Exams › JEE Advanced › Physics
The kinetic energy (KE) of a photoelectron emitted when light of frequency v strikes a metal surface obeys KE = hv - phi, where phi is the work function. Which of the following correctly describe(s) the graph of KE versus incident frequency?
- A straight line whose slope equals Planck's constant h
- A straight line whose x-intercept equals the product of the threshold frequency and Planck's constant
- A straight line whose extrapolated y-intercept equals the negative of the threshold energy (work function)
- A straight line whose x-intercept equals the threshold frequency
Correct answer: A straight line whose slope equals Planck's constant h
Solution
The equation KE = hv - phi is linear in v. The slope is h (Planck's constant), the x-intercept occurs at the threshold frequency v₀ = phi/h (not h*v₀), and the extrapolated y-intercept is -phi (negative of threshold energy, not equal to it). Option A and D are correct; option B is incorrect (x-intercept = v₀, not h*v₀); option C states intercept equals threshold energy but it is actually -phi (negative).
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