Q.Sketch, in words, the graph of stopping potential $V_0$ versus frequency $\nu$ of the incident light for a given metal surface, and explain how both Planck's constant and the metal's work function can be obtained from this graph.

The graph. Plotting the measured stopping potential $V_0$ against the frequency $\nu$ of the incident light, for a single metal, gives a straight line of positive slope that does NOT pass through the origin -- it crosses the frequency axis at a positive value $\nu_0$ (Section 11.4, Figure 2).

Reading off $h$. Einstein's equation, rearranged as $V_0=\dfrac{h}{e}\nu-\dfrac{\phi_0}{e}$, shows this line's SLOPE is exactly $h/e$. Since the electronic charge $e$ is independently known, measuring the slope of this experimental line gives a direct, independent experimental determination of Planck's constant $h$ -- a value found (originally by Millikan) to agree closely with the value obtained from Planck's own black-body radiation work, strong independent confirmation of Einstein's equation. …

Write Einstein's equation in the $V_0=(h/e)\nu-\phi_0/e$ slope-intercept form, then read off what the slope and the …

• Reading the graph's VERTICAL-axis intercept as $\phi_0$ directly (in volts) -- it is $-\phi_0/e$, so $\phi_0$ must still be obtained by multiplying by $e$ (or, more simply, by reading the horizontal intercept $\nu_0$ and using $\phi_0=h\nu_0$). …