🔬 ScienceGrade 3Lesson 20
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Simple Electric Circuits

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Learning Objectives

  • 1Name the key components of a simple electric circuit
  • 2Explain the role of each component in allowing current to flow
  • 3Distinguish between an open circuit and a closed circuit
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Mini Lesson

Electricity flows through a path called a circuit. A simple circuit has four key components: a battery (power source), wires (path), a switch (control), and a bulb (output). For electricity to flow, the circuit must be a complete, unbroken loop — a closed circuit.

Components of a Simple Circuit

  1. Battery — stores chemical energy and converts it into electrical energy to power the circuit.
  2. Wire — a metal conductor that carries the electric current from one component to the next.
  3. Switch — opens or closes the circuit. Open switch = no current flows. Closed switch = current flows.
  4. Bulb — converts electrical energy into light (and a little heat) when current passes through its filament.
  5. Closed circuit — the complete loop is formed; current flows and the bulb lights up.

Open vs Closed Circuit

  • Open circuit: the loop is broken (e.g. switch is open). Current cannot flow, so the bulb is OFF.
  • Closed circuit: the loop is complete. Current flows from battery, through wire, switch, and bulb, and back to battery. Bulb is ON.
  • A break anywhere in the circuit stops the current — even a loose wire will turn off the bulb.
Simple circuit component sequenceFive boxes in sequence: Battery, Wire, Switch, Bulb, Closed Circuit, connected by arrows.Simple Electric Circuit1BatteryPower2WirePath3SwitchOn/Off4BulbLight5CircuitClosedSwitch open = no current (bulb OFF)Switch closed = current flows (bulb ON)
Open vs closed circuit comparisonLeft: open circuit with switch open and bulb off. Right: closed circuit with switch closed and bulb glowing.Open vs Closed CircuitOpen CircuitBat.OFFGap — no currentBulb is OFFClosed CircuitBat.ONLoop completeBulb is ON
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Think of the circuit like a running track. The runners (electrons) can only run if the track is a complete loop. Any gap stops them completely.

Vocabulary
Circuit
A complete, closed path through which electric current flowse.g. A simple circuit powers a flashlight bulb.
Battery
A device that stores chemical energy and converts it to electrical energye.g. A 1.5V battery powers a small flashlight.
Conductor
A material that allows electric current to pass through it easilye.g. Copper wire is a good conductor.
Switch
A device that opens or closes a circuit to control the flow of currente.g. Flipping a switch turns a light on or off.
Open circuit
A circuit with a gap or break so no current flowse.g. An open switch creates an open circuit.
Closed circuit
A complete, unbroken circuit through which current can flowe.g. Closing the switch completes the circuit.
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