First slide

Photo Electric Effect

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 $\overset{o}{A}$ are

Easy

A

none
B

A only
C

A and B only
D

all the three medals

Solution

Work function for wavelength of 4100 $\overset{o}{A}$ is
$\begin{array}{l} W = \frac{hc}{λ} = \frac{6 .62 \times 10^{- 34} \times 3 \times 10^{8}}{4100 \times 10^{- 10}} = 4 .8 \times 10^{- 19} J \\ = \frac{4 .8 \times 10^{- 19}}{1 .6 \times 10^{- 19}} eV = 3 eV \\ Now, we have \\ W_{A} = 1 .92 eV, W_{B} = 2 .0 eV, W_{C} = 5 eV since W_{A} < W and W_{B} < W, \\ hence, A and B will emit photoelectrons . \end{array}$

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