A string of length 0.4 m and mass 10−2 kg is tightly clampled at its ends. The tension in the string is 1.6 N. identical wave pulses are produced at one end at equal intervals of time ∆t. The minimum value of ∆t, which allows constructive interference between succesive pulses, is :
0.10 s
Mass per unit length of the string,
m=10−20.4=2.5×10−2 kg/m
∴ Velocity of wave in the string.
v=√Tm=√1.62.5×10−2
v=8 m/s
For constructive interference between successive pulses:
△tmin=2lv=(2)(0.4)8=0.10s
(After two reflections, the wave pulse is in same phase as it was produced, since in one reflection its phase changes by π and if at this moment next identical pulse is produced, then constructive interference will be obtained.)