A piece of wire of resistance 4 ohm is bent through 180 degree at its midpoint and its two halves are twisted together then the resistance is
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length of the wire = l
area of cross section of the wire = a
we know : R= p l/a
when the wire bent from its mid point and it's two halves twisted together,
length of the wire = l/2 (becomes half)
area of cross section = 2a (becomes double)
new resistance R' = p l/2/2a
R'/R =p l/2/2a÷ p l/a
=> pl/4a * a/pl = 1/4
put value of R = 4 ohm (given)
R'/R = 1/4
R'/4ohm = 1/4
R' = 4ohm / 4
R' = 1ohm
area of cross section of the wire = a
we know : R= p l/a
when the wire bent from its mid point and it's two halves twisted together,
length of the wire = l/2 (becomes half)
area of cross section = 2a (becomes double)
new resistance R' = p l/2/2a
R'/R =p l/2/2a÷ p l/a
=> pl/4a * a/pl = 1/4
put value of R = 4 ohm (given)
R'/R = 1/4
R'/4ohm = 1/4
R' = 4ohm / 4
R' = 1ohm
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