Question

What is the stopping potential, when a metal surface with work function \(1.2\,\text{eV}\) is illuminated with light of energy \(3\,\text{eV}\)?

• A. \(2.0\,\text{V}\)
• B. \(1.2\,\text{V}\)
• C. \(1.4\,\text{V}\)
• D. \(1.8\,\text{V}\)

Hint:

Stopping potential equals maximum kinetic energy of photoelectrons (in eV).

Answer 1

The Correct Option is D

Step 1: Use Einstein’s photoelectric equation.
\[ E = \phi + K_{\max} \]
Step 2: Substitute given values.
\[ K_{\max} = 3 - 1.2 = 1.8\,\text{eV} \]
Step 3: Relation with stopping potential.
\[ K_{\max} = eV_s \Rightarrow V_s = 1.8\,\text{V} \]
Step 4: Conclusion.
The stopping potential is \(1.8\,\text{V}\).