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Chapter: 7th Science : Term 2 Unit 2 : Electricity

Student Activities

7th Science : Term 2 Unit 2 : Electricity : Student Activities with Questions Answers, Solution


Comb your dry hair. Immediately after combing the dry hair, bring the comb closer to the bits of paper .  what will you observe?

When you are getting up from the plastic chair , the nylon shirt seems to be stuck tothe chair and make crackling sound. What is the reason for the creation of the sound? A balloon sticks to wall without any adhesive after rubbing on your hand. Do you know the reason for all?

In all the above activities, when a body is rubbed against some other body become charged.

Conventional current is in the direction opposite to electron flow.

1 milliampere (mA) = 10-3 ampere.

                               = 1/1000 ampere

1 microampere (µA) = 10-6 ampere

                                 = 1/1000000 ampere


Shall we produce electricity at our home?

Materials required:

Zinc and copper electrodes, a light blub, connecting wires, and fruits such as lemons, orange,apples, grapes, and bananas.


1. Set up a circuit as shown in figure

2. Note the brightness of the blub when the circuit is connected to a lemon.

3. Repeat the experiment using the other fruits listed above. Do you notice the differences in the brightness of the bulb when it is connected to different fruits? Which fruit gives the greatest brightness? Why? (If you do not know please get the appropriate reason from your teacher)


In the above activity what makes enabled the bulb to glow. Why there is a difference in the brightness of the bulb? The reason is that the fruits  which you have connected to the bulb produces the electric energy at different levels

The sources which produce the small amount of electricity for shorter periods of time is called as electric cell or electro chemical cells. Electric cell converts chemical energy into electrical energy


I am so exhausted. I am going to faint. What first aid will you give me to wake up?

I'll recharge the secondary cell by connecting it to an electrical circuit. 

The dry cell is not really dry in nature but the quantity of water in it is very small, as the electrolyte is in thefrom of a paste. In other cells, the electrolyte is usually a solution


Make your own switch

Let us make a switch of our circuits. Take 10 cm long iron strip. Bend it twice as shown in figure. Now drive a nail into the bend of the wooden block. Nail one end of the strip to the other end of the wooden block so that its free end rests just above the first nail without touching it. Your switch is ready.

Would you like to test your switch? To do so, first set up the circuit as shown in the figure.

How would you use the switch to open or close the circuit.

If the bulb in your circuit glows when the metal strip of your switch is pressed on the nail and turns off when it is not, then your switch is working. The switch you made is a simple one. You may have seen many different types of switches on switchboards and appliances at your home and school. The switches are designed according to their usage, convenience and safety. But all of them work on the same principle. Switch is a mechanical component that consists of two or more terminals that are internally connected to a metal strip. Commonly used switches are listed below:

All muscles of our bodies move in response to electrical  impulses generated naturally in our bodies

Short circuit

You might have observed the spark in the electric pole located nearby your house. Do you know the cause of this electric spark? This is due to the short circuiting of electricity along its path. A short circuit is simply a low resistance connection between the two conductors supplying electrical power to any circuit. Arc welding is a common example of the practical application of the heating due to a short circuit.

This is the material used in SIM Cards, Computers, and ATM cards. Do you know by which material I am made up off?

 The chip  which are used in SIM Cards, Computers, and ATM cards are made up of semiconductors namely, silicon and germanium because of their electrical conductivity lies between a conductor and an insulator.

Wires made of copper, an nelectrical conductor, have very low resistance. Copper wires are used to carry current in households. These wires are in turn enclosed in electrical insulators, or materials of high electrical resistance. These materials are usually made of flexible plastic.


Materials required

* Iron nail

* Battery & Switch

* Wire

Take around 75 cm long piece of insulated flexible wire and an iron nail say about 8 - 10 cm long. Wind the wire tightly around the nail in the form of a coil. Connect the free ends of the wire to the terminals of a cell as shown. Place some pins on or near the end of the nail. Now switch on and switch off the current, What happens?

When the switch is kept in on position the pins starts to cling to the end of the nail.

When the electric current is switched off the coil generally loses its magnetism. Such coils are called as electromagnets.

The  polarities of both ends of the coil changes according to the direction of electric current passes.

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