a wire of resistance 3 ohm and length 10 cm is stretched to length 30 cm assuming that is has a uniform cross section what will be its new resistance
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Initial length was 10 cm .
It became 30 cm .
So it was tripled .
Volume is always conserved .
Volume = area × length
If length is tripled then the area has to be one-third to conserv the volume .
Hence area become 1/3 rd .
By formula :
R = p l / a
= > R = p ( 3 l ) / ( 1 / 3 ) a
= > R = 9 p l / a
So resistance becomes 9 times the original .
Original resistance = 3 ohms.
So new resistance = 3 × 9 ohms
= > 27 ohms.
ANSWER:
27 ohms.
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