MHTCET 2016 Physics Solved Paper

(d) According to Einstein's photoelectric equation

hc

λ

−ϕ=eV
For wavelength λ, stopping potential is V
Now, equation becomes

hc

λ

−ϕ=eV .......(i)
For wavelength 3λ , stopping potential is

V

6

Now equation becomes

hc

3λ

−ϕ=

eV

6

⇒

2hc

λ

−ϕ=eV .....(ii)
Subtracting (i) and (ii)

2hc

λ

=eV+6ϕ ⇒

hc

λ

=eV+ϕ

hc

λ

=5ϕ and ϕ=

hc

λ0

Thus, we get λ0 = 5λ