CG Board Class 7 Science Electric Current and Its Effect

Electric Components and Symbols:

Electric components like cells, batteries, switches, and wires can be represented by symbols in circuit diagrams.
An electric cell has a positive terminal (represented by a longer line) and a negative terminal (represented by a thicker, shorter line).
Cells are connected in series to form batteries, which are used in various devices.
Switches have symbols to represent their ‘ON’ and ‘OFF’ positions.
Wires are represented by lines connecting components in circuit diagrams.

Conductors and Insulators:

Conductors allow electric current to pass through them and include metals, alloys, graphite, and electrolytes.
Insulators do not allow electric current to flow through them and include non-metals (except graphite), wood, glass, plastic, dry air, and most gases.
Conductors are used in electrical plugs, sockets, and switches, while insulators are used to cover electrical wires and prevent electric current from escaping.

Effects of Electric Current:

When an electric current passes through a conductor, it exhibits three main effects: heating, magnetic, and chemical.
The heating effect is due to the resistance offered by the conductor, which converts part of the electrical energy into heat. This principle is used in devices like electric bulbs, heaters, and soldering irons.

Safety Devices – Fuses:

Fuses are safety devices used to prevent electrical circuit damage and potential fires.
Fuses are made of materials like zinc or alloys of lead and tin with low melting points.
If the current in a circuit exceeds a safe limit, the fuse wire melts and breaks the circuit, preventing accidents.

Magnetic Effect of Electric Current:

When electric current flows through a wire, it generates a magnetic field.
Electromagnets are created by coiling a wire and are used in various applications, including electric bells, telephones, loudspeakers, cranes, and electric motors.

Electric Bell and Its Function:

An electric bell functions based on the magnetic effect of electric current.
It contains an electromagnet that attracts an iron armature when current flows through it, causing a hammer to strike a metallic cap, producing sound.
A push button is often used to activate electric bells, and they continue to ring as long as the button is pressed.

Electrical Safety Precautions:

Electrical accidents, such as electric shocks, can be dangerous, even fatal.
Precautions include securely screwing switches, plugs, and connections, covering exposed wires with insulating tape, using properly sized fuse wires, ensuring grounding in electrical devices, wearing protective gear during repairs, and cutting off the main switch in emergencies.
In case of an electric shock, use insulating materials like dry wood, rubber, or plastic to remove the person from the circuit to prevent further injuries.

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