Physics

Problem

Light of wavelength

450\,\text{nm}

falls normally on a metallic surface in an evacuated photoelectric cell. The saturation photocurrent reaches

12\,\mu\text{A}

at a collector potential of

+3.0\,\text{V}

, and the photocurrent drops to zero at a retarding potential of

1.8\,\text{V}

. (a) Draw a neat, qualitative

I

–

V

curve for the given conditions, marking the saturation region, knee of the curve, and stopping potential. (b) Calculate: (i) the maximum kinetic energy

K_{\text{max}}

of the emitted electrons in electron-volt, (ii) the work function

\phi

of the metal in electron-volt. (c) If the wavelength of the incident light is changed to

400\,\text{nm}

while keeping the intensity the same, how will the

I

–

V

curve be modified? Sketch the new curve on the same axes and justify your answer. a. (a) Sketch the

I

–

V

curve for

\lambda = 450\,\text{nm}

, indicating

I_{\text{sat}}

, the knee, and

V_0 = 1.8\,\text{V}

. b. (b)(i) Determine

K_{\text{max}}

in eV from the given stopping potential. c. (b)(ii) Compute the work function

\phi

of the metal in eV. d. (c) Draw and label the modified curve for

\lambda = 400\,\text{nm}

on the same axes, and explain the changes in

I_{\text{sat}}

and

V_0

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