Question

two wires a and b of the same material have their lengths in ratio 1:5 and diameter in ratio 3:2 . if the resistance of wire b is 180 ohms , find the resistance of wire a

Answer 1

Answer:

resistance R α length/area

Resistance = (density *length) /area

Let R1 &R2 be the resistances in first and second cases respectively

In the first case :

Length of the wire l1=l

Area of cross section of the wire A1=A

In the second case:

Length of the wire =l2=2l

Area of cross section of wire =A2=A1/2=A/4

Now assuming the density of the material is same in both the cases

Ratio of resistances R1/R2=l1A1/l2A2

=LA/2L(A/4)

=4LA/2LA

=2:1

Explanation: