1.

the wire of length L and cross sectional area a is stretched to double its length find its new resistance

Answer»

Given old AREA of crossection = a
old length= l
now wire stretched length become 2l and rho be resistivity of material
since
New volume = old volume
new area of crossection * new length = old area of crossection * old length
=> new area of crossection = a*l/2l
= a/2
old RESISTANCE (r) = rho l/a
new resistance = rho 2l/(a/2)
= 4 rho *l/a
= 4r
thus new resistance become 4 TIMES of old resistance


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