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
Answers
Answered by
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.
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