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ICSE Class 10 · Physics · Chapter 8

Current Electricity

6 topics · 15 questions

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Electric Current

Electric Current: The rate of flow of electric charge through a conductor. I = Q/t.
SI Unit: Ampere (A). 1 Ampere = 1 Coulomb/second.
Direction: Conventional current flows from positive to negative terminal; electron flow is opposite.
Conductors and Insulators: Conductors allow current flow (metals); insulators resist it (rubber, plastic).
Ammeter: Device to measure current, connected in series.

Electric Potential and Potential Difference

Electric Potential: Work done per unit charge in bringing a charge from infinity to that point.
Potential Difference (V): Work done in moving unit charge between two points. V = W/Q.
SI Unit: Volt (V). 1 Volt = 1 Joule/Coulomb.
Voltmeter: Device to measure potential difference, connected in parallel.
EMF (Electromotive Force): Potential difference across a cell when no current flows.

Ohm's Law

Statement: Current through a conductor is directly proportional to potential difference across it, at constant temperature.
Formula: V = IR, where V = voltage, I = current, R = resistance.
Ohmic Conductors: Conductors that obey Ohm's law (metals at constant temperature).
Non-Ohmic Conductors: Do not obey Ohm's law (diodes, transistors, electrolytes).
Graph: V-I graph for ohmic conductor is a straight line through origin.

Resistance

Resistance: Opposition to flow of current. R = V/I.
SI Unit: Ohm (Ω). 1 Ω = 1 Volt/Ampere.
Factors Affecting Resistance: Length (R ∝ l), area of cross-section (R ∝ 1/A), material (resistivity ρ), and temperature.
Formula: R = ρl/A, where ρ = resistivity.
Resistivity: Property of material. Unit: Ω·m.
Conductance: Reciprocal of resistance. Unit: Siemens (S) or mho.

Combination of Resistors

Series Connection: R_total = R₁ + R₂ + R₃ + ... Current same, voltage divides.
Parallel Connection: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ... Voltage same, current divides.
Series Advantage: Increases total resistance.
Parallel Advantage: Decreases total resistance, provides multiple paths for current.
Applications: Christmas lights (series), household appliances (parallel).

Heating Effect of Current

Joule's Law: Heat produced H = I²Rt = VIt = V²t/R.
Unit: Joule (J) or calorie.
Applications: Electric heater, electric iron, electric bulb, fuse wire.
Fuse: Safety device that melts when excess current flows, breaking the circuit.
Power: P = VI = I²R = V²/R. Unit: Watt (W).

Formulas

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Formula 01

Current: I = Q/t

Charge per unit time

Formula 02

Potential Difference: V = W/Q

Work done per unit charge

Formula 03

Ohm's Law: V = IR

Relation between voltage, current, and resistance

Formula 04

Resistance: R = ρl/A

Depends on length, area, and resistivity

Formula 05

Series: R_total = R₁ + R₂ + R₃

Total resistance in series

Formula 06

Parallel: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃

Total resistance in parallel

Formula 07

Heat: H = I²Rt = VIt

Joule's law of heating

Formula 08

Power: P = VI = I²R = V²/R

Electrical power