A cell is the most basic component in an electric circuit. The fundamental action of the cell is to convert chemical energy into electric energy. Furthermore, when two terminals are connected to a cell, an electric current passes through them. In an electric circuit, a series of cells are connected which is called a battery. Batteries are used in all types of applications including toys, TV remotes, smartphones and more.

An electric circuit is defined by a closed connection of batteries or cells, resistors, transistors, capacitors or other electrical components through which electrical current flows.

For the simplicity of drawing an electric circuit diagram, different electrical components are drawn in symbols. These are called symbols of the electrical circuit.

A circuit diagram is a pictorial representation of how electric components are connected. It also depicts the current flow in the circuit. A circuit diagram helps explain an electric circuit easily and hence identifies errors faster.

Consider the example of a bulb. When a bulb is kept switched on for some time, it begins to emit heat. This effect is known as the Heating effect of Electric current. Some of the characteristics of the effect are -

• The heating effect of electric current is dependent on the thickness, length, and material of the wire.
• A wire connected to the circuit becomes heated when an electric current travels across it. This is the simplest way to see how electric current heats things. The effect is used in several daily appliances such as the electric heater, microwave oven and more. 
• They are also used in safety devices like fuses.

A fuse is an ideal example of the heating effect of electric current. A fuse is a safety component installed in an electric circuit. It is made up of wires which melt  when a huge load of current passes through it. Therefore, it prevents any problems related to circuit damage or fire.

The magnetic effect of electric current was discovered by Hans Christian Oersted. It states that when a current is flowing through a wire and a compass is brought close to it, the needle will move. The greater the intensity of  the current, the more the deflection; conversely, the lesser the intensity, the smaller the deflection. Simultaneously, reversing the current in the wire causes the magnetic needle to move in the opposite direction.

• When electricity flows through a wire, it acts like a magnet and creates a magnetic field around it. This is the most simple approach to learning the magnetic effect of electric current.
• This effect is used in different applications such as loudspeakers, motors, electrical fans and others.

An electromagnet is the perfect application of the magnetic effect of electric current. An electromagnet is a man-made magnet that generates a magnetic field around a conductor when an electric current passes through it. When there is no current flowing through the conductor, the magnetic field ceases to exist.

The electromagnet has a wide range of applications including MRI machines used by doctors, relays, transformers and others.

 

• Electromagnets are used to make an electric bell.
• An electromagnet is made up of a coil of wires in an electric bell.
• The hammer is connected to the electromagnet via the iron strip.
• A contact screw is close to the iron strip. 
• The circuit is complete when the contact screw makes contact with the iron strip, and the electromagnet activates.
• The magnet attracts the iron strip, which causes the hammer to strike the gong, resulting in a sound. The contact screw disconnects from the iron strip as soon as the gong is struck, breaking the circuit. The electromagnet's magnetism is lost.
• The iron strip comes into contact with the contact screw once more, completing the circuit. In addition, the wire coil functions as an electromagnet. The bell tolls once more. This technique is repeated fewer times till the switch is turned on.
• An electric bell operates on this principle.

1. Name two effects of Electric Current 

There are two main effects of Electric Current.

• Heating effect of Electric Current - It states that when an electric current passes through a conductor it generates heat after some time. Some of its applications are electric heater, oven, etc.
• Magnetic effect of Electric Current - This effect states that when an electric current passes through a conductor, it generates a magnetic field around it. Some of the examples include electric motors, transformers, loudspeakers etc.

2. Explain why a compass needle stored nearby is diverted from its north-south position when the current is switched on through a wire?

When the current passes through a wire, a magnetic field is generated around it. Due to this, the compass needle is affected by the magnetic field and gets deflected from the north-south position.

3. What is an electric circuit?

An electric circuit is a closed connection of different electrical components such as resistors, transistors, capacitors and more which is powered by a battery. 

4. Do you believe you could use an electromagnet to separate plastic bags from a waste heap? Explain.

A plastic bag does not have any magnetic properties hence an electromagnet cannot be used to separate plastic bags from the waste heap.

5. In your home, an electrician is working on some repairs. He wants to use a piece of wire to replace a fuse. Give reasons whether you agree or disagree.

A piece of wire has a high melting point compared to a fuse. When a huge load of current passes through the fuse, it melts, shutting the circuit off. In case the melting point of the wire is high, it will not melt during a high current load and can cause power overload or fire.

6. Is the circuit complete if the filament of the bulb breaks? Is the light bulb still on?

The filament of the bulb is part of the electric circuit. If it is broken then the circuit does not have a closed connection, hence the light bulb will not glow.

State True or False from the following statements.

(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. - False

(b) An electric bell has an electromagnet. - True

(c) An electromagnet does not attract a piece of iron. - False

(d) When the electric current runs through the fuse and exceeds a certain limit, the fuse wire melts and breaks. - True

Fill in the blanks:

(a) A longer line in the symbol for a cell represents its positive terminal.

(b) The safety device based on the heating effect of electric current is called a fuse 

(c) When a current is switched ‘on’ in a room heater, it produces heat

(d) The combination of two or more cells is called a battery.

One of the most important concepts in Class 7 science is the electric current and its effects. The principles of Electric Current and Its Effects are required for practically designing electrical circuits. Furthermore, the effects induced by an electric current, such as the magnetic effect and the heating effect, are important concepts that we use in our daily lives. 

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