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.

Solution :
$$\eqalign{ & {\nu _1} = \frac{c}{{{\lambda _1}}} \cr & {\nu _2} = \frac{c}{{{\lambda _2}}} = \frac{c}{{3{\lambda _1}}} \cr & \% \,{\text{change in frequency}} \cr & = \frac{{{\nu _2} - {\nu _1}}}{{{\nu _1}}} \times 100 \cr & = \frac{{\frac{c}{{3{\lambda _1}}} - \frac{c}{{{\lambda _1}}}}}{{\frac{c}{{{\lambda _1}}}}} \times 100 \cr & = \frac{{ - \frac{{2c}}{{3{\lambda _1}}} \times 100}}{{\frac{c}{{{\lambda _1}}}}} \cr & = - 66\% \cr} $$