Chapter 7 - Atomic Structure and Periodicity - Exercises - Page 342: 43

$9.38\times 10^{14}Hz$ to $1.07\times 10^{15}Hz$

We know that $v=\frac{c}{\lambda}$ $\implies v=\frac{3\times 10^8\frac{m}{s}}{\lambda}\times \frac{10^9nm}{1m}$.......eq(1) If $\lambda=280nm$ then substituting values in equation(1),we obtain $v=1.07\times 10^{15}Hz$ and if $\lambda=320nm$ then equation gives us $v=9.38\times 10^{14}Hz$