Question

The work functions for metals A, B and C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einstein's equation the metals which will emit photoelectrons for a radiation of wavelength 4100 $\mathring{A}$ is/are

• A. A only
• B. A and B only
• C. all the three metals
• D. none

Answer 1

Answer: (B)

A and B only

Answer 2

\begin{array} \ A \\\ 1.92eV\\\ \end {array} \begin {array} \ \ \ \ B \\\ \ \ 2.0eV \\\ \end {array}\begin {array}\ \ \ \ \ \ \ \ C \\\ \ \ \ \ \ 5.0eV\\\ \end {array} $E= \frac {hc}{\lambda}= \frac {6.63 \times 10^{-34}\times 3 \times 10^8}{41 \times 10^{-8}}$ $=\frac {19.89 \times 10^{-18}}{41 \times 1.6 \times 10^{-19}}eV$ $E= \frac {19.89 \times 10}{41 \times 1.6}=\frac {198.9}{65.6}eV$ As energy of incident radiation is nearly equal to 3.0 eV, thus it only able to emit photoelectron from A and B which having work functions 1.92 eV and 2.0 eV respectively.