7. Electric Circuits
Free study material · concepts, shortcuts & solved questions
An electric circuit is a closed, continuous path along which electric current can flow, typically consisting of a source of EMF (a cell or battery), connecting wires, a switch, and one or more devices such as bulbs, resistors, or motors. Circuit diagrams use standardised symbols so that circuits can be represented and communicated unambiguously without drawing realistic pictures of components.
Component | Standard Symbol Description |
|---|---|
Cell | A long thin line (positive terminal) next to a short thick line (negative terminal) |
Battery (multiple cells) | Several cell symbols placed in a row, connected in series |
Connecting wire (crossing, not joined) | Two lines crossing with no dot at the intersection |
Connecting wire (joined) | Two lines meeting at a dot |
Switch (open) | A break in the line with a lever not touching the other contact |
Switch (closed) | A break in the line with the lever touching, completing the path |
Resistor | A rectangle, or a zig-zag line |
Variable resistor / rheostat | A rectangle or zig-zag line with an arrow drawn across it |
Bulb / lamp | A circle with an X or filament loop inside it |
Ammeter | A circle with the letter A inside, connected in series |
Voltmeter | A circle with the letter V inside, connected in parallel |
Fuse | A small rectangle placed in series in the line, sometimes marked 'F' |
Earth / ground connection | A set of horizontal lines of decreasing length, or three diagonal lines |
Open, Closed, and Short Circuits
- Closed circuit: A circuit in which the path is complete and unbroken, so current flows continuously through it and connected devices operate normally.
- Open circuit: A circuit in which the path is broken at some point (for example, a switch is off, or a wire is disconnected/broken), so no current can flow and connected devices do not operate.
- Short circuit: A fault condition in which the live and neutral wires (or any two points at different potential) come into direct contact with each other through a path of very low resistance, bypassing the intended load. Since resistance is extremely low, an extremely large current flows suddenly (by Ohm's law, I = V/R, with R tending toward zero, I tends toward a very large value). This surge of current generates a great deal of heat very quickly and is a major cause of electrical fires; it is precisely what fuses and circuit breakers are designed to detect and interrupt.