Question:

A wave y=asin⁡(ωt−kx) on a string meets with another wave producing a node at x=0. Then the equation of the unknown wave is:

Updated On: Mar 25, 2026
  • (A) y=asin⁡(ωt+kx)
  • (B) y=−asin⁡(ωt+kx)
  • (C) y=asin⁡(ωt−kx)
  • (D) y=−asin⁡(ωt−kx)
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The Correct Option is B

Solution and Explanation

Explanation:
Given:Equation of wave, y=asin⁡(ωt−kx)......(i)Since the coefficient of x is negative in the above wave equation, it suggests that the wave is traveling in a positive x direction. The other wave must travel in the opposite direction to form a node.Let the two possible equations of waves travelling in negative direction bey1=asin⁡(ωt+kx)......(ii)andy2=−asin⁡(ωt+kx).......(iii)Using the propertysin⁡(A+B)+sin⁡(A−B)=2sin⁡Acos⁡BIf waves (i) and (ii) superimpose, the net displacement isy3=(y+y1)=2asin⁡(ωt)cos⁡(kx)Similarly,sin⁡(A−B)−sin⁡(A+B)=−2sin⁡Bcos⁡ASo, if waves (i) and (iii) superimpose the net displacement isy3=(y+y2)=−2asin⁡(kx)cos⁡(ωt)Since at node, displacement y3=0 soy3=0=−2asin⁡(kx)cos⁡(ωt)⇒sin⁡(kx)=0 ⇒x=0Therefore, eq. (iii) satisfies the property of a node at x=0.So, the equation of the unknown wave isy=−asin⁡(ωt+kx)Hence, the correct option is (B).
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