Light of wavelength falls normally on a metallic surface in an evacuated…

PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation

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) (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