Electric circuits, conductors and insulators — lesson. Physics CBSE Live product, Class 7 (2025-26).

Electric devices work only when electric current flows through a complete circuit. By performing simple activities using electric cells, bulbs, LEDs, and connecting wires, we can understand how an electric circuit is formed and how current flows through it. They also explain why an incandescent lamp may fuse and why LEDs glow only in one direction.

Electrical circuit:

An electric lamp glows when one terminal of the lamp is connected to one terminal of the electric cell, and the other terminal of the lamp is connected to the other terminal of the cell. This arrangement forms an electrical circuit.

Flow of electric current:

An electrical circuit provides a complete path through which electric current can flow. The lamp glows only when electric current passes through the circuit.

Direction of electric current:

By convention, the direction of electric current in a circuit is taken from the positive terminal to the negative terminal of the electric cell.

Direction of electric current

Glowing of an incandescent lamp:

When the terminals of the lamp are connected to the terminals of the electric cell using wires, electric current flows through the filament of the incandescent lamp, causing it to glow. In an incandescent lamp, it does not matter which terminal is connected to the positive or negative terminal of the cell. The lamp will glow as long as the circuit is complete and current flows through the filament.

Fused lamp and broken filament:

Sometimes, an incandescent lamp does not glow even when it is properly connected to a cell. In such cases, we say that the lamp has fused, which usually happens due to a broken filament. A broken filament interrupts the flow of electric current, preventing the lamp from glowing.

Connecting cells placed side by side:

Sometimes, you may find a device where the cells are placed side by side. In such cases, the terminals of the cells are connected using a thick wire or metal strip that joins the positive terminal of one cell to the negative terminal of the next. To ensure correct placement, (\(+\)) and (\(-\)) symbols are usually printed inside the battery compartment.

Conductors:

Materials through which electric current can pass easily are called conductors or good conductors of electricity.

Example:

Copper, graphite, silver, gold, aluminium, steel, etc.

Copper, graphite and steel

Insulators:

Materials through which electric current cannot pass are called insulators or poor conductors of electricity.

Example:

Wood, plastic, rubber, glass, paper, etc.

Wood, rubber, paper and plastic

Electrical conductors used for making wires:

Silver, copper, and gold are among the best conductors of electricity. However, copper is most commonly used for making electrical wires because it is less expensive and easily available compared to silver and gold. Different types of electrical wires are used for different purposes depending on their application.

Why are electrical wires covered with insulators?

Materials such as plastic, rubber, and ceramics do not allow electric current to pass through them. These materials are electrical insulators. Covering electrical wires with insulators prevents the electric current from coming into direct contact with our body, ensuring safety.

Electrical wires with insulation

Uses of conductors and insulators:

Both conductors and insulators play an important role in electrical systems. Conductors are used to make electrical wires, switches, plug connectors, and sockets because they allow electric current to flow easily. Insulators like rubber, plastic, and ceramics are used to cover wires, plug tops, and switches to protect users from electric shock.

Plug tops

Caution: Electrical safety

The human body is a conductor of electricity. If electric current passes through our body, it can cause serious injury or even death. Therefore, always handle electrical appliances carefully. Never touch switches or plugs with wet hands, avoid using electrical devices in wet places, and do not use appliances with damaged wires or broken plugs.

Types of electric current: DC and AC

Have you ever thought about how electricity from a cell or battery differs from the electricity supplied through a wall socket? Electricity from cells and batteries is mainly used to operate small devices and is called Direct Current (DC). On the other hand, electricity supplied to wall sockets comes from power stations, is called Alternating Current (AC), and is used to run larger electrical appliances.

2. Electric circuits, conductors and insulators

Theory: