When a metal surface is illuminated by light of wavelength λ$\lambda$, the stopping potential is 8 V$8\mathrm{\ V}$. When the same surface is illuminated by light of wavelength 3λ$3\lambda$, stopping potential is 2 V$2\mathrm{\ V}$. The threshold wavelength for this surface is:

Related Formula

Core Logic

Using Einstein's Photoelectric equation for the two cases:

Case 1 (Wavelength λ$\lambda$, Stopping Potential 8 V$8\mathrm{\,V}$):

Case 2 (Wavelength 3λ$3\lambda$, Stopping Potential 2 V$2\mathrm{\,V}$):

Step 2: Solving the Equations

Multiply equation (ii) by 4 to eliminate e$e$:

Equating this to equation (i):

Divide entirely by hc$hc$:

Chapter Mix

Class 12 Physics: Dual Nature Of Radiation And Matter