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Light of energy 1.12 x 10\(^{-18}\) J is incident on a metal of ejected electrons with...

Physics
WAEC 2024

Light of energy 1.12 x 10\(^{-18}\) J is incident on a metal of ejected electrons with maximum energy of 8.0 x 10\(^{-19}\)J. Calculate the threshold frequency of the metal. [h = 6.626 x 10\(^{-34}\)Js] 

  • A. 4.8 x 10\(^{14}\)Hz
  • B. 1.2 x 10\(^{15}\)Hz
  • C. 1.7 x 10\(^{15}\)Hz
  • D. 2.8 x 10\(^{15}\)Hz
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Correct Answer: Option A
Explanation

E = hf + W\(_o\)

E = 1.12 x 10\(^{-18}\)J

Max. Energy = 8.0 x 10\(^{-19}\)J.

W\(_o\) = E - Max. Energy  = 1.12 x 10\(^{-18}\)J - 8.0 x 10\(^{-19}\)J. = 3.2 x 10\(^{-19}\)J.

But W\(_o\) = hf\(_o\)

f\(_o\) = \(\frac{W_o}{h}\) = \(\frac{3.2 \times 10^{-19}}{6.626 \times 10^{-34}}\) = 4.83 x 10\(^{14}\)Hz


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WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076
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