Current Electricity
ICSE Grade 10 Physics - Chapter 8
📚 Smart Summary
1. 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.
2. 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.
3. 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.
4. 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.
5. 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).
6. 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
Charge per unit time
Work done per unit charge
Relation between voltage, current, and resistance
Depends on length, area, and resistivity
Total resistance in series
Total resistance in parallel
Joule's law of heating
Electrical power
🎯 Test Your Knowledge
Multiple Choice Questions
1. The SI unit of electric current is:
Knowledge2. Ohm's law states that:
Knowledge3. The SI unit of resistance is:
Knowledge4. An ammeter is connected in:
Knowledge5. A voltmeter is connected in:
Knowledge6. When resistors are connected in series, the total resistance:
Comprehension7. The resistance of a wire is directly proportional to:
Knowledge8. The heat produced in a resistor carrying current I for time t is:
Knowledge9. Assertion (A): Household appliances are connected in parallel. Reason (R): In parallel connection, each appliance gets the same voltage.
Assertion-Reasoning10. A fuse wire is made of material with:
KnowledgePractice Numericals
Practice Problem 1: A current of 2 A flows through a resistor of 10 Ω. Calculate the voltage across it (in V).
ApplicationPractice Problem 2: Three resistors of 5 Ω, 10 Ω, and 15 Ω are connected in series. Find the total resistance (in Ω).
ApplicationPractice Problem 3: Two resistors of 6 Ω each are connected in parallel. Find the equivalent resistance (in Ω).
ApplicationPractice Problem 4: A heater of resistance 20 Ω carries a current of 5 A for 10 minutes. Calculate the heat produced (in kJ).
ApplicationPractice Problem 5: An electric bulb is rated 100 W, 220 V. Calculate its resistance (in Ω).
Application