When ultraviolet light of wavelength 100 nm is incident upon silver plate, a potential of 7.7 V is required to stop the photoelectrons from reaching the collector plate. How much potential will be required to stop the photoelectrons when light of wavelength 200 nm is incident upon silver?

1.5 V

$λ_1=\frac{12375}{E_1(eV)}Å=1000Å$

$∴E_1=12.375eV$

Similarly, $\frac{12375}{λ_2(Å)}eV=\frac{12375}{2000}= 6.1875eV$

Now, $E_1-W_0=eV_s$

and $E_2-W_0=eV_s$

Hence, $12.375−W_0 = 7.7eV_s$

and $6.1875−W_0 = eV_s$

Solving, we get $V_s =1.5V$