Electricity is a powerful and versatile form of energy used in numerous devices. Understanding how electric current flows and the effects it produces is fundamental to using electricity safely and effectively.

When setting up an electric circuit, it can be complex to draw each component realistically. Using standard symbols simplifies drawing and representing circuits.

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Symbols Of Electric Components

To make drawing electric circuits easier and universally understandable, specific graphical **symbols** are used to represent common electric components. These symbols are standard, although slight variations might exist in different resources.

Table 14.1: Symbols for common electric circuit components:

S.No.	Electric component	Symbol
1.	Electric cell
2.	Electric bulb
3.	Switch in ‘ON’ position
4.	Switch in ‘OFF’ position
5.	Battery
6.	Wire

In the symbol for an electric cell, the **longer line** represents the **positive (+)** terminal, and the **shorter, thicker parallel line** represents the **negative (–)** terminal.

A **battery** is a combination of two or more electric cells connected together. To form a battery, cells are connected in series such that the **positive terminal of one cell is connected to the negative terminal of the next cell**. This arrangement provides a higher voltage (electrical push) than a single cell.

Devices like torches, remote controls, and toys use batteries, which can consist of multiple cells placed side-by-side or in sequence, with connections made by wires or metal strips between the positive terminal of one cell and the negative terminal of the next. Battery compartments usually indicate the correct orientation with '+' and '–' markings.

Cell holders are available to facilitate connecting multiple cells correctly to form batteries for experiments.

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Activity 14.1

Constructing a simple electric circuit with a cell, bulb, and switch demonstrates how components are physically connected. Drawing a **circuit diagram** of this physical setup using the standard symbols makes the circuit representation much simpler and clearer. A circuit diagram provides a blueprint of the electrical connections.

In a circuit diagram, the switch can be placed anywhere in the circuit path. When the switch is in the 'ON' position, the circuit forms a **complete loop** from the positive terminal of the battery/cell, through the components, and back to the negative terminal. This is a **closed circuit**, and electric current flows. When the switch is in the 'OFF' position, there is a **break** in the circuit, forming an **open circuit**, and no current flows through any part of the circuit.

An electric bulb glows when current flows through its filament, heating it to a high temperature. If the filament is broken (a fused bulb), the circuit within the bulb is incomplete, and the bulb cannot glow even if the external circuit is closed.

Heating Effect Of Electric Current

One of the notable effects of electric current is that when it flows through a wire or a component, it produces **heat**. This is known as the **heating effect of electric current**.

Safety Caution: Always use electric cells for the activities described here. Never experiment with electricity from mains supply, generators, or inverters, as it can cause dangerous electric shocks and burns. Lighted bulbs connected to the mains can be very hot and cause severe burns.

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Activity 14.2

Connecting a bulb to a cell and switch. When the switch is 'OFF', the bulb does not glow and is cool. When the switch is moved to 'ON' and the bulb glows for a minute, touching the bulb reveals that it has become warm or hot. After switching 'OFF' and letting it cool, it returns to its original temperature. This demonstrates that when electric current passes through the bulb's filament, it gets heated, causing the bulb to become warm.

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Activity 14.3

Constructing a circuit with a cell, switch, and a piece of **nichrome wire** tied between nails. Nichrome is a material commonly used in heating elements. When the switch is turned 'ON' for a few seconds, allowing current to flow through the nichrome wire, the wire becomes warm to the touch. This clearly shows that an electric current passing through a wire produces heat.

Many electric appliances utilize the heating effect of electric current. These appliances contain a coil of wire called an **element**. When current flows through the element, it becomes red hot and generates heat.

Examples of appliances using heating elements:

• Electric room heater
• Electric heater for cooking (hotplate)
• Immersion heater
• Electric iron
• Geyser (water heater)
• Electric kettle
• Hair dryer

The amount of heat produced in a wire depends on the **material** it is made of, its **length**, and its **thickness**. This allows wires to be designed to produce different amounts of heat for different applications.

While wires in normal circuits don't typically get very hot, the elements in heating appliances are designed to get hot enough to be visible (incandescent). The filament of an electric bulb is designed to get so hot that it emits light.

Incandescent bulbs, while providing light, also produce a lot of heat, wasting energy. More energy-efficient lighting sources like fluorescent tube-lights, Compact Fluorescent Lamps (CFLs), and especially Light Emitting Diode (LED) bulbs are preferred nowadays as they produce more light for the same amount of electricity consumed.

Electrical appliances should ideally be ISI marked, indicating conformity to safety and performance standards.

