QCE Vault / Physics Physics — Question 20 QCAA 2020, Paper 1 · 1 mark
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QUESTION 20 Calculate the frequency of light that would be required to eject a photoelectron at a velocity of 1.90 × 10 6 m s − 1 1.90 \times 10^{6}\,\mathrm{m\,s^{-1}} 1.90 × 1 0 6 m s − 1 from a metal plate with a work function of 4.73 eV. (A) 1.14 × 10 15 H z 1.14 \times 10^{15}\,\mathrm{Hz} 1.14 × 1 0 15 Hz (B) 1.34 × 10 15 H z 1.34 \times 10^{15}\,\mathrm{Hz} 1.34 × 1 0 15 Hz (C) 2.48 × 10 15 H z 2.48 \times 10^{15}\,\mathrm{Hz} 2.48 × 1 0 15 Hz (D) 3.62 × 10 15 H z 3.62 \times 10^{15}\,\mathrm{Hz} 3.62 × 1 0 15 Hz WORKED SOLUTION
Answer D 1 mark Worked solution
Use h f = ϕ + 1 2 m e v 2 hf=\phi+\frac12m_ev^2 h f = ϕ + 2 1 m e v 2 . Substituting ϕ = 4.73 \phi=4.73 ϕ = 4.73 eV and v = 1.90 × 10 6 m s − 1 v=1.90\times10^6\,\mathrm{m\,s^{-1}} v = 1.90 × 1 0 6 m s − 1 gives f ≈ 3.62 × 10 15 f\approx3.62\times10^{15} f ≈ 3.62 × 1 0 15 Hz. Option D. Worked explanation by QCE Vault; correct option verified against the QCAA answer key.