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WAEC Physics 2024 Paper

Question : 25

Total: 50

^{-18}

^{-19}

^{-34}

Js]

Solution:

Concept:

The photoelectric equation is

E = W_o + KE_{\text{max}}

, where the work function

W_o

gives the threshold frequency.

Explanation:

The energy of the incident photon is

E = 1.12 \times 10^{-18}\ \text{J}

The maximum kinetic energy of the ejected electron is

KE_{\text{max}} = 8.0 \times 10^{-19}\ \text{J}

Calculate the work function of the metal:

W_o = E - KE_{\text{max}}

W_o = 1.12 \times 10^{-18} - 8.0 \times 10^{-19} = 3.2 \times 10^{-19}\ \text{J}

The work function is related to threshold frequency by

W_o = h f_o

Solve for threshold frequency:

f_o = \dfrac{W_o}{h} = \dfrac{3.2 \times 10^{-19}}{6.626 \times 10^{-34}}

f_o = 4.83 \times 10^{14}\ \text{Hz} \approx 4.8 \times 10^{14}\ \text{Hz}

Answer:

Option A:

4.8 \times 10^{14}\ \text{Hz}

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