A string of length `0.4 m` and mass `10^(-2) kg` is clamped at one end . The tension in the string is `1.6 N`. The identical wave pulses are generated at the free end after regular interval of time , `Delta t` . The minimum value of `Delta t` , so that a constructive interference takes place between successive pulses is

Options

A. `0.1 s`
B. `0.05 s`
C. `0.2 s`
D. constructive interference cannot take place

Answer

C

Explanation

Velocity of wave on string ` = sqrt(T//mu) = 8 m//s`.
The pulse gets inverted after reflection from the fixed end , so for constructive interference to take place between successive pulses , the first pulse has to undergo two reflections from the fixed end .
So , `Delta t = ( 2xx 0.4 + 2 xx 0.4)/(8) = 0.2 s`