Question

A photoelectric-effect experiment finds a stopping potential of $1.56\mathrm{V}$when light of $200\mathrm{nm}$is used to illuminate the cathode.

a. From what metal is the cathode made?

b. What is the stopping potential if the intensity of the light is doubled?

Short answer

a. the metal is copper.

b. Stopping potential remains the same.

Step-by-step solution

Part (a) Step 1: Given information

We have given,

stopping potential =$1.56\mathrm{V}$

wavelength =$200\mathrm{nm}$

We have to find the metal from which it is made.

Simplify 

We can find the metal using the work function of the metal that is found out as,

$$\begin{gathered} \mathrm{W}=\mathrm{E}-{\mathrm{eV}}_0 \\ \mathrm{W}=\frac{1240\mathrm{eV}.\mathrm{nm}}{200\mathrm{nm}}-1.56\mathrm{eV} \\ \mathrm{W}=4.64\mathrm{eV} \end{gathered}$$

Then metal is copper.

Part (b) Step 1: Given information

We have given, the intensity of the light is doubled.

We have to find the stopping potential.

Simplify  

Since we already know that the stopping potential doesn't depends on the intensity of light. so if we changing the intensity then it doesn't effect the stopping potential.