Question

A 10 ohm thick wire is drawn into a thin wire so that its length becomes three times . calculate its new resistance

Answer 1

Formula for resistance is as follows:

resistance(R) = restivity(r) x Length (L)/ Area (A)
 
R=rL/A

When the length increases by three, the cross section will reduce by three. Hence;
 the Length will be 3L
while area= A/3  
New resistance will be r3L/(A/3)  = r9L/A

If rL/A = 10ohms
Then 9(rL/A)= 10 x9 rL/A x(A/rL)  
                     =90

Therefore the new resistance = 90ohm

Answer 2

Answer:

90 ohm

Explanation:

L=3L

A=A/3

R=rl /A

r3L3/A=9rl/A

As per given rl/A=10ohm

9rl/A=9×10

=90ohm