Question

The frequency of electromagnetic wave having wavelength $25mm$ is ____________ Hz

• A. $1·2\times {10}^{10}$
• B. $7·5\times {10}^5$
• C. $1·2\times {10}^8$
• D. $7·5\times {10}^6$

Answer 1

The correct option is A

$1·2\times {10}^{10}$

Step 1: Given data

The wavelength of electromagnetic wave

$$\begin{gathered} \left(\lambda \right)=25mm \\ \left(\lambda \right)=\frac{25}{1000} \\ \left(\lambda \right)=25\times {10}^{-3}m \end{gathered}$$

Step 2: Formula used

The frequency can be computed using the following formula:

$f=\frac{c}{\lambda },$ where $f=$frequency, $\lambda =$wavelength, and $c=3\times {10}^8$ speed of light.

Step 3: Compute the frequency

Substitute the known values in the formula $f=\frac{c}{\lambda }$,

$$\begin{gathered} f=\frac{3·0\times {10}^8}{25\times {10}^{-3}} \\ f=1·2\times {10}^{10}Hz \end{gathered}$$

So, the frequency of electromagnetic waves will be$1·2\times {10}^{10}Hz$.

Hence, option A is the correct answer.