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The MCQs below are drawn from the Physics subject category.
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1691
One becquerel is equal to
A. decay of 10 radioactive atoms per second
B. decay of infinity radioactive atoms per second
C. decay of one radioactive atom per second
D. decay of 100 radioactive atoms per second
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Explanation
One becquerel (1 Bq) is defined as one nuclear decay per second.
1692
The γ-rays have
A. continuous tracks
B. thin tracks
C. thick tracks
D. no definite tracks
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Explanation
Gamma rays are uncharged photons and do not produce definite ionization tracks like charged particles.
1693
For same absorbed dose, alpha particles are:
A. 100 times less damaging than X-rays
B. 20 times less damaging than X-rays
C. 20 times more damaging than X-rays
D. 100 times more damaging than X-rays
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Explanation
Alpha particles have a much higher biological effectiveness (RBE) than X-rays; typically their RBE is about 20, so they are ~20 times more damaging for the same absorbed dose.
1694
In the early 20th century, ____ and his team of physicists revolutionised how scientists view the nature of the atom.
A. Ernest Rutherford
B. Radovan
C. Albert Einstein
D. None of these
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Explanation
Ernest Rutherford led experiments revealing the nuclear structure of the atom, fundamentally changing the model of the atom.
1695
In the general formula for spectral series, if we put p = 2, we get the formula for:
A. Lyman series
B. Balmer series
C. Pfund series
D. Paschen series
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Explanation
Putting p=2 in the Rydberg formula yields the Balmer series, which corresponds to transitions terminating at n=2.
1696
When a body is subjected to some external force, deformation is produced in:
A. Length
B. Volume
C. Shape
D. Any of these
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Explanation
An external force can change a body's length, shape, or volume, so deformation may occur in any of these.
1697
(113) The nuclide ""I is radioactive, with a half-life of 8.04 days. At noon, on January 1, the activity of a certain sample is 600 Bq, determine whether the activity at noon on January 24 will be:
A. A little more than 200 Bq
B. A little more than 75 Bq
C. A little less than 75 Bq
D. A little less than 200 Bq
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Explanation
23 days ≈ 2.86 half-lives, so activity = 600*(1/2)^{23/8.04} ≈ 83 Bq, which is a little more than 75 Bq.
1698
An electron of a stationary hydrogen atom passes from the fifth excited state to ground state. What velocity will the atom acquire as a result of photon emission?
A. 6.3 m/sec
B. 2.1 m/sec
C. 8.4 m/sec
D. 4.2 m/sec
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Explanation
Photon carries momentum p = E/c with E from n=6 to n=1 transition; recoil velocity v = p/m_H ≈ 4.2 m/s, matching option B.
1699
The half-life of a radioactive substance depends on
A. pressure
B. no external influences
C. temperature
D. amount of substance
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Explanation
Half-life is an intrinsic property of a radioactive isotope and is independent of external conditions such as pressure or temperature.
1700
Alpha-rays passing through a strong uniform electric field get deflected
A. In the direction of the electric field
B. In the direction perpendicular to both the electric field and direction of motion of rays
C. Do not get deflected at all
D. In the direction opposite to that of the electric field
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Explanation
Alpha particles are positively charged and experience a force in the direction of the electric field vector, so they deflect along the field.
