Photoelectric Effect Experiment

00:00 13 marks

In a photoelectric effect experiment, light of frequency \(f\) is incident on a metal surface with work function \(\Phi\). The maximum kinetic energy of the emitted photoelectrons is \(E_{max}\).

Part a

4 minutes 4 marks

Question

Describe the photoelectric effect and explain why it provides evidence for the particle nature of light. [4]

Hint Hint

Hint

Focus on the threshold frequency, the dependence of kinetic energy on light frequency (not intensity), and the instantaneous emission of electrons.

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Complete Answer

The photoelectric effect is the emission of electrons from a metal when light of sufficient frequency strikes it. It demonstrates the particle nature of light because (1) there is a threshold frequency below which no electrons are emitted, (2) the kinetic energy of the electrons depends on the frequency of the light rather than its intensity, and (3) the emission is instantaneous.

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Part b

1 minutes 1 marks

Question

State the equation relating \(E_{max}\), \(f\), and \(\Phi\). [1]

Hint Hint

Hint

Recall Einstein’s photoelectric equation.

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Complete Answer

\(E_{max} = hf – \Phi\)

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Part c(i)

3 minutes 2 marks

Question

Calculate the energy of an incident photon in eV. [2]

Hint Hint

Hint

Use \(E = \frac{hc}{\lambda}\) and then convert the result from Joules to electronvolts.

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\(E_{photon} \approx 2.76\,eV\)

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Part c(ii)

1 minutes 1 marks

Question

Determine the maximum kinetic energy of the emitted photoelectrons in eV. [1]

Hint Hint

Hint

Subtract the work function (2.3 eV) from the photon energy calculated in part (c)(i).

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\(E_{max} = 2.76\,eV – 2.3\,eV \approx 0.46\,eV\)

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Part c(iii)

1 minutes 1 marks

Question

Calculate the stopping potential required to prevent any photoelectrons from reaching the collector plate. [1]

Hint Hint

Hint

Use the relation \(eV_s = E_{max}\), so \(V_s = \frac{E_{max}}{e}\).

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\(V_s \approx 0.46\,V\)

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Part d

4 minutes 4 marks

Question

State and explain the effect of increased light intensity on the maximum kinetic energy of the photoelectrons and the photoelectric current. [4]

Hint Hint

Hint

Remember that \(E_{max}\) depends only on the frequency of the light, while the current is proportional to the number of photons per unit time.

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Complete Answer

The maximum kinetic energy \(E_{max}\) remains unchanged since it depends solely on \(hf\) and \(\Phi\), but the photoelectric current increases because a higher intensity means more incident photons and therefore more emitted electrons.

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