Chapter 4 — Electricity: Magnetic and Heating Effects

When electric current flows through a conductor such as a wire, it produces a magnetic field around it. This phenomenon is known as the magnetic effect of electric current. The magnetic field disappears as soon as the current stops flowing.

Hans Christian Oersted (1777–1851), a professor at a university in Denmark, discovered in 1820 that electricity and magnetism are linked. He noticed that whenever an electrical circuit was closed or opened, the needle of a nearby magnetic compass deflected.

A current-carrying coil that behaves as a magnet is called an electromagnet. For practical applications, most electromagnets have an iron core to make them stronger. The coil acts as a magnet only when current flows; it loses its magnetic effect when the current is stopped.

The strength of an electromagnet can be increased by increasing the amount of electric current flowing through the coil, increasing the number of turns of the coil, or both. A battery with more cells gives a larger current and creates a stronger magnetic field.

When electric current passes through a conductor, the conductor faces resistance to the flow of current. This resistance causes some electrical energy to be converted into heat energy. The warming of a conductor due to the flow of electric current is known as the heating effect of electric current.

Many household appliances work on the heating effect of electric current, including electric room heaters, electric stoves, electric kettles, electric irons, water heating immersion rods, and hair dryers. All these devices contain a rod or coil of wire called a heating element.

Nichrome wire offers higher resistance compared to a copper wire of the same size and length. This higher resistance causes it to generate more heat for a given current, making it well-suited for use as a heating element in electrical appliances.

A Voltaic cell (also called a Galvanic cell) contains two metal rods called electrodes made of different materials and a liquid called an electrolyte (usually a weak acid or salt solution) placed in a container. A chemical reaction between the rods and the electrolyte produces electricity. When the chemicals are used up, the cell is 'dead' and cannot supply any more electricity.

In a Voltaic cell, the electrolyte is a liquid (a weak acid or salt solution). In a dry cell, the electrolyte is not a liquid but a thick moist paste, making dry cells more portable and convenient for everyday use. A dry cell has a zinc container as the negative terminal and a carbon rod covered with a metal cap as the positive terminal.

Rechargeable batteries can be recharged and reused multiple times, whereas dry cells are single-use — once the chemicals are used up, they must be disposed of. Rechargeable batteries are used in devices ranging from phones and laptops to inverters and electric vehicles. However, rechargeable batteries also wear out after being charged and used many times.

An electromagnet acts as a magnet only when electric current flows through its coil — it loses its magnetic effect when the current is stopped. A permanent magnet retains its magnetism without any current. The poles of an electromagnet can also be reversed by changing the direction of the current, which is not possible with a permanent magnet.

Yes. Lemon juice acts as an electrolyte, while copper wire and an iron nail act as the two different metal electrodes. When connected in series with other lemon cells, enough current is produced to light up an LED. Salt solutions can also be used as the electrolyte instead of lemon juice.

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