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Activity 14.4

Replacing the single cell with a battery of four cells (to increase the current) and replacing the nichrome wire with a thin strand of **steel wool** in the circuit. When the current is switched on, the thin steel wool strand, designed to melt at a relatively low temperature, quickly heats up, melts, and breaks due to the large current flowing through it. This demonstrates that if a sufficiently large current passes through a thin wire of certain materials, the wire can heat up enough to melt and break.

This property is the basis for **electric fuses**.

An **electric fuse** is a safety device designed to protect electrical circuits and appliances from damage due to excessive current, which can be caused by short circuits or overloads (connecting too many devices to one socket). A fuse contains a wire made of a special material that has a low melting point. If the current in the circuit exceeds a safe limit (for which the fuse is rated), the fuse wire heats up, melts, and breaks the circuit, interrupting the flow of current and preventing potential damage or fire.

Different types of fuses are used for different applications and current ratings. It is crucial to always use the correct type and rating of fuse for a circuit and to ensure it has an ISI mark for quality and safety. Never replace a fuse wire with just any ordinary wire or metal strip, as this defeats the safety purpose.

**Miniature Circuit Breakers (MCBs)** are modern alternatives to fuses. They are switches that automatically trip and break the circuit when the current exceeds a safe limit. Unlike fuses, they can be reset and turned back on after the fault is corrected.

Magnetic Effect Of Electric Current

Besides the heating effect, electric current also produces a **magnetic effect**. A wire carrying electric current behaves like a magnet.

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Activity 14.5

Setting up a circuit with a cell and switch, where a compass needle is placed inside a cardboard tray around which the connecting wire is wrapped a few times. When the switch is 'OFF', the compass needle points in its normal north-south direction. When the switch is turned 'ON', allowing current to flow through the wire, the compass needle **deflects** from its usual direction. This deflection indicates that the wire carrying current is affecting the magnetic needle, meaning the wire is behaving like a magnet. When the current is switched 'OFF', the needle returns to its original position.

This phenomenon was first observed by scientist **Hans Christian Oersted**. His discovery established that an electric current produces a magnetic field around the wire. This is known as the **magnetic effect of electric current**.

The magnetic effect allows electric current to be used to make magnets.

Electromagnet

The magnetic effect of electric current can be used to create temporary magnets called **electromagnets**.

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Activity 14.6

Winding an insulated wire tightly around an iron nail to form a coil. Connecting the ends of the wire to a cell through a switch. When the switch is 'ON', allowing current to flow through the coil, the iron nail acts like a magnet and can attract magnetic objects like pins. When the switch is 'OFF', the current stops, and the iron nail generally loses its magnetic properties, and the pins fall off.

A current-carrying coil of insulated wire wrapped around a piece of magnetic material (like iron) is called an **electromagnet**. Electromagnets are temporary magnets; their magnetism is present only when electric current flows through the coil. They can be made very strong by increasing the number of turns in the coil or increasing the current.

Electromagnets have numerous applications:

• Lifting heavy loads of magnetic material (like scrap iron) in cranes.
• Separating magnetic material from non-magnetic junk.
• Used by doctors to remove small magnetic foreign particles from the eye.
• Found in many toys and electrical devices.

Electric Bell

An **electric bell** is a common application that uses an electromagnet to produce sound.

The working principle of an electric bell (Fig. 14.20):

1. It contains a coil of wire wound around an iron piece, forming an **electromagnet**.
2. An iron strip with a hammer attached to one end is placed near the electromagnet.
3. A contact screw is positioned so that the iron strip touches it when in its resting position.
4. When the bell push is pressed, the circuit is completed. Current flows from the battery through the coil and the contact screw, reaching the iron strip and returning to the battery.
5. As current flows through the coil, it becomes an **electromagnet** and attracts the iron strip towards it.
6. As the iron strip moves towards the electromagnet, the hammer attached to it strikes a metal gong, producing a **sound**.
7. Simultaneously, the movement of the iron strip breaks the contact with the contact screw. This opens the circuit, and the current stops flowing through the coil.
8. Since the current stops, the coil loses its magnetism (electromagnetism). It no longer attracts the iron strip.
9. The iron strip springs back to its original position, touching the contact screw again. This closes the circuit once more, and current flows, making the electromagnet active again.
10. The process repeats rapidly: the electromagnet attracts the strip, the hammer strikes the gong, the circuit breaks, the magnet deactivates, the strip springs back, and the circuit is completed. This continuous cycle causes the hammer to strike the gong repeatedly, producing a sustained ringing sound.

The electric bell demonstrates how the magnetic effect of electric current and the properties of an electromagnet can be used to create mechanical movement and produce sound, all controlled by making and breaking an electric circuit.

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