Question

A string of length $0.4m$ and mass ${10}^{-2}$ 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. $0.40s$

Answer 1

The correct option is B $0.10s$

For interference to take place the wave should reflect back and come back to starting point where the second wave is starting

Distance travelled by first wave

$=2\times 0.4m$

$=0.8m$

Velocity of wave

$v=\sqrt{\frac{T}{\mu }}=\sqrt{\frac{T}{m/e}}$

$=\sqrt{1.6\times }0.4\times {10}^{-2}m/s$

$=8m/s$

$△T=\frac{distance}{speed}=\frac{0.8m}{8}=0.10sec$