Question

A rod of a certain metal is 1.0 m long and 0.6 cm in
diameter. Its resistance is 3.0 x 10-2 ohm. Another disc
made of the same metal is 2.0 cm in diameter and 1.0 mm
thick. What is the resistance between the round faces of
the disc?
(a) 1.35 x 10-8 ohm
(b) 2.70 x 10-7 ohm
(c) 4,05 x 10-6 ohm
(d) 8.10 x 10-5 ohm​

Answer 1

Answer:

b) is correct

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.