Physics Questions and Answers – DE Broglie’s Explanation of Bohr’s Second Postulate of Quantisation

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This set of Physics Problems for Class 12 focuses on “DE Broglie’s Explanation of Bohr’s Second Postulate of Quantisation”.

1. Identify the expression for Bohr’s second postulate.
a) L = \(\frac {nh}{2p}\)
b) L = \(\frac {2p}{nh}\)
c) L = nh*2p
d) L = \(\frac {n}{2p}\)
View Answer

Answer: a
Explanation: According to Bohr’s second postulate, an electron revolves around the nucleus of an atom in orbits and, therefore, the angular momentum of the revolution is an integral multiple of \(\frac {h}{2p}\), where h is the Planck’s constant. Thus, the expression for angular momentum is given as:
L = \(\frac {nh}{2p}\)
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2. How did de – Broglie modify Bohr’s postulate?
a) de – Broglie suggested to not take angular momentum into consideration
b) de – Broglie suggested introducing an electric field near the atom
c) de – Broglie suggested that electrons behaved like a wave
d) de – Broglie did not modify Bohr’s second postulate
View Answer

Answer: c
Explanation: de – Broglie hypothesis did modify Bohr’s second postulate. This postulate of Bohr regarding the quantization of the angular momentum of an electron was further explained by Louis de Broglie. According to de – Broglie, a moving electron in its circular orbit behaves like a particle-wave.

3. Which of the following can be chosen to analogously represent the behavior of a particle?
a) Metal rod
b) String
c) Elastic rubber
d) Glass rod
View Answer

Answer: b
Explanation: A string is used to represent the behavior of a particle analogously to the waves traveling on it. Particle waves can lead to standing waves held under resonant conditions. When a stationary string is plucked, it causes several wavelengths to be excited. But, we know that only the ones which have nodes at the ends will survive.
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4. Distance and wavelengths are proportional in a string when referring to the behavior of a particle.
a) True
b) False
View Answer

Answer: a
Explanation: Yes, this is a true statement. In a string, standing waves are formed only when the total distance traveled by a wave is an integral number of wavelengths. In this way, distance and wavelength are proportional to each other. Hence, the expression is given as:
2πrk = kλ

5. How did de – Broglie conclude the modification of Bohr’s II postulate?
a) de – Broglie concluded that electrons cannot be quantized
b) de – Broglie concluded that the wavelength of electrons should be reduced
c) de – Broglie concluded that angular momentum cannot be quantized
d) de – Broglie concluded that wavelengths of matter waves can be quantized
View Answer

Answer: d
Explanation: de – Broglie concluded his modification of Bohr’s second postulate by stating that the wavelengths of matter waves can be quantized. This implies that the electrons can exist in those orbits which had a complete set of several wavelengths.
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