A string of length 0.4 m and mass 10−2 kg is tightly clamped 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 Δt. The minimum value of Δt which allows constructive interference between successive pulses is

For string,  MassLength=m=10−20.4=2.5×10−2kg/m∴ Velocity  v=Tm=162.5×10−2=8m/sFor constructive interference between successive pulses.       Δtmin=2lv=2(0.4)8=0.1sec(After two reflections, the wave pulse is in same phase as it was produced since in one reflection it’s phase changes by π, and If at this moment next identical pulse is produced, then  constructive interference will be obtained.