Physics-
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Question

Two wires of equal cross-section but one made of steel and the other of copper are joined end to end. When the combination is kept under tension, the elongations in the two wires are found to be equal. What is the ratio of the lengths of the two wires? (Given : steel = 2 cross times 10 to the power of 11 end exponent N m to the power of negative 2 end exponent right parenthesis

  1. 2 : 11    
  2. 11 : 2    
  3. 20 : 11    
  4. 11 : 20    

The correct answer is: 20 : 11


    Y equals fraction numerator s t r e s s over denominator s t r a i n end fraction blank o r blank s t r a i n equals fraction numerator s t r e s s over denominator Y end fraction o r fraction numerator increment L over denominator L end fraction equals fraction numerator s t r e s s over denominator Y end fraction
    Since, cross-sections are equal and same tension exists in both the wires, therefore, the stresses developed are equal.
    Also, increment L is given to be the same for both the wires.
    therefore blank L blank proportional to Y
    therefore blank fraction numerator L subscript s end subscript over denominator L subscript C u end subscript end fraction equals blank fraction numerator 2 blank cross times 10 to the power of 11 end exponent over denominator 1.1 blank cross times 10 to the power of 11 end exponent end fraction equals fraction numerator 20 over denominator 11 end fraction

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