The rope shown at an instant is carrying a wave travelling towards right, created by a source vibrating at a frequency n . Consider the following statements

I. The speed of the wave is `4n xx ab`
II. The medium at a will be in the same phase as d after `(4)/(3n)s`
III. The phase difference between b and e is `(3pi)/(2)`
Which of these statements are correct

Options

A. I, II and III
B. II only
C. I and III
D. III only

Answer

C

Explanation

Speed `(v)=nlambda`
Here `lambda=ab+bc+cd+de`
`implies lambda=4ab` `[ab = lambda//4]`
Here, speed = `4n ab`
Path difference between b and e = `(3lambda)/(4)`
Phase difference `(Deltaphi)=(2pi)/(lambda)xx` Path difference
`=(2pi)/(lambda)xx(3lambda)/(4)=(3pi)/(2)`.