1.

A piece of wire of resistance R is cut into five equalparts. These parts are then connected in parallel.If the equivalent resistance of this combination isR', then the ratio R/R is(a) 1/251.(b) 1/5(c) 525CBSE 2012)

Answer»

when the piece of wire having resistance R is cut into 5 . then the resistance of each parts becomes R/5. due to the change in length from l to l/5.

now if the resistances are connected in parallel. the the resulting R' is 1/R' = 1/(R/5)+1/(R/5)+1/(R/5)+1/(R/5)+1/(R/5) => 1/R' = 5*(5/R) = 25/R => R' = R/25

so, the value of R/R' = 1/(1/25) = 25.



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