DSE Physics: Atomic World (Elective) — Practice Questions & Answers

In the Bohr model the energy of the hydrogen atom is E_n = -13.6/n² eV. The negative sign indicates that the electron is

• bound to the nucleus
• moving away from the nucleus
• positively charged
• at rest

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In the Bohr model the orbital radius is proportional to n². The ratio of the radius in the first excited state (n = 2) to that in the second excited state (n = 3) is

• 4 : 9
• 2 : 3
• 1 : 2
• 9 : 4

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The energy needed to remove the electron from a ground-state (n = 1) hydrogen atom is

• 13.6 eV
• 3.4 eV
• 1.5 eV
• 27.2 eV

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In E_n = -13.6/n² eV, the sign shows the electron is bound and energy is needed to free it.

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Answer: negative / minus

In the Bohr model the radius of an allowed orbit is proportional to n to the power (a power of the quantum number).

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Answer: 2 / two / squared

The minimum energy needed to ionise a hydrogen atom in its ground state is eV.

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Answer: 13.6 / 13.6 eV

Photons of energy 7 eV strike a metal and eject electrons with a maximum kinetic energy of 4 eV. The work function of the metal is

• 3 eV
• 11 eV
• 4 eV
• 1.75 eV

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For the metal above (work function 3 eV), photons of energy 4 eV are used. The stopping potential is

• 1 V
• 0 V
• 3 V
• 4 V

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In the photoelectric effect, increasing the intensity of light (at the same frequency) increases the

• number of photoelectrons emitted per second
• maximum kinetic energy of each electron
• work function of the metal
• threshold frequency

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The minimum energy needed to release an electron from a metal surface is called the function.

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Answer: work