Question

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation energy of sodium atom? (c = 3 $\times$ 10${}^8$ ms${}^{-1}$, h = 6.626 $\times$ 10${}^{-34}$ J s)

• A. $5.6\times {10}^{-19}kJ$
• B. $6.9\times {10}^{-18}kJ$
• C. $8.2\times {10}^{-19}J$
• D. 495 kJ

Answer 1

The correct option is C $8.2\times {10}^{-19}J$

Given that,

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

Now,

E $=\frac{hc}{\lambda }=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{242\times {10}^{-9}}$

$=8.2\times {10}^{-19}J$