We need energy to do our daily activities. In the past people used human labour to do many work. Today we use different types of energy sources to make our work easier. Electricity is one such type.

There are so many other day-to-day activities where electricity is used.

Electricity is used in some vehicles to operate machines in factories, operate air conditioners and communication purposes etc.

Uses of electricity are unlimited.

Simple ways of generating electricity

Electricity is very useful to human beings. Let’s find out the ways of generating electricity. People use different methods to generate electricity in different instances. Now let’s do the following activity to find out ways of generating electricity.

Dynamo, solar cells and dry cells are commonly used methods of generating electricity.

Let's find more about methods of generating eletricity.

You can do the above activity easily even at home. You will understand that electricity can be generated easily from it. Electricity is generated in electric cells through a similar process as above.

You may have understood that an electric current was generated by moving magnet inside the coil of wire in the above activity. In bicycle dynamo, generators, hydropower stations, wind power stations, electricity is generated in the same manner as above.

Let’s do another activity to generate electricity.

We obtain electricity from hydropower stations. Let’s simply demonstrate the process that takes place in a hydropower station.

In this activity the motor operates as a simple dynamo.

The simple activity we did above is used in power stations to generate electricity at a large scale. Following are some methods used to generate electricity at a large scale.

Power Stations

Table 8.1.shows different types of power stations and methods they use to generate electricity in Sri Lanka.

Some countries in the world use nuclear power, solar power and sea waves to generate electricity.

Electric cells

The above set up demonstrates a simple cell. Here, the bulb lights up. But after sometime the brightness of the bulb decreases.

To overcome the weaknesses of the simple cell various types of cells were invented.

1. Chemical Cells

a. Primary cells

Chemical in these cells are exhausted in use and after a certain period of time, they become inactive.

This type of cells cannot be recharged. The simple cell used in activity 8.4 belongs to this type.

Eg:- dry cells, wrist watch batteries, certain camera batteries

b. Secondary cells

Chemical of these cells too get exhausted and become inactive after a certain period of time. They can be recharged by supplying electricity to them. So, we can use them for a longer period.

Eg:- car batteries (lead acid accumulator), mobile phone batteries, certain torch batteries

2. Solar cells

Let's connect an electric appliance to an electric cell with conductive wires.

When we switch on the circuit, an electric current flows through conductive wires that lights up the torch bulb.

A system which allows to flow an electric current through it, is known as an electric circuit.

How long did you take to draw the sketch in activity 8.5 ?

Find out an easy way to draw this circuit by discussing with your friends.

The accessories you used to prepare the circuit are known as electrical

appliances. Apart from them, there are various other appliances used in

different types of circuits.

Fig. 8.18 shows some different types of electric appliances used in

electric circuits.

Using symbols for electric appliances in circuits

Let’s pay our attention to activity 8.5 again.You must have taken a lot of time to draw this circuit in your book. To overcome this problem, we can use standard symbols for electric appliances.

Table 8.2 shows some of the common standard symbols used to draw electric circuits.

You can divide the materials in activity 8.8 into two categories.

•  Materials which carry electricity

•  Materials which do not carry electricity

•  Materials that conduct electricity, are known as conductors.

•  Materials that do not conduct electricity, are known as insulators.

Aluminium, silver and copper are some examples for good conductors. Ceramic, mica, ebonite, glass, plastic and rubber are some good insulators.

The accessories used in electronic circuits are called electronic

appliances.

Now let's learn about some electronic appliances that are used in day to

day life.

01. Diode

Let's do the following activity to learn about diodes.

You will observe that the bulb lights up only when the diode is kept in

a specific way. Accordingly, we can say that the current flows through

a diode only in a particular direction.

There are various types of diodes available in the market.

Rectifying diodes are the most commonly used type. Given below is

the outer appearance of a rectifying diode.

The main function of a diode is to let the current flow in one direction only.

2. Light emitting diode

You may have seen a small bulb lighting up in radios, televisions etc, when they are switched on. They are not really bulbs. They are called light emitting diodes(LED).

3. Resistors

There is a loss of current when lengthy electric wires are used in circuits . That is because of the barrier to the flow of current in the conductor.

Let's do the activity 8.13 to observe how this can happen in a conductor.

The barrier to the flow of current is named as electric resistance. The unit used to measure resistance is Ohm (Ω).

You can buy resistors of different values from the market.

4. Light Depending Resistors (LDR)

By doing the following activity, you can understand the function of an LDR.

When light falls on LDR, a high current flows through the circuit. By shading the light, the flow of current through the circuit reduces gradually. Can you suggest the reason for this?

When the light falls on the LDR the resistance of it reduces, and when there is less light falling on the LDR the resistance increases.

Therefore, light depending resistors (LDR) are resistors, that change based on the amount of light falling on it.

The consumption of electricity is increasing day by day. At present, the generated electricity is not sufficient. Therefore, there is an energy crisis in the world.

Conservation of electricity

It's time to use electricity economically. Here are some ways of

conserving electricity.

1. Use efficient bulbs.

The amount of current used in CFL and LED bulbs is even less than

1/5th of the current used in normal bulbs. Also, their life span is ten

times more than a normal bulb.

2. Switch off the appliances when they are not in use. Keeping televisions, Computers, telephone chargers in by stand mode is a waste of electricity.

3. Do not increase the sound of televisions and radios unnecessarily.

4. At present, there are televisions and computers with LCD and LED screens. They minimize the consumption of electricity.

5. At present, there are refrigerators which minimize the consumption

of electricity.

We can save electricity according to the way we use the refrigerator

at home.

•  Minimize the number of times you open the door of the refrigerator.

•  Cool the warm food items before putting them into the refrigerator.

•  Place the refrigerator in a place without light.

•  Keep a space between the wall and the refrigerator.

•  Avoid putting unnecessary things in the refrigerator.

6. By ironing many clothes at once than ironing one at a time, we can minimize the wastage of electricity.

Prevention of accidents cause by electricity

Electricity is sometimes a good servant but sometimes a bad lord too. Careless use of electricity may cause damages to the property, serious accidents and sometimes even death.

Apart from the above facts, we must pay attention to these facts as well.

• Keep electric wires and extension cords out of reach of childern.

• Do not let children to go near electric sockets.

• Unplug multi sockets when not in use.

• Do not let childern to use electric appliances without the inspection of an adult.

• Do not touch electric circuits & appliances with wet hand.

• When using electric irons or other appliances, wear rubber slippers or stand on a rubber door-mat.

• If you notice some unusual nature of an electric appliance or a circuit, call your electrcity service provider immediately.

• Disconnect the main switch in your house during flood.

• It is compulsory to fix a trip switch to the domestic electric circuit.

• The damages caused by accidents related to electricity can be prevented by the automatic function of this switch.

Exercise