Question

Calculate the frequency of a wave with wavelength $4\times {10}^7$ nm .

• A. $7.5\times {10}^9{\text{s}}^{-1}$
• B. $7.5\times {10}^6{\text{s}}^{-1}$
• C. $2.5\times {10}^9{\text{s}}^{-1}$
• D. $2.5\times {10}^6{\text{s}}^{-1}$

Answer 1

The correct option is A $7.5\times {10}^9{\text{s}}^{-1}$

Given,
Wavelength $\left(\lambda \right)=4\times {10}^7\text{nm}=4\times {10}^{-2}\text{m}$
Again we know,
$c=\lambda v$, where c is velocity of light.
Therefore,
frequency $\left(v\right)=\frac{c}{\lambda }=\frac{3\times {10}^8{\text{m s}}^{-1}}{4\times {10}^{-2}\text{m}}=7.5\times {10}^9{\text{s}}^{-1}$