Short Paragraph on Electricity and its Uses

Electricity and its Uses

Electricity is produced from coal, water, or air. Electrical energy is perhaps the most useful form of energy. In our daily life, we can see a large number of appliances operated by electricity. We are familiar with air currents and water currents. We know that flowing water constitutes water current in rivers. Similarly, if the electric charge flows through a conductor (for example, through a metallic wire), we say that there is an electric current in the conductor. In a torch, we know that the cells (or a battery, when placed in proper order) provide a flow of charges or an electric current through the torch bulb to glow. We have also seen that the torch gives light only when its switch is on. What does a switch do?

A switch makes a conducting link between the cell and the bulb. A continuous and closed path of an electric current is called an electric circuit. Now, if the circuit is broken anywhere (or the switch of the torch is turned off), the current stops flowing and the bulb does not glow. How do we express electric current? Electric current is expressed by the amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges. In circuits using metallic wires, electrons constitute the flow of charges.

However, electrons were not known at the time when the phenomenon of electricity was first observed. So, electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the direction of electric current. Conventionally, in an electric circuit, the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges.

‘Flow’ of charges inside a wire

How does a metal conduct electricity? You would think that a low-energy electron would have great difficulty passing through a solid conductor. Inside the solid, the atoms are packed together with very little spacing between them. But it turns out that the electrons are able to ‘travel’ through a perfect solid crystal smoothly and easily, almost as if they were in a vacuum. The ‘motion’ of electrons in a conductor, however, is very different from that of charges in empty space. When a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’. One can calculate this drift speed of electrons for a typical copper wire carrying a small current, and it is found to be actually very small, of the order of 1 mm s-1. 

How is it then that an electric bulb lights up as soon as we turn the switch on? It cannot be that a current starts only when an electron from one terminal of the electric supply physically reaches the other terminal through the bulb, because the physical drift of electrons in the conducting wires is a very slow process. The exact mechanism of the current flow, which takes place with a speed close to the speed of light, is fascinating, but it is beyond the scope of this book. Do you feel like probing this question at an advanced level?


The following are the uses of Electricity:

1. Electrical energy is used to produce heat, as in a heater or an electric kettle or in an immersion heater. It is used to produce light, as in a bulb or a tube light.

2. It is used to produce sound, as in a call bell or blowing a horn in a motorcar or operating the siren in a mill or a factory.

3. It is used for operating pump sets in a bore well, fodder-cutting machines, and cold storages for storing fruits and vegetables.

4. Electrical energy can also produce motion. When you switch on a fan, it starts moving.

5. Electrical energy is also used for moving conveyor belts that carry materials from one place to another.

6. Radio, television, tape recorders, refrigerators, and computers are operated by electricity.

1. On what factors does the resistance of a conductor depend?
The resistance of a conductor depends on the cross-sectional area of the conductor, the length of the conductor, and its resistivity. It is important to note that electrical conductivity and resistivity are inversely proportional, meaning that the more conductive something is the less resistive it is.

2. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
The current will flow more easily through a thick wire than through a thin wire of the same material when connected to the same source. This is due to the fact that the resistance of a wire is inversely proportional to the square of its diameter.

3. Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Solution: When the potential difference across the two ends of the electrical component becomes half its former value, the current through it also becomes half. Since `I = V//R`, when pd becomes `I//2` the resistance (R ) of the component remains constant.

4. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
An electric toaster and iron coils are made of an alloy rather than a pure metal because an alloy has a higher resistance than a pure metal. The alloys also do not melt easily at high temperatures.

5. A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit.
We are given, I = 0.5 A; t = 10 min = 600 s.
From Eq. (12.1), we have
Q = It
    = 0.5 A × 600 s
    = 300 C
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