The stopping potential for electrons from a photosensitive surface illuminated by light of wavelength 491 nm is 0.710V. When the incident wavelength is changed to a new value, the stopping potential is 1.43V. The new wavelength is:
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a
309 nm
b
329 nm
c
382 nm
d
400 nm
answer is C.
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Detailed Solution
Energy of photon, E=1240λ(nm)eV⇒E=1240491eV⇒E=2.53eV Work function =ϕ0=E−V0e=2.53−0.710=1.82eVFor case 2 , work function wil remain same⇒E=hcλ-ϕo⇒Voe=E-ϕo⇒1.43+ϕo=E⇒1.43+1.82=E⇒E=3.25eVSo, λ=12403.25nm=382nm