Current Electricity

What you'll learn

A friendly, first-principles walk through Current Electricity for CBSE Class 12 — electric current, Ohm's law, resistivity, series and parallel resistors, Kirchhoff's rules and the Wheatstone bridge — with everyday analogies, correct SI units, and a fully worked numerical.

This chapter has

Current Electricity — solved practice questions

8 Class 12 Physics questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   The resistance of a conductor is 10 ohm and the potential difference across it is 5 V. The current through it is

   • A2 A
   • B0.5 A
   • C50 A
   • D5 A
   Show answer & solution

   Correct answer: (B) 0.5 A

   By Ohm's law I = V/R = 5/10 = 0.5 A.

2. Q2easy

   The drift velocity of free electrons in a conductor is directly proportional to

   • Athe square of the applied electric field
   • Bthe cross-sectional area of the conductor
   • Cthe number density of electrons
   • Dthe applied electric field
   Show answer & solution

   Correct answer: (D) the applied electric field

   Drift velocity v_d = eE tau/m, so v_d is directly proportional to the applied electric field E.

3. Q3easy

   The SI unit of electrical resistivity is

   • Aohm metre (ohm m)
   • Bohm per metre (ohm m^-1)
   • Cohm (ohm)
   • Dsiemens (S)
   Show answer & solution

   Correct answer: (A) ohm metre (ohm m)

   From rho = R A / L, resistivity has units of ohm x metre (ohm m).

4. Q4easy

   Three resistors of 2 ohm, 3 ohm and 5 ohm are connected in series. Their equivalent resistance is

   • A0.97 ohm
   • B3.33 ohm
   • C10 ohm
   • D30 ohm
   Show answer & solution

   Correct answer: (C) 10 ohm

   In series resistances add: R = 2 + 3 + 5 = 10 ohm.

5. Q5medium

   Two resistors of 6 ohm and 3 ohm are connected in parallel. The equivalent resistance is

   • A9 ohm
   • B2 ohm
   • C4.5 ohm
   • D18 ohm
   Show answer & solution

   Correct answer: (B) 2 ohm

   For parallel, R = (R1 R2)/(R1 + R2) = (6 x 3)/(6 + 3) = 18/9 = 2 ohm.

6. Q6medium

   A cell of emf 2 V and internal resistance 0.5 ohm is connected to an external resistance of 1.5 ohm. The current in the circuit is

   • A0.5 A
   • B1.33 A
   • C4 A
   • D1 A
   Show answer & solution

   Correct answer: (D) 1 A

   I = E/(R + r) = 2/(1.5 + 0.5) = 2/2 = 1 A.

7. Q7medium

   An electric bulb is rated 60 W at 220 V. The resistance of its filament is approximately

   • A807 ohm
   • B3.67 ohm
   • C220 ohm
   • D13200 ohm
   Show answer & solution

   Correct answer: (A) 807 ohm

   R = V^2/P = (220)^2/60 = 48400/60 = 807 ohm approximately.

8. Q8medium

   Kirchhoff's junction rule (current rule) is based on the conservation of

   • Aenergy
   • Bmomentum
   • Ccharge
   • Dmass
   Show answer & solution

   Correct answer: (C) charge

   The junction rule states that total current entering a junction equals total current leaving it, which is a statement of conservation of charge.

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