The study of Physics Topics has helped humanity develop technologies like electricity, computers, and space travel.
What is Electricity and Uses of Electric Cell
Electricity is a very clean form of energy. Electricity is useful because it can be converted easily into various other forms of energy such as heat energy, light energy, mechanical energy, sound energy and magnetism, etc. We use electricity to run many appliances (or machines) in our day to day life which make our work easier.
For example, at the touch of a switch, we can make an electric bulb (or tube- light) glow and produce light. Thus, electricity is used for lighting purposes. Electricity makes it possible to light up our homes, offices, markets, roads and factories after sunset when it gets dark. This helps us to continue working even at night.
Electricity is also used to run fans, coolers and air conditioners which make our life cool and comfor¬table during hot summer days. The refrigerator (fridge) in our homes also works with electricity. Electricity water pumps in our homes which lift water from the ground level to the roof-top tank.
In rural areas (village areas), electricity is used to pump underground water from tube-wells for irrigation in fields. A large number of other appliances in our homes such as electric iron, mixer and grinder, microwave oven, electric geyser, electric kettle, washing machine, radio set, television set, stereo system and computer, etc., all work because there is electricity.
A large number of machines in shops and factories run on electricity. Even the electric trains run with electricity. We use electricity everyday. We cannot see electricity but we can observe what it can do. For example, we can observe that electricity can light up a bulb or rotate a ceiling fan.
Where does the electricity in homes come from ? Electricity is produced at power stations (also known as power plants). The big electric generators at power stations produce electricity. From the power station, electricity is brought to our homes through thick wires fixed atop tall electric poles.
Underground electric wires (called cables) are also used to bring electricity into our homes. Though electricity is very useful but it can also be very dangerous. If electric wires and electrical appliances are handled carelessly, then a person can get electric shock which may cause severe burns and even death (see Figure).
Improper handling of electricity can also cause fires. A danger sign (consisting of a skull and bones) is usually dis-played on electric poles, electric substations, electric transformers and many other places to warn the people that they should not come in contact with them because electricity can be very dangerous (see Figure).
It should be noted that the electricity produced by portable electric generators (used in homes and shops during power cuts) is equally dangerous. We should never use electricity from power points (sockets) in our homes or school for performing science experiments because it is very unsafe and dangerous to do so.
We will now describe a safe source of electricity which we can use for our study of electricity by performing experiments. We can use an electric cell to get electricity that is safe for performing experiments. Please note that an electric cell is commonly known as ‘dry cell’ or just ‘cell’.
A cell provides much less electricity than that provided by power stations. For example, a single electric cell usually provides only 1.5 volt of electricity whereas the electricity from power stations which is used in our homes is at 220 volts ! If two (or more) cells are joined together, they make a battery. We should use only electric cells (or battery made of electric cells) for performing all the experiments or activities based on electricity (or electric current) (see Figure).
Cells and batteries are available in the market in different shapes and sizes depending on their use. The wristwatches, electric clocks, calculators, toys, mobile phones, cameras, torches, and TV remotes use electricity from various types of cells and batteries for their working. In order to get electricity (or electric current) from a cell or battery, we have to connect it into a circuit. We will discuss this in detail after a while.
Electric Cell (Dry Cell or just Cell)
An electric cell is a device which produces a small amount of electricity. Thus, electric cell is a source of electricity. In fact, electric cell is a source of safe electricity as well as portable electricity. The electric cell which we use in torch, etc., is commonly known as ‘dry cell’ or just ‘cell’. It is called dry cell because it does not contain any liquid chemical. A common electric cell is shown in Figure.
The electric cell is a cylindrical device having a small metal cap on one side and a metal disc on the other side (see Figure). The electric cell has two terminals : a positive terminal and a negative terminal. The metal cap is positive terminal of the electric cell whereas metal disc is the negative terminal of the electric cell.
The positive terminal of electric cell is marked ‘plus’ (+) whereas the negative terminal of the electric cell is marked ‘minus’ (-). We can also say that an electric cell has two ends : a positive end marked +, and a negative end marked – .
An electric cell has a number of chemicals stored in it. The electric cell produces electricity from the chemicals stored inside it. When all the chemicals in the electric cell are used up, the electric cell stops producing electricity. This electric cell has then to be thrown away and replaced with a cells cannot be recharged.
The electric cells or batteries used in cars, cameras and mobile phones, etc., can, however, be recharged again and again for many years. Electric cells are used as a source of electricity in torches, wristwatches, alarm clocks, transistor radios, TV remotes, cameras, mobile phones, toys and many other devices. The shape, size and type of cells used for various purposes may, however, be different.
We also use electric cells as a source of electricity for performing science experiments in the school laboratory. In our experiments, we should always join the two terminals of a cell by connecting them through wires containing a device such as a torch bulb and a switch, etc. We should never join the two terminals (+ and -) of a cell directly by a wire.
This is because if we join the two terminals of a cell directly by a wire only, then the chemicals present in the cell get used up very fast, the cell gets damaged quickly and hence stops working. Before we describe how an electric cell is used to light up a torch bulb, we should know the construction and working of the torch bulb. This is discussed below.
The small electric bulb which produces light when a torch is switched on is called a ‘torch bulb’. The torch bulb consists of a small glass bulb fixed on a metal case [see Figure (a)]. Inside the glass bulb, there is a very ‘thin wire’ fixed between two thick wires.
The thin wire inside the bulb is called filament of the bulb. Filament is usually made of a very thin tungsten wire. It is the filament of the bulb which glows when electricity from a cell is passed through it. The two thick wires inside the glass bulb provide support to the filament and also make the connection of the filament to the outer circuit.
The lower end of one of the thick wires is connected to the metal tip at the bottom of the bulb whereas the lower end of the other thick wire is connected to the metal case of the bulb [see Figure (b)]. The ‘metal tip’ at the base of the bulb and the ‘metal case’ of the bulb are the two terminals of the torch bulb. So, a torch bulb has two terminals.
The two terminals of a torch bulb do not touch each other, they are separated by an insulating material between them. Please note that the metal case of the torch bulb is shaped like a screw so that it can be fixed in the bulb holder (like that in a torch, etc.).
We have already studied that an electric cell has two terminals (which are marked + and – ). And now we see that a torch bulb has also two terminals (though they are not marked + and -). When the two terminals of a cell are connected to the two terminals of a torch bulb by using wires, the electric current passes through the filament of the bulb and it starts glowing (gives off light).
In other words, the torch bulb lights up when its metal tip and metal case are connected to a cell through wires. Actually, when electricity (or electric current) from the cell passes through the filament of the bulb, the filament gets heated too much. The filament becomes white hot and starts giving light. So, it is the heating effect produced by electricity from the cell which makes a torch bulb work and produce light. Thus, a torch bulb converts electricity into light.
The electric bulbs used in our homes also have a design similar to that of a torch bulb but they are much bigger. So, in general we can say that an electric bulb has a filament which is connected to two terminals. The electric bulb glows when electric current passes through its filament. Please note that the small amount of electricity produced by one or two dry cells can light up only a small electric bulb like a torch bulb, it cannot light up the big electric bulb which we use for lighting in our homes.
We will now describe an electric circuit. Before we do that, we should keep in mind that electric wires have a plastic insulation (plastic covering) over them. So, in order to use electric wires in electric circuits, some of the insulation from both ends of each piece of wire has to be removed to get bare wires for making connections.
Another point to be noted is that the bare ends of electric wires can be connected to the two terminals of a cell by using rubber bands or adhesive tape used by electricians. The electric wires can be connected to the two terminals of a torch bulb by using adhesive tape (or a bulb holder).