostatic force

Q.2)  According to Bohr’s atomic model, the angular momentum of electron in a given orbit should be multiple of………..

Q.3) During transition of electrons from orbits of higher energy to the orbit of lower energy, energy is…….

1. a) absorbed
2. b) radiated
3. c) either ‘a’ or b’
4. d) none of these.

Answer

1. c) either ‘a’ or b’

Q.4) The radius of Bohr’s orbit is……..

1. a) directly proportional to principal quantum number
2. b) directly proportional to square of principal quantum number
3. a) inversely proportional to principal quantum number
4. d) inversely proportional to square of principal quantum number

Answer

1. b) directly proportional to square of principal quantum number

Q.5) The difference in angular momentum of revolving electron in 3rd to that of 6th orbit is…..

Q.6) Ratio of radius of 4th Bohr’s orbit to 7th orbit is….

1. a) 4:7
2. b) 7:4
3. c) 16:49
4. d) 49:16

Answer

1. c) 16:49

Q.7) If frequency required for transition of electron from 2nd orbit to 5th orbit is 4×10¹⁵ Hz, the energy absorbed during the transition is…..

Q.8) Which among the following is not correct for electron in Bohr’s orbit?

1. a) Electrostatic force between nucleus and electron provides necessary centripetal force
2. b) Angular momentum of electron is an integral multiple of h/2π
3. c) Energy is absorbed during transition of electron from higher to lower orbit.
4. d) Radius of Bohr’s orbit is directly proportional to square of principal quantum number.

Answer: c) Energy is absorbed during transition of electron from higher to lower orbit.

Q.9) Which amongst the following law is taken as basis for Bohr’s theory

1. a) Law of conservation of linear momentum
2. b) Law of conservation of angular momentum
3. c) Law of conservation of mass
4. c) Law of conservation of Energy

Answer: b) Law of conservation of angular momentum

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