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1901
Find the correct statement about Bohr atom model.
A. The centripetal force on the electron is incorrectly rendered in OCR
B. Electrostatic force of attraction between the nucleus and the electron is incorrectly rendered in OCR
C. Bohr used the Planck's constant to explain his two postulates
D. It could not explain about the spectral lines of hydrogen atoms
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Explanation
Bohr's model explicitly used Planck's constant in quantization of angular momentum and energies.
1902
Each atom in a metal crystal vibrates about a fixed point with an amplitude that:
A. Decreases with rise in temperature
B. Is not affected by rise in temperature
C. Increases with rise in temperature
D. Both (B) and (C)
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Explanation
As temperature increases, atomic vibrations increase, so the amplitude of vibration increases with rise in temperature.
1903
Which of the following properties is not exhibited by X-rays?
A. Diffraction
B. Interference
C. Polarization
D. Deflection of electric field
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Explanation
X-rays exhibit interference, diffraction and polarization, but being uncharged they are not deflected by electric fields.
1904
The electrons emitted during beta decay having energies of only:
A. 4 or 5 MeV
B. 8 or 9 MeV
C. 6 or 7 MeV
D. 2 or 3 MeV
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Explanation
The OCR header indicates option B as the answer for this beta-decay energy range question.
1905
Radio active phosphorus decays to silicon according to the reaction; the charge on the particle X is
A. -1
B. +1
C. +2
D. zero
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Explanation
A decay that reduces atomic number by one (P → Si) corresponds to emission of a positron, which has charge +1.
1906
The energy of a quantum states is primarily dependent upon the quantum number:
A. l
B. m
C. n
D. s
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Explanation
The principal quantum number n primarily determines the energy levels of quantum states, per the provided answer key.
1907
Geiger-Miller counter is used to detect
A. Electrons
B. Light
C. Photons
D. Radioactive radiations
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Explanation
A Geiger-Müller counter detects ionizing (radioactive) radiation such as alpha, beta, and gamma particles.
1908
According to the work of Marie Curie, the smoke detector uses
A. Alpha Radiation
B. Beta Radiation
C. Gamma Radiation
D. None of these
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Explanation
Ionization smoke detectors commonly use an alpha-emitting source (e.g., americium-241) as per radioactive source applications.
1909
When a neutron is captured by a proton, it results in the formation of
A. deuterons and x-rays
B. deuteron and a x-ray photon
C. 4 deuterons and 2 γ-ray photons
D. 2 deuterons and 4 γ-ray photons
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Explanation
A proton capturing a neutron forms a deuteron (pn) and typically emits a photon (gamma/x-ray) to conserve energy.
1910
The counting rate observed from a radioactive source at t = 0 s was 1600 counts/s and at t = 8 s it was 100 counts/s. The counting rate observed, in counts/s, at t = 6 s will be
A. 200
B. 300
C. 400
D. 150
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Explanation
From 1600 to 100 in 8 s is a factor 1/16 (three half-lives), so half-life = 2 s; at 6 s (three half-lives from 0? actually 6s = 3 half-lives) activity = 1600*(1/2)^3 = 200 counts/s.