If the frequency of a wave is increased by `25%`, then the change in its wavelength will be: (medium not changed)

Options

A. `20%` increase
B. `20%` decrease
C. `25%` increase
D. `25%` decrease

Answer

B

Explanation

Since, the medium has not changed, speed of wave remains same.
`impliesv=flamda=`constant
`f_1lamda_1=f_2lamda_2`
`impliesf_1lamda_1=(1.25f_1)lamda_2` (`:.` frequency increased by `25%`)
`lamda_2=(lamda_1)/(1.25)implies_2` decreases.
`%` change in wavelength `=(lamda_1-lamda_2)/(lamda_1)xx100`
`(lamda_1-(lamda_1)/(1.25))/(lamda_1)xx100=(0.25)/(1.25)xx100=(100)/(5)=20%`