Wave Motion 5 Question 5

5. A string of length 0.4m and mass 102kg 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 Δt. The minimum value of Δt, which allows constructive interference between successive pulses, is

(1998, 2M)

(a) 0.05s

(b) 0.10s

(c) 0.20s

(d) 0.40s

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Answer:

Correct Answer: 5. (b)

Solution:

  1. Mass per unit length of the string,

m=1020.4=2.5×102kg/m

Velocity of wave in the string,

v=Tm=1.62.5×102v=8m/s

For constructive interference between successive pulses

Δtmin =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.)



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