A rheostat has 100 turns of a wire of radius 0 . 4 mm having resistivity 4.2 × 10 − 7 Ωm . The diameter of each turn is 3 cm . What is the maximum value of resistance that it can introduce?

Given that, Number of turns on Rheostat is 100 , radius of the wire is 0 . 4 mm Resistivity of the material, ρ = 4.2 × 10 − 7 Ωm Diameter of each turn is 3 cm Length of the wire used l = n π D = 100 π D Expression for resistance of the wire is R = ρ l π r 2 R = ρ l π r 2 = ρ 100 π D π r 2 = 100 ρ D r 2 R = 100 × 4.2 × 10 − 7 × 3 × 10 − 2 0.4 × 10 − 3 2 = 7.875 Ω

EASY

12th CBSE

IMPORTANT

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A wire of resistance $5 Ω$ is uniformly stretched until its new length becomes $4$ times the original length. Find its new resistance.

Important Questions on Current Electricity

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 11

A metallic wire of length

1 m

is stretched to double its length. Calculate the ratio of its initial and final resistances assuming that there is no change in its density on stretching.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 12

A wire of certain radius is stretched so that its radius decreases by a factor

n

. Calculate its new resistance.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 13

A wire

1 m

long and

0.13 mm

in diameter has a resistance of

4.2 Ω

. Calculate the resistance of another wire of the same material whose length is

1.5 m

and diameter

0.155 mm

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 14

A rheostat has

100

turns of a wire of radius

0.4 mm

having resistivity

4.2 \times 10^{- 7} Ωm

. The diameter of each turn is

3 cm

. What is the maximum value of resistance that it can introduce?

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 15

Given that resistivity of copper is

1.68 \times 10^{- 8} Ωm

. Calculate the amount of copper required to draw a wire

10 km

long having resistance of

10 Ω

. The density of copper is

8.9 \times 10^{3} kg m^{- 3}

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 16

The size of a carbon block is

1.0 cm \times 1.0 cm \times 50 cm

. Find its resistance (i) between the opposite square faces (ii) between the opposite rectangular faces of the block. The resistivity of carbon is

3.5 \times 10^{- 5} Ω cm

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 17

Two wires

A

and

B

of the same material have their lengths in the ratio

1 : 5

and diameters in the ratio

3 : 2

. If the resistance of the wire

B

180 Ω

, find the resistance of the wire

A

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 3 - Current Electricity>Problems For Practice>Q 18

A uniform wire is cut into four segments. Each segment is twice as long as the earlier segment. If the shortest segment has a resistance of

4 Ω

, find the resistance of the original wire.

A wire of resistance 5 Ω is uniformly stretched until its new length becomes 4 times the original length. Find its new resistance.

Important Questions on Current Electricity

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A wire of resistance $5 Ω$ is uniformly stretched until its new length becomes $4$ times the original length. Find its new resistance.