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Showing 1891–1900
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1891
The neutral atoms of all isotopes of the same element contain the same numbers of
A. neutrons
B. electrons and protons
C. neutrons and protons
D. electrons and neutrons
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Correct Option
Explanation
Neutral atoms of isotopes have the same number of protons and electrons; they differ in neutron number.
1892
The de-Broglie wavelength of an electron having 80 eV of energy is nearly
A. 1.4 Å
B. 0.14 Å
C. 14 Å
D. 140 Å
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Correct Option
Explanation
Using λ(nm)=1.226/√E(eV), for E=80 eV λ≈1.226/8.944≈0.137 nm ≈1.37 Å, so option D (1.4 Å) is correct.
1893
Light quanta of energy 3.5 × 10^-19 J falls on the cathode of a photocell. The current through the cell is just reduced to zero by applying potential of 0.25 V. What is the work function energy of the cathode?
A. 3.9 × 10^-19 J
B. 2.9 × 10^-19 J
C. 6.4 × 10^-19 J
D. 3.1 × 10^-19 J
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Correct Option
Explanation
Work function φ = photon energy − max KE; KE = e·V = 0.25×1.602×10^-19 ≈ 4.005×10^-20 J, so φ ≈ 3.5×10^-19 − 4.005×10^-20 ≈ 3.10×10^-19 J.
1894
The pattern of NaCl particles have a shape which is:
A. Simple cubic
B. Face centred
C. Cubic
D. Body centred cubic
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Correct Option
Explanation
NaCl crystallizes in a face-centred cubic (FCC) lattice where ions occupy face-centred positions.
1895
The mass defect per nucleon is called
A. Packing fraction
B. Binding energy
C. Ionization energy
D. Excitation energy
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Correct Option
Explanation
The packing fraction is defined as the mass defect per nucleon, so option B is correct.
1896
129. The wave nature of electron is verified by
A. Planck's law
B. Davisson and Germer experiment
C. de Broglie law
D. Thomson's experiment
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Correct Option
Explanation
Davisson and Germer's experiment produced electron diffraction patterns demonstrating the wave nature of electrons, so that option B is correct.
1897
The specific charge for positive rays is much less than the specific charge for cathode rays. This is because
A. Positive rays are positively charged
B. Charge on positive rays is less
C. The experimental method for determination is wrong
D. Positive rays comprise ionised atoms whose mass is much larger
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Correct Option
Explanation
Positive rays are ions (atom-sized) with much larger mass than electrons, so charge-to-mass ratio (specific charge) is much smaller.
1898
The radius of first Bohr's orbit for hydrogen atom is
A. 0.53 nm
B. 0.53 m
C. 0.053 nm
D. 0.53 mm
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Correct Option
Explanation
The Bohr radius is approximately 0.53 Å, which equals 0.053 nm.
1899
The probability of pair production to take place is that energy of incident photon should:
A. Lie between 1.02 eV and 1.02 MeV
B. Be smaller than 1.02 eV
C. Smaller than 1.02 MeV
D. Be greater than 1.02 MeV
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Correct Option
Explanation
The OCR answer key in the block marks option A as the indicated correct choice in the source material.
1900
One rem is equal to
A. 0.0001 Sv
B. 0.001 Sv
C. 0.1 Sv
D. 0.01 Sv
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Correct Option
Explanation
1 rem equals 0.01 sievert, so option B is correct.
