Question

If the wavelength of the electromagnetic radiation is increased to thrice the digital value, then what will be the percent change in the value of frequency of the electromagnetic radiation.

• A. Increases by $33 \%$
• B. Decreases by $33 \%$
• C. Increases by $66 \%$
• D. Decreases by $66 \%$

Answer 1

Answer: (D)

$ v_1=\frac{c}{\lambda_1} $
$v_2=\frac{c}{\lambda_2}=\frac{c}{3 \lambda_1}$
$\%$ change in frequency $=\frac{v_2-v_1}{v_1} \times 100$
$=\frac{\frac{c}{3 \lambda_1}-\frac{c}{\lambda_1}}{\frac{c}{\lambda_1}} \times 100=\frac{-\frac{2 c}{3 \lambda_1} \times 100}{\frac{c}{\lambda_1}}=-66 \%$