Question

 Show all the solutions. Round off answers to two decimal places. Be consistent with the units.

4. A 40-ohm resistor is to be wound from 0.0001 cm² platinum wire. How many meters of wire are needed? (Refer to the table of resistivities under the theory for the value of resistivity of  platinum)

5. A silver wire 2 m long is to have a resistance of 0.5 ohm. What should be its

 cross-sectional area? (Refer to the table of resistivities under the theory for the value of resistivity of silver)

Answer 1

Answer

4.

Resistance is given by

$R=\rho \frac{l}{A}$

$40=(1.06\times 10^{-7})\frac{l}{10^{-8}}\\l=3.77m$

5.

$R=\rho \frac{l}{A}$

So

$0.5=(1.59\times10^{-9})\frac{(2)}{A}\\A=6.36\times10^{-9}m^2$