Current Electricity

Q.1

. The sequence of bands marked on a carbon resistor is red, red. Red silver. What is the value of

resistance?

Ans:‐ 22×102 ±10%

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Q.2 Does the drift velocity vary with the magnitude of the current through the conductor?

Explain.

Ans. Yes. Drift velocity,

Q.3 . A wire is cut into half. What is the effect on its specific resistance?

Ans :‐ No effect.

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Q.4 :‐ Why do we prefer a potentiometer with a longer bridge wire?

Ans:‐ When the bridge wire is longer the potential gradient is smaller. Smaller the potential

gradient more is the sensitivity of potentiometer wire.

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Q.5 What are the factors affecting internal resistance of a cell

Ans-Nature of electrolyte

Separation between the electrode

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Q.6 Establish a relation between the current and drift velocity

Ans‐Page 97 NCERT

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Q.7 Describe with the help of circuit diagram how a potentiometer can be used to compare the

e.m.f. of two cells.

Ans-Potential gradient – The potential drop per unit of length of the potentiometer.

Method to compare emf of two cells –

Q.8

Define resistivity and state its SI unit. State and explain how the resistivity of a conductor varies

with temperature

Ans-Resistivity is the resistance of a conductor of that material having unit length and unit area of

cross-section.

S.I. unit = ohm metre (Ω M)

Resistivity = ↑

With increase in temperature, the electrons suffer collisions more frequently and the relaxation

time τ decreases. Hence, the resistivity of a conductor increases.

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Q.9

(a) Three resistors 1 Ω, 2 Ω, and 3 Ω are combined in series. What is the total

resistance of the combination? (b) If the combination is connected to a battery of

emf 12 V and negligible internal resistance, obtain the potential drop across each

resistor

Ans-

(a) Three resistors of resistances 1 Ω, 2 Ω, and 3 Ω are combined in series. Total resistance of

the combination is given by the algebraic sum of individual resistances.

Total resistance = 1 + 2 + 3 = 6 Ω

(b) Current flowing through the circuit = I

Emf of the battery, E = 12 V

Total resistance of the circuit, R = 6 Ω

The relation for current using Ohm’s law is,

Potential drop across 1 Ω resistor = V1

From Ohm’s law, the value of V1 can be obtained as

V1= 2 × 1= 2 V … (i)

Potential drop across 2 Ω resistor = V 2

Again, from Ohm’s law, the value of V2 can be obtained as

V2= 2 × 2= 4 V … (ii)

Potential drop across 3 Ω resistor = V 3

Again, from Ohm’s law, the value of V3 can be obtained as

V3= 2 × 3= 6 V … (iii)

Therefore, the potential drop across 1 Ω, 2 Ω, and 3 Ω resistors are 2 V, 4 V, and 6 V

respectively.

Q.10 Derive the balance condition of Wheat Stone bridge .also draw the circuit diagram to find the

specific rsistance by meter bridge.

Ans‐

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