Science‎ > ‎


posted Sep 26, 2017, 3:48 PM by Upali Salpadoru   [ updated Oct 9, 2017, 12:24 AM ]

Electroscope is a very simple instrument made to detect electric charges. One way to produce an electric charge is to rub two insulating materials together.
Click : Static electricity for more.

 Fig.1. Charging a comb.   Fig.2. A negatively charged comb attracting uncharged paper.

Picture shows how a plastic comb can be charged. The senses we have are not sufficient to observe the charge directly, but the comb, if charged will be able to pick up tiny pieces of paper.
An electroscope is a simple instrument we can even make to study electric charges.
Requirements: 1. A thin metal sheet that can be easily cut. (4 cm. x10 cm. G.I., Al or Cu),  2. Plastic or glass bottle with a cork, 3. A paper clip,  4. A very small piece of aluminium foil.(2.5cmx1cm)
Tools:  A pair of scissors or a metal cutting sheers.

Step 1.
Cut the metal strip according to the shape shown . (It is not necessary to adhere to the measurements given. They may be varied according to the size of the bottle.)
Step 2.
Bend the circular part to form a horizontal plate.    
Step 3.
Attach the aluminium foil strip to the lower end tightly using a paper clip. Contact must be firm.

Experiments with the electroscope.
1. Use different insulating  materials to rub with each other such as plastic and fur, Glass and silk, wool and pencil etc.,  Then bring the items, one by one close to the plate of your electroscope. Record what happens to the ends of the foil.

2. Select a substance or an item that give a high deflection . Charge this and make contact with the plate of the electroscope. Do this several times until the foil remain divulged.
Then as in the ex.1. Bring various items near the plate.
Complete a table similar to this to record the results.

Item used to charge the electroscope,


Two substances rubbed.

What happened to foils.



No change.

Low repulsion

.High repulsion


Comb (plastic)
















  For a better understanding click Static electricity and Photo electricity.

Part A Multiple Choice Questions.

  1. Smallest and lightest particle in an atom.

A- Electron    B- Proton   C- Ion      D- Neutron.

2.  A particle that will not have a negative charge.

A- Atom    B - Proton  C - Ion   D- .Molecule

3. According to convention, the current flows from

A- Low charge to high charge  B - Negative charge to positive charge

C- Positive charge to negative charge D- Conductors to insulators.

4.  Electrostatic attraction can never be between

A-  Positive charge and a negative charge.

B-  Positive charge and neutral body.

C-  Negative charge and a neutral body.

D - Similar charges.

5. The best way to induce a positive charge in an electroscope will be

A - To rub it with silk  B- To rub it with fur

C - Bring a positively charged body near,  earth the electroscope and remove the charged body.

D- Bring a negatively charged body near, earth the electroscope and remove the charged body.

6-  What kind of substances can easily be electrically charged by rubbing.

   A= Metals   B - Good conductors  C= Semiconductors D- Insulators.

7. Carriers of electric charges in a circuit can only be

A- electrons and ions  B- Electrons and Protons  C-  electrons and negative ions

D- electrons .

8. Which of these actions can produce  an ‘ion’.

1- Removal of one or more electrons from an atom.

2- Removal of one or more electrons from a molecule.

3- Adding of electrons to an atom.

4- Adding of electrons to a molecule.

A- All are correct.   B- Only 1 is correct.C- Only 1 and 2 are correct

D- Only 3  and 4 are correct.

5 x8 = 40

Part B


1.1 Name the charge in the comb.

1.2 What does the red arrow indicate?

1.3 Why do the aluminium foils move apart?

1.4 What would happen when the comb contacts the coil ?

1.5 Comb is taken away after contact. What would happen to foils?

10 marks


  a)   Mention how the foil will behave in each case.

  b)   Explain the reason.



                   A                         B                   C                    

2.1 In A a positively charged glass rod is held near.

2.2 In B The charged glass touches the electroscope.

2.3 In C  A charged comb is brought near immediately after.

2.4  In D electroscope is connected to earth.
2.5  In E and F earth connection is broken and the comb removed.

                                                                                                                                         4x5 =20


Two balloons Red and Blue, were given opposite electrical charges. Briefly explain how you may select the negative and the positive one. You are supplied with a glass rod. a piece of silk, and some thread.

5 marks.


This is a device that can store electric charges. When a charge is applied to the small sphere A. The charges go down as shown by the arrow and accumulates in the grey cup D. The foil E , wrapped outside develops an induced charge.

Answer the following:-

  1. Are these conductors or insulators?  A-              B-            C-     

                                                         D                 E.

                 2. What subatomic particles will be going down the arrow when charging the Leyden jar?

                 3. What will be the charge on E.?

4.Explain how to obtain a spark after the jar is charged.

5.What may happen if E is connected to Earth?