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Question : 36
Total: 39
(a) (i) What is meant by resistance of a conductor? Define its SI unit.
(ii) List two factors on which the resistance of a rectangular conductor depends.
(iii) How will the resistance of a wire be affected if its
(1) length is doubled, and
(2) radius is also doubled?
Give justification for your answer.
OR
(b) In an electric circuit three bulbs of100 W
(i) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(ii) Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason for your answer.
(ii) List two factors on which the resistance of a rectangular conductor depends.
(iii) How will the resistance of a wire be affected if its
(1) length is doubled, and
(2) radius is also doubled?
Give justification for your answer.
OR
(b) In an electric circuit three bulbs of
(i) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(ii) Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason for your answer.
Solution:
(a) (i) Resistance is property of the conductor due to which it resists the flow of the electric current through it. It is the ratio of the potential difference across end to the current flowing. Its SI unit is ohm ( Ω )
(ii) The factor on which the resistance of a conductor depends;
(1) The temperature of the conductor,
(2) Length of the conductor,
(3) Resistivity of the conductor,
(4) Cross-sectional area of the conductor.
(iii) (1)R =
Where,ρ = l =
A =
Hence if the length is double then
⇒ R 1 = ρ
∴ R 1 = 2 ( R )
So, if the length of the resistance gets doubled then resistance also gets doubled.
(2) Now when the radius is double then
⇒ R 2 =
⇒ R 2 =
∴ R 2 =
( R )
So if the radius gets doubled then resistance will be
OR
R
In series:
Current in each bulb=
In Parallel:
Net current=
Current will get equally divided in three bulbs=
=
(i) No, the bulbs in the two circuits will not glow with the same brightness. The resistance in the parallel connection of resistors is always less than the resistance in the series connections. So, the bulbs in parallel connection will grow with more brightness.
(ii) If one bulb gets fused, the entire circuit will break in a series connection. So, no current will flow into the bulbs. All three bulbs will stop glowing in a series connection. In a parallel connection, the situation is different. Even if the bulb gets fused, the current will continue to flow into the other two bulbs. So, in parallel connection, the other two bulbs will continue to glow.
(ii) The factor on which the resistance of a conductor depends;
(1) The temperature of the conductor,
(2) Length of the conductor,
(3) Resistivity of the conductor,
(4) Cross-sectional area of the conductor.
(iii) (1)
Where,
Hence if the length is double then
So, if the length of the resistance gets doubled then resistance also gets doubled.
(2) Now when the radius is double then
So if the radius gets doubled then resistance will be
OR
Let us assume that resistance of each bulb is
In series:
Current in each bulb
In Parallel:
Net current
Current will get equally divided in three bulbs
(i) No, the bulbs in the two circuits will not glow with the same brightness. The resistance in the parallel connection of resistors is always less than the resistance in the series connections. So, the bulbs in parallel connection will grow with more brightness.
(ii) If one bulb gets fused, the entire circuit will break in a series connection. So, no current will flow into the bulbs. All three bulbs will stop glowing in a series connection. In a parallel connection, the situation is different. Even if the bulb gets fused, the current will continue to flow into the other two bulbs. So, in parallel connection, the other two bulbs will continue to glow.
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