Question

A rod of certain metal is 1 m long and
0.6 cm in diameter. Its resistance is
3x10-3. A disc of the same metal is 1
mm thick and 2 cm in diameter, what is
the resistance between it's circular
faces.​

Answer 1

Answer:

Explanation:

As, R=ρl/A=ρl/(πd  2 /4)

Resistance for a given material is directly proportional to the length and inversely proportional to the square of diameter of round faces.

So for the second rod, diameter is 2.0/0.6=10/3 times diameter of the first one.

and, length is 1.0mm/1m=1/1000 times the length of first one.

Thus resistance of the second rod is,  

(10/3)  2

 1/1000  =9×10  −5

 times the resistance of the first one.

So resistance of the second rod is 3×10  −3  ×9×10  −5  =2.70×10  −7  Ω

Option B is correct.