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What is an electric circuit, and what are its components?

Class 7 ScienceNCERT chapter: Electricity: Circuits and their Componentsइसे हिंदी में पढ़ें

Exam-ready answer

An electric circuit is a complete, closed path along which electric current flows from the positive terminal of a cell, through the devices, back to its negative terminal. Its main components are an electric cell or battery (the source), connecting wires, a switch to open or close the path, and a device such as a bulb or LED.

Explanation

Connect a torch bulb to an electric cell with two wires, one from each terminal of the cell to the two terminals of the bulb. The bulb glows only when the path is complete. If any wire is loose or removed, the bulb stops glowing. A complete path is called a closed circuit, and a broken path is called an open circuit; current flows only in a closed circuit.

Each component has a job. The electric cell is the source of electrical energy; it has a positive terminal (+, the metal cap) and a negative terminal (−, the flat metal disc). Two or more cells joined so that the positive terminal of one touches the negative terminal of the next form a battery. Connecting wires carry the current, and a switch makes or breaks the circuit to turn a device on or off.

Inside a torch bulb is a thin wire called the filament, which glows when current passes through it. An LED also glows, but only if it is connected the right way round: its longer leg goes to the positive terminal. Because drawing real cells and bulbs takes time, standard symbols are used for each component. A drawing of a circuit made with these symbols is called a circuit diagram.

Points to remember

  1. Electric circuit: a closed path along which electric current flows.
  2. Components: electric cell or battery, connecting wires, switch, and a device such as a bulb or LED.
  3. Current flows from the positive terminal of the cell, through the circuit, to its negative terminal.
  4. Closed circuit — path complete, bulb glows; open circuit — path broken, no current, bulb does not glow.
  5. Circuit diagram: a drawing of a circuit using standard symbols for its components.

Exam tip

Draw a neat circuit diagram using standard symbols for the cell, switch and bulb, mark the + and − terminals of the cell, and show the direction of current with an arrow.

Questions students also ask

What is the difference between an open and a closed circuit?
In a closed circuit, the path from the positive to the negative terminal of the cell is complete, so current flows and the bulb glows. In an open circuit, the path is broken somewhere, for example by a switch in the off position, so no current flows.
Why does a fused bulb not glow even in a closed circuit?
When a bulb fuses, its filament breaks. The path for current through the bulb is no longer complete, so the circuit becomes open at that point. No current flows, and the bulb does not glow.
What does a switch do in a circuit?
A switch is a simple device that either completes or breaks the circuit. In the on position it closes the gap so that current flows; in the off position it opens the gap and the current stops, turning the device off.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.