The work function of a metal is in the range of 2 eV to 5 eV. Find which of the following wavelength of light cannot be used for photoelectric effect. (Consider, Planck's constant `=4xx10^(-15)" eV - s, velocity of light "=3xx10^(8)ms^(-1))`

Options

A. 510 nm
B. 650 nm
C. 400 nm
D. 570 nm

Answer

B

Explanation

Range of work function of metals = (2 to 5)eV `hc = 4 xx 10^(-15) eVs xx 3 xx 10^(8) ns^(-1) = 1200` eV - nm
As, `lambda = (hc)/(E)`
`lambda_(min) = (1200 eV-nm)/(5 eV) = 240` nm
` lambda_(max) = (1200 eV-nm)/(2eV) = 600` nm
Hence light of wavelength , 650 nm cannot be used for photoelectric effect.