A wire of silver has a resistance of 1 ohm. Specific resistance of constantan is 30 times the specific resistance of silver. Find the resistance of a constantan wire whose length is one third length of the silver wire and radius half the radius of the silver wire.

Explanation

we know that `R=(rhol)/(A)=(rhol)/(pir^(2))`
`(R_(c))/(R_(s))=(rho_(c))/(rho_(s))(l_(c))/(l_(s))=(r_(s)^(2))/(r_(c)^(2))=(30)/(3)xx4=40`
Resistance of constantan `R_(c)=40xx1=40Omega`.