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General Science · Class 10 · Chapter 8: Current Electricity

8 min

Key points

Electric current is the flow of electric charges through a conductor — measured in amperes (A)
Conventional current flows from positive to negative terminal, while electron flow is opposite
Ohm's Law states that current through a conductor is directly proportional to voltage and inversely proportional to resistance
Resistance depends on length, cross-sectional area, temperature and nature of material
In series circuits, current is same throughout but voltage divides across components
In parallel circuits, voltage is same across all branches but current divides
Electric power is the rate of doing electrical work — measured in watts
Electrical energy consumed is measured in kilowatt-hours (kWh) by KESC meters in Karachi homes
Fuses and circuit breakers protect electrical circuits from overloading and short circuits

Definitions

Electric Current: Electric current is the rate of flow of electric charge through any cross-section of a conductor. Its SI unit is ampere.
Resistance: Resistance is the property of a substance which opposes the flow of current through it. Its SI unit is ohm (Ω).
Ohm's Law: Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided the temperature remains constant.
Electric Power: Electric power is the rate of doing electrical work or the rate of consumption of electrical energy. Its SI unit is watt.
Electromotive Force (EMF): EMF is the energy per unit charge that is imparted to charges by the battery or generator. Its unit is volt.

Worked example

Define electric current. A current of 2A flows through a conductor for 5 minutes. Calculate the charge that flows through it. (4 marks)

Electric current is defined as the rate of flow of electric charge through a conductor. Given: I = 2A, t = 5 minutes = 300s. Using Q = I × t, Q = 2 × 300 = 600 coulombs.

Common mistakes

Students confuse conventional current direction with electron flow direction
Forgetting to write Ohm's Law formula before solving numerical problems
Mixing up series and parallel circuit properties — remember current same in series, voltage same in parallel
Not converting units properly in power calculations (kW to W, hours to seconds)
Drawing incorrect circuit diagrams without proper symbols for resistors, battery, and meters

Quick recap

Electric current is rate of flow of charge (I = Q/t). Ohm's law states V = IR for constant temperature. In series circuits, current is same everywhere but voltage divides. In parallel circuits, voltage is same but current divides.

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