Question

A string of length 0.4m and mass 10^(-2) kg is tightly clamped at its ends. The tension in the string is 1.6N. Identical wave pulses are produced at one end at equal intervals of time, ∆t. The minimum value of ∆t which allows constructive interference between successive pulses is?

(a) 0.05s

(b) 0.10s

(c) 0.20s

(d) 0.40s

This question was addressed to me during an online interview.

My query is from Transverse Waves in portion Waves of Engineering Physics I

Answer 1

The correct answer is (b) 0.10s

For explanation: Mass per unit length of the string,

m=10^-2/0.4=2.5×(10^-2)kg/m

Velocity of the wave in the string,

v=√(T/m)=√(1.6/(2.5×10))=8m/s

For constructive interference between successive pulses, the minimum time interval is

∆tmin=2L/v=(2×0.4)/8=0.10s.