Electricity is one of the most important forms of energy in modern life. Understanding how electric circuits work helps us design everything from simple torches to complex computers.
What is an Electric Circuit?
An electric circuit is a closed path through which electric current flows. For current to flow, the circuit must be complete (no gaps) and connected to a source of electrical energy.
Components of an Electric Circuit
- Cell / Battery – Source of electrical energy. A battery is two or more cells connected together.
- Switch – Opens (breaks) or closes (completes) a circuit.
- Bulb / Load – Converts electrical energy into light and heat.
- Wires – Conduct electricity; usually made of copper.
- Ammeter – Measures electric current (connected in series).
- Voltmeter – Measures voltage / potential difference (connected in parallel).
Electric Current
Electric current is the flow of electric charge through a conductor. It is measured in Amperes (A). Current flows from the positive terminal of a cell, through the external circuit, to the negative terminal.
Voltage (Potential Difference)
Voltage is the "push" that drives current through a circuit. It is measured in Volts (V). A higher voltage pushes more current through the same resistance.
Resistance
Resistance is the opposition to the flow of current. It is measured in Ohms (Ω). Materials with low resistance (copper, silver) are good conductors; those with high resistance (rubber, plastic) are insulators.
Ohm's Law
For a conductor at constant temperature:
V = I x R
Where V = voltage (volts), I = current (amperes), R = resistance (ohms).
Series and Parallel Circuits
- Series circuit – Components connected end to end in a single loop. The same current flows through all components. If one component fails, the whole circuit breaks.
- Parallel circuit – Components connected across the same two points (side by side). Each component has the same voltage across it. If one component fails, others continue to work.
Conductors and Insulators
- Conductors allow electricity to flow through them: copper, iron, aluminium, graphite.
- Insulators do not allow electricity to flow: rubber, plastic, wood, glass.
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A torch contains a battery (energy source), a bulb (load), a switch, and connecting wires. When the switch is closed, the circuit is complete, current flows, and the bulb lights up. Opening the switch breaks the circuit and the bulb goes off.
Using Ohm's Law: A bulb has a resistance of 10 Ω and is connected to a 5 V battery. Current = V / R = 5 / 10 = 0.5 A.
In a series circuit with two bulbs, if one bulb fuses (breaks), no current flows and both bulbs go off. This is why old Christmas lights wired in series all went off when one bulb blew.
In a parallel circuit with two bulbs, if one bulb fuses, current continues to flow through the other branch, so the second bulb remains lit. This is how household wiring is arranged.
A student tests whether water conducts electricity. Pure distilled water does not conduct electricity well, but salt water does because dissolved salt produces ions that carry charge. This shows that some liquids are conductors.
A voltmeter is connected across a bulb (in parallel) and reads 3 V. An ammeter in series reads 0.5 A. Resistance of bulb = V / I = 3 / 0.5 = 6 Ω.
Three identical bulbs in series with a 6 V battery: each bulb shares the voltage equally, so each gets 6/3 = 2 V. In parallel, each bulb receives the full 6 V, making them brighter.
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Key Formulas
Key formulas
Common mistakes
- Connecting an ammeter in parallel — it has very low resistance and will short-circuit; always connect in series.
- Thinking current is "used up" by components — current is the same throughout a series circuit; only energy (voltage) is "used."
Summary
An electric circuit needs a complete closed path, an energy source, and components (bulbs, switches). Current flows through conductors and is opposed by resistance. Ohm's Law (V = I x R) relates voltage, current, and resistance. Series circuits share current; parallel circuits share voltage, and are used in household wiring.