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1911
Hydrogen bomb is based on
A. controlled chain reaction
B. nuclear fission
C. nuclear fusion
D. uncontrolled chain reaction
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Correct Option
Explanation
The hydrogen bomb derives its huge energy from thermonuclear fusion, so option C is correct.
1912
68. γ rays are
A. high energy rays emitted by radioactive elements
B. uncharged high energy rays coming from the outer space
C. charged particles emitted by radioactive elements
D. charged particles coming from the outer space
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Correct Option
Explanation
Gamma rays are high-energy electromagnetic radiation emitted by radioactive elements, matching option C.
1913
By the use of radio-induced mutation, the plants:
A. Have shown more resistance to diseases
B. Give better yield and grain quality
C. Have shown more resistance to pest
D. All of these
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Correct Option
Explanation
Radio-induced mutations have produced traits including disease and pest resistance and improved yield/quality, so 'All of these' is correct.
1914
In the nuclear reaction between a deuteron and C-12, N-13 is produced. Which is the other particle liberated?
A. Proton
B. Neutron
C. Electron
D. Positron
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Correct Option
Explanation
12C + 2H → 13N + 1n conserves mass and charge (initial Z=7, final 13N has Z=7 and the extra nucleon is a neutron), so the liberated particle is a neutron.
1915
The majority of cosmic-ray particles at sea level are:
A. μ mesons
B. T-mesons
C. Tto mesons
D. None of these
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Correct Option
Explanation
At sea level the dominant secondary charged particles from cosmic rays are muons (μ mesons).
1916
The most familiar example of radioactive dating is
A. carbon dating
B. nitrogen dating
C. helium dating
D. hydrogen dating
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Correct Option
Explanation
Carbon dating (radiocarbon dating) is the most familiar example of radioactive dating.
1917
A gamma ray photon generates a collision with an electron at rest. During the process the change in the photon will be a decrease in ____.
A. Momentum and potential energy
B. Momentum and kinetic energy
C. Force and kinetic energy
D. None of these
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Correct Option
Explanation
In Compton scattering the photon transfers energy and momentum to the electron, so the photon's energy (and hence kinetic-equivalent) and momentum decrease.
1918
The first successful quantitative theory of atomic structure was formulated by
A. David Bohm
B. Neil Bohr
C. Stefan Boltzmann
D. Louis de-Broglie
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Correct Option
Explanation
Niels (Neil) Bohr formulated the first successful quantitative atomic model (Bohr model), so option C is correct.
1919
A photon of energy 4 eV is incident on a metal surface whose work function is 2 eV. The minimum reverse potential to be applied for stopping the emission of electrons is
A. 4 V
B. 2 V
C. 6 V
D. 8 V
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Correct Option
Explanation
Maximum kinetic energy = 4 eV − 2 eV = 2 eV, so the stopping potential equals 2 V.
1920
The total energy of the hydrogen atom is
A. positive
B. infinite
C. zero
D. negative
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Correct Option
Explanation
Bound states of the hydrogen atom have negative total energy (energy is less than that of a free electron at rest).
