A metallic surface is irradiated with monochromatic light of variable wavelength. Above a wavelength of `5000 Å` no photoelectrons are emitted from the surface. With an unknown wavelength, stopping potential fo 3V is necessary ot eliminate the photo current. Find the unknown wavelength.

Options

A. 2262 nm
B. 2272 Å
C. 1240 Å
D. 4524 Å

Answer

B

Explanation

According to quesiton, `lambda=5000 Å` and `V=3V`. Using equation of photoelectric equation ,
`K_(max)=E- phi_0 " " (K_(max) = eV_s)`
`3 xx 1.6 xx 10^(-19) = hc (1/lambda - (1)/(5000 xx 10^(-10)))`
` 3 xx 1.6 xx 10^(-19) = 6.63 xx 10^(-34) xx 3 xx 10^(8) (1/lambda -2 xx 10^(6))`
`1/lambda = 4.4 xx 10^(6) rArr lambda =2272 ` Å