Chapter 6 · Class 11-12 & JEE/NEET

Current Electricity

68 topics in 16 parts

Full lessonClass 12 Physics · Current Electricity Practice380 practice questions

Key formulas

Drift Velocity & Current Relation
$I = n e A v_d, \quad v_d = \frac{e E \tau}{m} = \frac{e V \tau}{m l}$
Ohm's Law & Resistivity
$R = \rho \frac{l}{A}, \quad \rho = \frac{m}{n e^2 \tau}, \quad \vec{J} = \sigma \vec{E}$
Temperature Dependence
$R(T) = R_0 (1 + \alpha \Delta T), \quad \rho(T) = \rho_0 (1 + \alpha \Delta T)$
Balanced Wheatstone Bridge
$\frac{P}{Q} = \frac{R}{S} \implies I_G = 0 \text{ (Galvanometer null deflection)}$

Ohm's law Resistivity Joule's heating Electric power Electric Current Current Density

Key ideas

Wheatstone Bridge Circuit Network & Equipotential Reduction

4. Systematic Comparison & Parameter Classifications

Instrument	Working Principle	Ideal Internal Resistance	Circuit Connection
Ammeter	Measures Current (Shunt in parallel with coil)	Zero (R_A → 0)	Connected in SERIES
Voltmeter	Measures Potential Diff (High resistor in series)	Infinite (R_V → ∞)	Connected in PARALLEL
Potentiometer	Null-deflection method (No current drawn)	Infinite equivalent resistance	Measures true EMF without loading effect
Meter Bridge	Balanced Wheatstone bridge principle	N/A (Standard wire length 100 cm)	R/S = l / (100 - l)

Exam Worked Example

Problem: In a meter bridge experiment, the null point is obtained at 40 cm from the left end when a known resistance of 3 Ω is connected in the left gap. What is the unknown resistance in the right gap?

● Step 1: Formula for meter bridge is R / X = l / (100 - l), where l is the balance length from the left end.

● Step 2: Here R = 3 Ω, l = 40 cm, so (100 - l) = 60 cm.

● Step 3: 3 / X = 40 / 60 = 2 / 3.

● Step 4: Unknown resistance X = (3 * 3) / 2 = 4.5 Ω.

Checkpoint

1. Why is a potentiometer preferred over a standard voltmeter for measuring the EMF of an electrochemical cell?

All 68 topics in Current Electricity

Electric Current & Ohm's Law
- Charge Transport & Current Flow
- Time-Varying Current
- Ohm's Law Statement & Verification
- Validity & Failure of Ohm's Law
Drift Velocity & Mobility
- Conduction Model in Conductors
- Current Density & Charge Carrier Drift
- Relation Between Drift Velocity & Current
- Electron Mobility & Relaxation Time
- Ionic Conduction
Resistance & Resistivity
- Material Resistivity & Conductivity
- Dependence on Dimensions & Geometry
- Change in Resistance
- Nonuniform Conductor Geometries
- Resistor Colour Code
Temperature Coefficient of Resistivity
- Resistance Temperature Dependence
- Finding Coefficient of Resistance
- Coefficient of Resistance Calculations
- Composite Resistors
- Superconductivity
Electromotive Force & Internal Resistance
- EMF & Terminal Potential Difference
- Cell Losses & Terminal Voltage
- Charging of a Cell
Combination of Cells
- Series Grouping
- Parallel Grouping
- Mixed Grouping
- Grouping of Unequal Cells
Combination of Resistance
- Calculation of Effective Resistance
- Series & Parallel Network Reduction
- Current Divider Rule
- Voltage Divider Rule
- Short & Open Circuits
Equipotential Points
- Electrical Symmetry
- Path Symmetry
- Shifted Symmetry
- Method of Equipotential Reduction
Kirchhoff's Laws for Electrical Networks
- Current Law (KCL)
- Voltage Law (KVL)
- Guidelines for Network Analysis
Circuit Analysis
- General Circuit Solving
- Superposition Principle
- Nodal Analysis
- Thevenin's & Norton's Theorems
- Maximum Power Transfer Theorem
- Black-Box Networks
Balanced Wheatstone Bridge
- Balance Condition
- Unbalanced Bridge Analysis
- Non-Ohmic Bridge Elements
Meter Bridge
- Construction & Balance Condition
- Checking Connections & End Corrections
- Balance-Point Shift
- Experimental Errors & Sensitivity
Potentiometer
- Principle & Construction
- Comparison of EMFs
- Determination of Cell Internal Resistance
- Voltmeter & Ammeter Calibration
Galvanometer, Ammeter & Voltmeter
- Moving-Coil Mechanism & Sensitivity
- Conversion to Ammeter & Shunt Resistance
- Conversion to Voltmeter & Series Multiplier
- Instrument Loading Effects
Electrical Power & Heating Effects
- Resistor Power Dissipation
- Joule Heating & Electrical Energy
- Bulbs & Rated Power
- Transmission Losses & Fuses
RC Circuits
- DC Steady State in Capacitive Circuits
- Charging of a Capacitor
- Discharging of a Capacitor
- Time Constant Calculation
- Capacitive Circuit Energy & Heat