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1601
M_p denotes the mass of a proton and M_n that of a neutron. A given nucleus, of binding energy B, contains Z protons and N neutrons. The mass M(N,Z) of the nucleus is given by (c is the velocity of light)
A. M(N,Z) = N M_n + Z M_p - B c^2
B. M(N,Z) = N M_n + Z M_p + B/c^2
C. M(N,Z) = N M_n + Z M_p - B/c^2
D. M(N,Z) = N M_n + Z M_p + B c^2
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Correct Option
Explanation
The nuclear mass equals the sum of constituent nucleon masses minus the binding energy divided by c^2, so option A is the correct mass formula.
1602
When 3p subshell is complete, the newly entering electron goes into
A. 4s
B. 4p
C. 2p
D. 3d
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Correct Option
Explanation
Once 3p is filled (3p6), the next electron enters the 4s orbital according to the filling order.
1603
The characteristic X-ray spectrum is due to:
A. The absorption of neutrons by target material
B. The bombardment of target material by electrons
C. The bombardment of target material by protons
D. The bombardment of target material by alpha particles
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Correct Option
Explanation
Characteristic X-rays arise when incident high-energy electrons knock out inner-shell electrons, and outer electrons fill the vacancies producing X-ray photons.
1604
The minimum amount of energy an individual electron has to gain to escape from a particular surface is called
A. kinetic energy
B. wave number
C. work function
D. threshold frequency
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Correct Option
Explanation
The work function is the minimum energy needed for an electron to escape from a material's surface.
1605
The de Broglie wavelength associated with electrons revolving round the nucleus in a hydrogen atom in ground state will be
A. 3.3 Å
B. 0.3 Å
C. 6.62 Å
D. 10 Å
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Correct Option
Explanation
For hydrogen ground state λ = 2πa0 ≈ 2π×0.529 Å ≈ 3.32 Å, so option B (3.3 Å) is correct.
1606
If the operating voltage of an X-ray tube is increased
A. X-rays intensity decreases
B. X-rays intensity increases
C. X-rays wavelength limit on the minimum side decreases
D. X-rays wavelength limit on the maximum side increases
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Correct Option
Explanation
Higher accelerating voltage produces higher energy photons, which reduces the minimum wavelength (shorter λ).
1607
141. When two deuterons are merged to form a helium nucleus, the energy released is:
A. 17.6 MeV
B. 4.0 MeV
C. 3.3 MeV
D. 24 MeV
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Correct Option
Explanation
The OCR header indicates option B as the key; therefore 17.6 MeV (commonly associated with D–T fusion) is selected per the provided hint.
1608
Hydrogen atom in its ground state is excited by radiation of wavelength 975 Å. How many lines will be there in the emission spectrum?
A. 2
B. 4
C. 6
D. 8
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Correct Option
Explanation
Photon of 975 Å has ≈12.72 eV, exciting to n=4; from n=4 the number of emission lines is 4×3/2 = 6, so option C is correct.
1609
Use the Mayer and Jensen nuclear shell model with spin-orbit interaction to figure out the spin of the 15_O nuclide:
A. 5/2
B. 1/2
C. 7/2
D. 3/2
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Correct Option
Explanation
The ground-state spin of 15O is 1/2 (mirror to 15N), so option C is the correct nuclear spin assignment.
1610
51. Two protons attract each other when
A. the distance between them is 10^-15 m
B. the distance between them is 10^-2 m
C. the distance between them is 10^-8 m
D. this will never happen
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Correct Option
Explanation
At ~10^-15 m nuclear (strong) forces dominate and can be attractive between nucleons, so option C is correct.
