Question

The energy required to remove an electron from the surface of Sodium metal is $ \, 2.3 \, eV.$ What is the longest wavelength of radiation with which it can show photoelectric effect?

• A. $5.4\times 10^{- 17 \, }m$
• B. $5.4\times 10^{- 8 \, }m$
• C. $5.4\times 10^{- 7 \, }m$
• D. $5.4\times 10^{- 9 \, }m$

Answer 1

Answer: (C)

Energy required to show photo emission $=2.3 \, eV$
$=2.3 \, \times 1.6\times 10^{- 19 \, }J \, $
Thus $E \, = \, \frac{h c}{\lambda } \, \, or \, \, \lambda =\frac{h c}{E}=\frac{6.626 \times 10^{- 34} \times 3 \times 10^{8}}{2.3 \times 1.6 \times 10^{- 19}}$
$= \, 5.4 \, \times 10^{- 7 \, }m.$
Thus, longest wavelength to show photoelectric effect $=5.4 \, \times 10^{- 7 \, }m.$