Question

When a wave passes through a boundary and into a new medium, which of the following characteristic of this wave don't change? And which do? a) wavelength b) Frequency c) speed d) both a and b e) none

Answer 1

Let's consider a wave travelling from one medium to another medium.Let the first medium is rare medium(air) and the second medium is denser medium(water). since the 2nd medium is denser its refractive index is more as compared to medium-1. The velocity of the wave inside a medium can be written as

where v = velocity of the wave in medium

c = velocity of the wave in free space

n = refractive index.

since the 2nd medium has more refractive index(n) so velocity will be less in 2nd medium. So the velocity of the wave changes when trevelling from medium-1 to medium-2.

Now the frequency of the wave depends on the source from which the wave is generated. so it's independent of the medium. so the frequency will remain constant.

Now wavelength of the wave is given by

where v =velocity of the wave

f =frequency of the wave.

Now we know that v will decrease. so the keep frequency constant wavelength has to be decrease.

So wavelength and speed of the wave changes while frequency remains constant.