The following table gives the resistivity of three samples: Sample Resistivity A 1 . 6 × 10 - 8 Ω m B 5 . 1 × 10 - 8 Ω m C 10 . 6 × 10 - 6 Ω m Which of them is suitable for heating elements of electrical appliances and why?

Sample C because it has the highest resistivity in the given range of resistors. Note: Sample C has highest resistivity and consequently highest resistance. Therefore, it will resist the flow of charges more, and lead to development of heat faster.

A negligibly small current is passed through a wire of length 15 m and uniform cross-section 6.0 × 10 - 7 m 2 , and its resistance is measured to be 5.0 Ω . What is the resistivity of the material at the temperature of the experiment?

Given, Length of the wire, l = 15 m . Area of a cross-section of the wire, A = 6.0 × 10 - 7 m 2 . The resistance of the wire's material, R = 5.0 Ω . Say, ρ is the resistivity of the material. Resistance is related to the resistivity as, R = ρ l A ⇒ ρ = R A l ⇒ ρ = 5 × 6 × 10 - 7 15 = 2 × 10 - 7 Ω m ∴ The resistivity of the material is 2 × 10 - 7 Ω m .

The resistance of a nichrome wire at 0 o C is 10 Ω . If temperature coefficient of resistance is 0 . 004 / C o , find its resistance at boiling point of water.

Given, The resistance at, T 0 = 0 ° C , is R 0 = 10 Ω The coefficient of resistance, α = 0 . 004 / ° C Say, the resistance at, T 1 = 100 ° C is R 1 We know that the relation between the resistance, the temperature coefficient and the temperature is given by, R 1 = R 0 ( 1 + α t ) ⇒ R 1 = 10 ( 1 + 0 . 004 × 100 ) ⇒ R 1 = 14 Ω

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Two plates $R$ and $S$ are in the form of a square and have the same thickness. A side of $S$ is twice the side of $R$ Compare their resistances. The direction of current is shown by an arrow head figure.

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Important Questions on Current Electricity

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12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 3

The length of a conductor is doubled and its radius is halved, its specific resistance is

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12th Tamil Nadu Board

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 4

The specific resistance of copper, constantan and silver are

1.78 \times 10^{- 8}, 39.1 \times 10^{- 8}

and

10^{- 8} Ωm

respectively. Which of these is the best conductor of heat and electricity?

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12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 5

Write an expression for the resistivity of a substance.

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12th Tamil Nadu Board

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Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 6

The following table gives the resistivity of three samples:

Sample	Resistivity
$A$	$1.6 \times 10^{- 8} Ω m$
$B$	$5.1 \times 10^{- 8} Ω m$
$C$	$10.6 \times 10^{- 6} Ω m$

Which of them is suitable for heating elements of electrical appliances and why?

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12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 7

The storage battery of a car has an emf of

12 V

. If the internal resistance of the battery is

0.4 Ω

, what is the maximum current that can be drawn from the battery?

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12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 8

A negligibly small current is passed through a wire of length

15 m

and uniform cross-section

6.0 \times 10^{- 7} m^{2}

, and its resistance is measured to be

5.0 Ω

. What is the resistivity of the material at the temperature of the experiment?

HARD

12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 9

Two wires of equal length, one of aluminium and the other of copper, have the same resistance. Which of the two wires is lighter? Hence explain why aluminium wires are preferred for overhead power cables (

ρ_{A l} = 2.63 \times 10^{- 8} Ω m

ρ_{C u} = 1.72 \times 10^{- 8} Ω m

, Relative density of

A l = 2.7

, of

C u = 8.9

)

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12th Tamil Nadu Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 2 - Current Electricity>Exercise>Q 10

If a wire of length $1 m$ and resistance $10 Ω$ is stretched until its length becomes $3 m$ . What is its new resistance?

Two plates R and S are in the form of a square and have the same thickness. A side of S is twice the side of R Compare their resistances. The direction of current is shown by an arrow head figure.

Important Questions on Current Electricity

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Two plates $R$ and $S$ are in the form of a square and have the same thickness. A side of $S$ is twice the side of $R$ Compare their resistances. The direction of current is shown by an arrow head figure.