Grade 10 Physical Sciences · Waves, Sound and Light

Calculate photon energy

Calculate the energy of one photon of light using E = hf or E = hc/λ.

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Question WE3 · Siyavula Grade 10 Physical Sciences, 11.5 Particle-like nature of EM radiation, Worked example 3 · 3 marks

WE3 Calculate the energy of a photon with a frequency of

3 \times 1 0^{18}

Hz.(3)

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More past paper questions: calculate photon energy

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3. Question 10.1.2 · November 2023 · Paper 1 · National (DBE) · 4 marks
10.1 Two small spheres, $A$ and $B$ , made of pure zinc are at rest $0, 1$ m apart on a wooden table. Sphere $A$ is negatively charged and is free to move on the table, while sphere $B$ is uncharged and fixed to the table, as shown in the diagram below.

High-intensity ultraviolet light of frequency $2, 8 \times 1 0^{16}$ Hz is now shone continuously onto sphere $B$ .

The work function of zinc is $6, 63 \times 1 0^{- 19}$ J.

Answer the questions that follow.
10.1.2 Explain, using a suitable calculation, why the ultraviolet light shone on sphere $B$ will eject electrons from its surface.(4)
Show the memo (4 ticks)Memo
1. ✓
  Formula $E = h f$
  1 mark · Calculate photon energy
2. ✓
  Substitution $E = (6, 63 \times 1 0^{- 34}) (2, 8 \times 1 0^{16})$
  1 mark · Calculate photon energy
3. ✓
  Answer $E = 1, 86 \times 1 0^{- 17}$ (J)
  1 mark · Calculate photon energy
4. ✓
  ComparisonSince $E > W_{0}$ (or $E - W_{0} > 0$ ), electrons will be ejected.
  1 mark · Explain the photoelectric effect
4. Question 10.1.2 · May/June 2022 · Paper 1 · National (DBE) · 4 marks
10.1 The apparatus illustrated in the simplified diagram below is used to demonstrate the photoelectric effect.
Incident light of frequency $1, 2 \times 1 0^{15}$ Hz is shone onto the metal plate and electrons are emitted.

Calculate the:
10.1.2 Number of photoelectrons emitted in one second if the total energy transferred by the light to the metal plate per second is $1, 75 \times 1 0^{- 9}$ J(4)
Show the memo (4 ticks)Memo
1. ✓
  FormulaFor one photon:
  $E = h f$
  1 mark · Calculate photon energy
2. ✓
  Substitution $E = (6, 63 \times 1 0^{- 34}) (1, 2 \times 1 0^{15}) = 7, 96 \times 1 0^{- 19}$ J
  1 mark · Calculate photon energy
3. ✓
  Number of photonsNo of $e^{-}$ = No of photons $= \frac{Total energy of photons}{Energy of one photon} = \frac{1 , 75 \times 1 0 ^{- 9}}{7 , 96 \times 1 0 ^{- 19}}$
  1 mark · Explain the photoelectric effect
4. ✓
  Answer $= 2, 2 \times 1 0^{9}$ ( $2, 198 \times 1 0^{9}$ )
  1 mark · Explain the photoelectric effect
5. Question 3.3.2 · November 2023 · Paper 1 · Provincial · 3 marks
The diagram below shows the wavelengths of frequencies of different types of electromagnetic radiation. Consider the diagram and answer the questions that follow.
3.3 A photon has a wavelength of $700$ nm.

Calculate the:
3.3.2 Frequency of the photon.(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $E = h f$
  1 mark · Calculate photon energy
2. ✓
  Substitution $2, 84 \times 1 0^{- 19} = 6, 63 \times 1 0^{- 34} f$
  1 mark · Calculate photon energy
3. ✓
  Answer with unit $f = 4, 29 \times 1 0^{14}$ Hz
  1 mark · Calculate photon energy

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