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Atomic and nuclear physics
5 NET Physics questions with answers and explanations.
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What is the energy of the electron in the ground state of the hydrogen atom?
- 1 -13.6 eV
- 2 -3.4 eV
- 3 +13.6 eV
- 4 0 eV
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Correct answer: -13.6 eV
In the Bohr model the ground state energy of hydrogen is -13.6 eV.
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The transition of an electron in hydrogen from n = 3 to n = 2 belongs to which series?
- 1 Lyman
- 2 Balmer
- 3 Paschen
- 4 Brackett
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Correct answer: Balmer
Transitions ending at n = 2 form the Balmer series, which lies partly in the visible region.
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A radioactive sample has a half-life of 10 days. What fraction is left after 30 days?
- 1 1/3
- 2 1/6
- 3 1/8
- 4 1/9
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Correct answer: 1/8
30 days is three half-lives, so the fraction left is (1/2)^3 = 1/8.
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Which particle is neutral and has a mass close to that of a proton?
- 1 Electron
- 2 Neutron
- 3 Positron
- 4 Neutrino
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Correct answer: Neutron
The neutron carries no charge and has almost the same mass as the proton.
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How many neutrons are in a nucleus of uranium-235? (Atomic number 92)
- 1 92
- 2 235
- 3 143
- 4 327
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Correct answer: 143
Neutrons = mass number - atomic number = 235 - 92 = 143.