Background

:

Everyone is familiar with the fact that when a pen made of plastic material is rubbed on the shirt sleeve, it will attract small pieces of paper. When dry hair is combed with a plastic comb, it may produce a crackling sound. The crackling sound is caused by small electric sparks which may be seen if the room is in darkness.

This phenomenon of electrical attraction leads to the introduction of static electricity or electrostatic. This simple hand-driven electrostatic generator will charge perspex, acetate or glass sheets for many electrostatic experiments.

Objectives

:

 The objective of this model is to indicate the presence of electrostatic charges. This model is made from easily available materials. Students can perform numerous experiments with static electricity.

Benefits for teaching and learning process

:

Students can understand :

1. The fundamental law of electrostatic.

2. Charges are electricity at high voltage. The phenomenon of lightning is     related to the high charges in the clouds.  

3. A conductor or a frame made of conducting material can shield off  electrostatic charges including lightning.

4. Electricity is a flow of electrons or negative charges.

Apparatus/ materials

:

1.  A piece of ½” thick plywood (12” x 12”).

2. Two pieces of wood (4” x 1” x 2”).

3. A piece of wood (12” x 1” x 2”).

4. Two pieces of ¾” P.V.C elbow joints.

5.  A piece of ¾” P.V.C tubing (12” long).

6. A piece of perspex (12” x 12”).

7. A piece of acetate or glass (12” x 12”).

8. Four pieces of ½” thick plywood (3” x 6”).

9. A piece of wool (3” x 6”), silk (3” x 6”), rubber sheet (3” x 6”) and polyethylene (3” x 6”).

10.  A milk bottle

11.  A metal can lid or disc, 3” in diameter.

12. A transparent plastic container or box (4” x 6” x 1”).

13. A fluorescent lamp and a neon bulb.

14.  A small piece of coloured paper, polystyrene and aluminium foil.

15. Six pieces of paper clips, small pieces of paper or pieces of polystyrene, 10 strips of tissue paper (1/4” x 8”)

16. A piece of wire mesh (12” x 12”), a thick piece of wire (14”) and a short piece of wire.

17. Straw and nylon, a plastic rod.

Construction and Implementation of the teaching aids

:

(a) THE ELECTROSTATIC GENERATOR

[Refer 1-D1, 1-D2 and 1-P1]

The plywood base, ½” x 12” x 12” and the wooden support for the rotating handle are assembled as shown. The rotating handle consisting of the ¾” P.V.C pipe and elbow joints are fitted through the 1” diameter hole in the wooden support. The friction pad is made up of 4 pieces of plywood, 3” x 6” x ½”. A piece of polyethylene (Refer C in 1-P1), wool (Refer D in 1-P1), silk (Refer E in 1-P1) and rubber sheet is glued to each friction pad. Fix the friction pad (Refer B in 1-P1) with the rubber base onto the rotating handle and place the perspex, 12” x 12” (Refer A in 1-P1), on the base of the electrostatic generator. Rotate the handle about 20 times. The perspex will be charged. Replace the perspex with acetate or glass and use the friction pad with silk. The charges produced on the perspex, acetate or glass is used for the following experiments.

(b)LIGHTING UP A FLUORESCENT LAMP

[Refer 1-D3,1-P2]

A short plastic rod is glued onto the centre of the metal can lid or disc, 3” in diameter. This metal lid is to transfer electrical charges from the perspex to the fluorescent lamp. Place the charge-carrying disc on the perspex. Touch the metal disc with the finger for a moment and then lift the disc by the handle. The disc is now positively charged. Hold the fluorescent lamp at one end and bring the charged disc to the other end. A spark will jump and the lamp will light up briefly.

(c) A PAPER LEAF ELECTROSCOPE

[Refer 1-D4 and 1-P3]

The paper leaves are cut from ordinary paper. The parts are assembled in a milk bottle as shown in the diagrams stated. Bring the charged perspex from the electrostatic generator close to the disc of the electroscope. The leaves will separate, showing that the electroscope has acquired a charge.

(d) ELECTROSTATIC “JUMPING PARTICLES”

[Refer 1-P4 and 1-P5]

Line the bottom of the transparent box with aluminium foil. Put some light materials such as tiny bits of cork, small pieces of paper or pieces of polystyrene into the box. Close the cover as shown. Rub over the cover of the box vigorously with wool and the particles will fly to the cover, staying there for a while and then flying off again and so forth.

(e) ELECTROSTATIC CHARGE DETECTOR

[Refer 1-D6 and 1-P6]

Insert pin through the centre of the lid so that its pointed end sticks upwards. Balance the stiff paper and its centre on the point of the pin so that it can easily rotate. Rub a straw with nylon near the charge detector and the stiff paper will turn and point in the direction of the straw.

(f) ELECTROSTATIC “TREE”

[Refer 1-D7and 1-P7]

Bend a thick piece of wire, 14” long, at each end and form two loops. Cut 10 strips of tissue paper, each ¼” wide and 8” long. Fix the strips of paper through one loop. Support the wire on a stand as shown. Charge the piece of perspex, 12” x 12”, with the electrostatic generator and bring it in contact with the free end of the thick wire. The strips of paper will spread out just like a palm tree.

(g) PITH BALLS  

[Refer 1-D8 and 1-P8]

Hang the two polystyrene balls as shown in the diagram, i.e. the pith balls which are very small, lightweight objects that pick up electric charge quite well. Bring a charged straw near and touch them. Remove the straw and the two polystyrene balls will repel each other.

(h) THE LEYDEN JAR

[Refer 1-D9 and 1-P9]

Wrap aluminium foil on the inside and outside of a glass as shown. Make a chain out of paper clips. Hang the chain on a plastic rod. The chain must touch the bottom of the inside foil. Bring the charged disc from the electrostatic generator near the top clip. A spark jumps to the clip. Repeat this a few times. Connect a short piece of wire from the outer foil to the clip. A powerful spark will be produced. The Leyden Jar can store electrical charges.

(i)  SHIELDING THE ELECTROSCOPE

[Refer 1-P10]

Place an electroscope inside a wire mesh frame as shown. Bring any charged material near and there will be no effect on the electroscope. The electrostatic charge cannot penetrate such a shield.

THE COMPLETE ELECTROSTATIC KIT

[Refer 1-P11]

Suggestion for modification

:

1. Measurements should be in S.I. units.

2. Be more specific in the instruction with clearer measurements and illustrations.

3. To include extension activities to clarify scientific concepts or principles, e.g. for objective No. (d).