Capacitors and Resistors

Definition

Two basic passive components of electric circuits: a resistor opposes the flow of current, while a capacitor stores electrical charge and energy.

Key points

• A resistor limits current; its opposition is called resistance, measured in ohms, and it converts electrical energy into heat (the principle behind heaters, electric irons, and incandescent bulbs).
• Ohm's law states that the current through a resistor is directly proportional to the voltage across it and inversely proportional to its resistance (voltage equals current times resistance).
• A capacitor stores charge on two conducting plates separated by an insulator (dielectric); its capacity is called capacitance, measured in farads.
• Capacitors are used to store energy briefly, smooth power supplies, in camera flashes, and in tuning circuits; resistors are used to control current and divide voltage.
• In series, resistances add up; capacitances add when capacitors are in parallel, the opposite pattern, which is a common testing point.

Why it matters for CAPF

Resistance in ohms and Ohm's law, the resistor as a heat producer, and the capacitor as a charge store are standard physics facts, and the series-parallel behaviour is a frequent conceptual question.

Common confusion

A resistor opposes current and dissipates energy as heat, while a capacitor stores energy and does not dissipate it; do not treat them as similar. Resistances add in series, but capacitances add in parallel, which reverses the usual intuition.

Related concepts

concept electromagnetic induction, concept semiconductor devices, concept superconductors

Parent note

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