Electric Circuits: quick revision, 13 bites

The Complete Circuit

Current needs a complete path.

An **electrical circuit** is a setup that provides a **complete path** for electric current to flow. The lamp glows only when one terminal of the lamp is connected to one terminal of the cell and the other terminal of the lamp is connected to the other terminal of the cell. This creates a closed loop for the current.

Takeaway. A lamp glows only when it is part of a complete, unbroken circuit.

Electric Cell and Its Terminals

The portable source of power.

An **electric cell** is a portable source of electrical energy. All electric cells have two **terminals**: a **positive (+ve)** terminal and a **negative (-ve)** terminal. In a typical cell, the small protruding metal cap is the positive terminal, and the flat metal disc is the negative terminal.

Takeaway. An electric cell provides energy and has two distinct terminals, positive and negative.

Battery: A Combination of Cells

More cells, more power.

A **battery** is a combination of two or more electric cells connected together. In a torch, cells are placed so that the **positive terminal of one cell connects to the negative terminal of the next**. This arrangement provides energy to the circuit for a longer time and/or provides more energy.

Takeaway. A battery is formed by connecting cells in a series, positive to negative.

Incandescent Lamp and Filament

The glowing wire inside.

An **incandescent lamp** has a thin wire called a **filament** fixed in the middle of a glass bulb. When electric current passes through the filament, it gets hot and glows to produce light. The filament is attached to two thicker wires that connect to the lamp's two terminals: the metal case and the metal tip at the b…

Takeaway. An incandescent lamp produces light when its filament gets hot due to electric current.

LED Lamp and Its Terminals

One-way street for current.

A **Light Emitting Diode (LED)** is a lamp that does not have a filament. It has two terminals: a **positive** terminal attached to a **longer wire** and a **negative** terminal attached to a **shorter wire**. An LED allows current to pass through it in **one direction only**.

Takeaway. An LED glows only when connected correctly, as it allows current to flow in one direction only.

Making an LED Glow

Connect positive to positive.

Takeaway. For an LED to glow, its positive terminal must connect to the battery's positive terminal and its negative terminal to the battery's negative terminal.

Electric Switch

Completes or breaks the path.

A **switch** is a simple device that either **completes** or **breaks** a circuit. In the **ON** position, the switch closes the gap in the circuit, allowing current to flow. In the **OFF** position, the switch creates an open gap, preventing current flow. A switch can be placed anywhere in a circuit.

Takeaway. A switch controls the flow of current by completing or breaking the circuit.

Circuit Diagrams and Symbols

Drawing circuits with symbols.

A **circuit diagram** is a representation of an electrical circuit using standard symbols. In the symbol for an electric cell, the **long line** represents the positive terminal, and the **short line** represents the negative terminal. Using symbols makes it easier to understand and draw circuits.

Takeaway. Circuit diagrams use standard symbols to represent electrical components clearly and simply.

Conductors and Insulators

Materials that pass or block current.

Materials through which electric current can flow easily are called **conductors** of electricity. Materials through which current cannot pass are called **insulators** or poor conductors. **Metals** are conductors, while **plastic, rubber, and ceramics** are insulators.

Takeaway. Conductors allow current to flow easily, while insulators do not allow current to pass through them.

Why Copper for Wires?

Best conductor, practical choice.

**Silver, copper, and gold** are the best electrical conductors. However, **copper** is mainly used for making electrical wires because of its comparatively **lower cost** and **abundant supply**. This makes it a practical choice for widespread use.

Takeaway. Copper is the most common material for wires because it is an excellent conductor, affordable, and plentiful.

Safety with Electricity

Electricity can be dangerous.

**Our body is a conductor of electricity.** Electric current passing through our body may cause severe injury or even death. Always handle electrical appliances with care. Never touch switches or plugs with wet hands, and never use electrical devices in wet areas.

Takeaway. Electricity is dangerous; always follow safety precautions and never experiment with mains power.

DC vs AC

Batteries vs wall sockets.

Electricity from batteries is called **Direct Current (DC)**, which powers small devices. Electricity from power plants that comes to wall sockets is called **Alternating Current (AC)**, which can run larger appliances.

Takeaway. Batteries provide Direct Current (DC), while wall sockets provide Alternating Current (AC).

Switch is Not a Source

Switch controls, doesn't create.

A common misconception is that a switch is the source of electric current. In reality, a **switch is not a source**; it is a device that helps to **complete or break** the circuit. The source of current is the electric cell or battery.

Takeaway. A switch is a control device, not a source of electric current.