The work function for metals A, Band C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einstein's equation the metals which will emit photo, electrons for a radiation of wavelength 4100 A^o is/are

none

A only

A and B only

All the three metals

Solution

A and B only

Work function for wavelength of 4100 A^o is

W = $\frac{h c}{λ}$

W = $\frac{6.63 \times 10^{- 34} \times 3 \times 10^{8}}{4100 \times 10^{- 10}}$

W = 4.8 × 10^-19J

W = $\frac{4.8 \times 10^{- 19}}{1.6 \times 10^{- 19}}$ eV

W = 3 eV

Now we have,

W_A = 1.22 eV

W_B = 2.0 eV

W_C = 5 eV

Since W_A < W and W_B < W hence A and B will emit photoelectrons.

So only metals having a work function less than 3 eV can emit photoelectrons for the incident of wavelength 4100 A^o.

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