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Nuclear physics and semiconductors
5 ECAT Physics questions with answers and explanations.
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The binding energy per nucleon is greatest for nuclei with mass number around:
- 1 4
- 2 56
- 3 120
- 4 238
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Correct answer: 56
Iron-56 and nearby nuclei are the most tightly bound, so fission of heavy nuclei and fusion of light ones release energy.
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In an n-type semiconductor, the majority charge carriers are:
- 1 Holes
- 2 Electrons
- 3 Protons
- 4 Positrons
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Correct answer: Electrons
Doping with a donor such as phosphorus adds free electrons, which become the majority carriers.
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When a p-n junction diode is forward biased, the depletion region:
- 1 Widens
- 2 Narrows
- 3 Disappears for good
- 4 Stays unchanged
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Correct answer: Narrows
Forward bias pushes carriers toward the junction, so the depletion region becomes narrow and current flows.
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An alpha particle consists of:
- 1 Two protons and two neutrons
- 2 One proton and one neutron
- 3 Two electrons
- 4 A single neutron
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Correct answer: Two protons and two neutrons
An alpha particle is the nucleus of a helium-4 atom: two protons and two neutrons.
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Nuclear fission is the process in which:
- 1 Two light nuclei join to form a heavier nucleus
- 2 A heavy nucleus splits into two lighter nuclei, releasing energy
- 3 An electron leaves the atom
- 4 A nucleus absorbs a photon only
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Correct answer: A heavy nucleus splits into two lighter nuclei, releasing energy
In fission, a heavy nucleus such as uranium-235 splits after absorbing a neutron and releases a large amount of energy.