Question

The frequency of a wave is $6 \times 10^{15} s ^{-1}$ Its wave number would be

• A. $10^{5} cm ^{-1}$
• B. $2 \times 10^{7} m ^{-1}$
• C. $2 \times 10^{7} cm ^{-1}$
• D. $2 \times 10^{5} cm ^{-1}$

Answer 1

Answer: (B)

Wave number $(\bar{v})=\frac{1}{\text { Wavelength }(\lambda)}=\frac{\text { Velocity (c)}}{\text {Frequency}(v)}$
$c= v \lambda$
$v=\frac{c}{\lambda}$
$v=c \times \bar{v}$
$\overline{ v }=\frac{ v }{ c }$
$\therefore \bar{v}=\frac{6 \times 10^{15} s ^{-1}}{3.0 \times 10^{8} m / s }$
$=2 \times 10^{7 m ^{-1}}$