Wave motionHardBloom L3

Question

A wave travels on a light string. The equation of the wave is Y=Asin(kx−wt+30°) .It is reflected from a heavy string tied to an end of the light string at x=0.If 64% of the incident energy is reflected the equation of the reflected wave is

Options

A.Y=0.8Asin(kx−wt+30°+180°)
B.Y=0.8Asin(kx+wt+30°+180°)
C.Y=0.8Asin(kx+wt−30°)
D.Y=0.8Asin(kx+wt+30°)

Solution

Sol. Y = Asin(kx – ωτ + 30°)

Reflected wave will have opposite phase because it is reflected back from rigid end.

It will travel towards –ve x axis.

Ereff= 64% of initial energy

E ∝ A2

Y = A sin (kx – ωτ + 30°)

At x = 0

Y = A sin(–ωt + 30°)

Y = Asin(ωt + 150°)

Yref = (0.8A) sin(kx + ωτ + 150° + 180°)

= 0.8 A sin(kx + ωt + 330°)

= 0.8 A sin(kx + ωτ – 30°)

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