Syllabus Edition

First teaching 2023

First exams 2025

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Energy Levels in Atoms & Line Spectra (CIE A Level Physics)

Exam Questions

1 hour8 questions
1a
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2 marks

Fig 1.1 shows some of the energy levels of the hydrogen atom.

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Calculate the energy of radiation emitted when an electron falls from level n = 3 to the ground state in the hydrogen atom.

1b
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3 marks

When electrons in a sample of hydrogen atoms relax from n  = 3, multiple frequencies of photons are emitted.

Sketch arrows on Fig 1.1 to show the transitions responsible for these photons.

1c
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4 marks

Calculate the wavelength of the photon with the smallest energy. Give your answer to an appropriate number of significant figures.

1d
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2 marks

One way to excite a hydrogen atom is by the absorption of a photon. 

Explain why, for a particular transition, the photon must have an exact amount of energy.

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2a
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2 marks

The lowest energy levels of a hydrogen atom are represented in Fig 1.1. The diagram is not to scale.

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Fig 1.1

Use Fig 1.1 to identify the transition which produces a photon with frequency of 2.93 × 1015 Hz.

2b
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3 marks

An excited hydrogen atom can emit photons of certain discrete frequencies in various regions of the electromagnetic spectrum. Three possible transitions are shown in Fig 1.2.

2-5-s-q--q2b-medium-aqa-a-level-physics

Fig 1.2

Identify the transitions in Fig 1.2 which produce a photon in the following region of the electromagnetic spectrum: 

  • Visible
  • Ultraviolet
  • Infrared
2c
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1 mark

State the meaning of the term 'ionisation'.

2d
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1 mark

State the minimum amount of energy required to ionise an electron from the ground level of hydrogen.

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3a
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2 marks

A continuous spectrum contains all wavelengths of light in a range.

Each element has a characteristic emission spectrum. Explain why this emission spectrum is not continuous.

3b
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1 mark

White light is passed through a low density sample of unknown gas.

State the type of spectrum formed.

3c
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2 marks

Explain why the spectrum from part (b) is not continuous.

3d
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2 marks

The spectrum obtained in part (b) can be used to identify the unknown gas. 

Explain how.

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1a
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4 marks

The energy levels of a hydrogen atom are shown in Fig. 1.1.

                                                                                  

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Fig. 1.1 

Calculate the wavelength of radiation emitted when an electron falls from level n = 4 to the ground state in the hydrogen atom.

1b
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3 marks

When an electron of energy 1.84 × 10−17 J collides with a hydrogen atom, photons of six different energies are emitted.  

Sketch arrows on Fig. 1.1 to show the transitions responsible for these photons. 

1c
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3 marks

Calculate the wavelength of the photon with the smallest energy. Give your answer to an appropriate number of significant figures. 

1d
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2 marks

One way to excite a hydrogen atom is by the absorption of a photon. 

Explain why, for a particular transition, the photon must have an exact amount of energy. 

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2a
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2 marks

The lowest energy levels of a hydrogen atom are represented in Fig. 1.1. 

22-3-2a-m-energy-levels-j-sq-cie-a-level

Fig 1.1

 

Identify the transition that produces a photon with frequency of 3.3 × 1016 Hz.

2b
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3 marks

An excited hydrogen atom can emit photons of certain discrete frequencies in various regions of the electromagnetic spectrum. Three possible transitions are shown in Fig. 1.2.

 22-3-2b-m-energy-levels-j-with-transitions-sq-cie-a-level
Fig. 1.2
 

Identify the transitions in Fig. 1.2 which produce a photon in the following regions of the electromagnetic spectrum:

(i)
Ultraviolet
[1]
(ii)
Visible
[1]
(iii)
Infrared
[1]
2c
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3 marks

Explain why the emitted photons in part (b) have certain discrete frequencies.

2d
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3 marks

An electron in the hydrogen atom is ionised by a photon of light with frequency 5.2 × 1016 Hz. 

Calculate the kinetic energy of the ionised electron.

 

kinetic energy .................................... J 

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3a
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5 marks

Transitions between three energy levels in a particular atom give rise to three spectral lines.

In decreasing magnitudes, these are related to the wavelengths, λ1, λ2, and λ3,  

Use a diagram to show that the equation that relates λ1, λ2, and λ3 is:

 

1 over lambda subscript 1 space equals space 1 over lambda subscript 2 space plus space 1 over lambda subscript 3 

3b
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6 marks

An atom has a ground state energy of −8.80 eV. The complete line emission spectra for this atom is shown in Fig. 1.1.

 22-3-3b-m-emission-spectra
Fig. 1.1
 

Sketch a diagram of the possible energy levels for the atomic line spectra shown in Fig 1.1. Label each energy level with the value of its energy.

 

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1a
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3 marks

Unstable nuclei can decay in a variety of ways. 

Electron capture is one such process, during which the nucleus ‘captures’ an orbiting inner-shell electron. The resulting nucleus has one less proton and one more neutron. Sometimes this process is accompanied by the emission of a characteristic X-ray photon, as illustrated in Fig. 1.1.

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Fig. 1.1

Explain why an X-ray photon is produced in this process and suggest why it is called ‘characteristic’.

1b
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5 marks

The Auger Effect is a process that sometimes accompanies that illustrated in Fig. 1.1. This process involves the emission of an electron – called an Auger electron – from the atom when a core electron is removed, leaving a vacancy. This is illustrated in Fig. 1.2.

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Fig. 1.2

This emission occurs if sufficient X-ray energy is transferred to outer shell electrons during the process. 

Show that the speed of a typical Auger electron is around 22% of the speed of light, stating any assumptions you make in your calculation.

            (Typical X-ray wavelength is ~ 10–10 m).

1c
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3 marks

Auger electrons tend to have very high energies. At such high energies, their wave-like nature can be used to investigate the structure of crystalline solids. 

When a beam of high-energy electrons is sent through a regularly spaced array of crystal atoms, they form a diffraction pattern of concentric bright and dark rings on a fluorescent screen, as shown in Fig. 1.3.

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Fig. 1.3

It can be shown that the angle of electron-diffraction θ  is related to the diameter of an atomic nucleus d  by the equation 

sin θ  = 1.22lambda over d 

Suggest what the term λ in the equation represents and describe how the observed diffraction pattern will vary in response to it.

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2a
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5 marks

Transitions between three energy levels in a particular atom give rise to three spectral lines. In decreasing magnitudes, these are f subscript 1, f subscript 2 and f subscript 3.

Show that the equation which relates f subscript 1, f subscript 2 and f subscript 3 is: 

f subscript 1 equals f subscript 2 plus f subscript 3

Sketch a suitable diagram to illustrate your answer.

2b
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6 marks

Fig. 1.1 shows the complete line emission spectrum for another particular atom.

2-5-s-q--q2b-hard-aqa-a-level-physics

Fig. 1.1

This atom has a ground state energy of  –10.0 eV. 

Sketch a diagram of the possible energy levels for the atomic line spectrum shown in Fig. 1.1. 

Label each energy level with the value of its energy.

2c
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3 marks

Explain the significance of an electron at an energy level of 0 eV.

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