Question

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. What is the ionisation energy of sodium per atom?

• A. $494.5\times {10}^{-6}J/atom$
• B. $8169.5\times {10}^{-10}J/atom$
• C. $5.85\times {10}^{-15}J/atom$
• D. $8.214\times {10}^{-19}J/atom$

Answer 1

The correct option is D $8.214\times {10}^{-19}J/atom$

Ionizationn energy=Energy of photon, $E=hc/\lambda$

where, $h=6.626\times {10}^{-34}Js,c=3\times {10}^{8}m{s}^{-1}$

Given $\lambda =242nm=242\times {10}^{-9}m$

$E=6.626\times {10}^{-34}\times 3\times {10}^8/(242\times {10}^{-9})$

$E=0.0821\times {10}^{-17}=8.21\times {10}^{-19}J$ for each sodium atom

option D