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JEE Main 20178 AprilOnline
Exam
JEE Main
Year
2017
Date
8 April
Mode
Online
Subject
Physics
Chapter
Waves and Sound

JEE Main 2017 · 8 April · Online · Physics · Waves and Sound

Two wires W _ 1 and W _ 2 have the same radius r and respective,...

Two wires W1{W}_{1} and W2{W}_{2} have the same radius rrand respective, densities ρ1{ρ}_{1} and ρ2{ρ}_{2}, such that ρ2=4ρ1{ρ}_{2} = 4{ρ}_{1} . They are joined together at the point OO, as shown in the figure. The combination is used as a sonometer wire and kept under tension TT. The point OO is midway between the two bridges. When a stationary wave is set up in the composite wire, the joint is found to be a node. The ratio of the number of antinodes formed in W1{W}_{1} to W2{W}_{2} is

Two wires W _ 1 and W _ 2 have the same radius r and respective, densities ρ _ 1 and ρ _ 2 , such that ρ _ 2 = 4 ρ _ 1

Options

  1. A4:14: 1
  2. B1:21: 2
  3. C1:11: 1
  4. D1:31: 3

Correct answer

B. 1:21: 2

Step-by-step solution

Let p1{p}_{1} and p2{p}_{2} be the number of antinodes of both wires.

Fundamental frequency remains the same for both wires.

n1=n2{n}_{1} = {n}_{2}

T→sameT \to same

r→samer \to same

l→samel \to same

n=p2lTπr2ρn = \dfrac{p}{2l}\sqrt{\dfrac{T}{\pi{r}^{2}ρ}}

From the above equation, we have
p1ρ1=p2ρ2\dfrac{{p}_{1}}{\sqrt{{ρ}_{1}}} = \dfrac{{p}_{2}}{\sqrt{{ρ}_{2}}}

→p1p2=ρ1ρ2\to \dfrac{{p}_{1}}{{p}_{2}} = \sqrt{\dfrac{{ρ}_{1}}{{ρ}_{2}}}

The ratio of antinodes is p1p2=12\dfrac{{p}_{1}}{{p}_{2}} = \dfrac{1}{2}.

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