NTSE physics question In an experiment, it was observed that when the length of a wire in an electrical circuit is doubled, everything else remaining same, the current becomes half. On the other hand, if the thickness (diameter) of the wire is doubled, the current becomes 4 times. Two wires W1 and W2 of the same metal have the same current passing through them. The thickness of wire W2 is twice that of W1. Then the length of the wire W2 is 1. Sixteen times that of wire W1 2. Four times that of wire W1 3. Two times that of wire W1 4. Same as that of wire W1 Please explain! Thanks

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2015-10-10T02:59:45+05:30

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Resistance  R =  row * L / A    of a conductor.
       row  = resistivity of the material and is a constant.

since I = current = V / R, if length is doubled, then R is doubled, so current becomes half.

If thickness (R) is doubled, then  R becomes 1/4 th value.  So  the  current becomes 4 times. 

 Current in W1 = Current in W2

As thickness of W2 is 2 times that of W1, and length of W2 is  n times that of W1, then current in W2 will be  4 * I1 /n .

  since both currents are same,  n = 4. ie., length is 4 times that of W1.

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