Question

The maximum kinetic energy $\left(E_{max}\right)$ of photoelectrons emitted in a photoelectric cell varies with frequency ($v$) as shown in the graph. The slope of the graph is equal to

• A. Charge of the electron
• B. $\frac{e}{m}$ of the electron
• C. Work function of the emitter
• D. Plank's constant

Answer 1

The correct option is D Plank's constant

Given energy of incident radiation $=h\nu$
Work function of the surface of the metal $=\varphi$
The excess energy from the radiation goes into increasing the kinetic energy of ejected photoelectron.
Hence
$E_k=h\nu -\varphi$ would give us the maximum kinetic energy of the ejected photoelectrons.
As we can see, if we compare this with the equation of a straight line (y = mx + c)
with frequency $\nu$ on the x axis and $E_k$ on the y axis. We get a straight line with slope of 'h' (Plank's constant).