CBSE Book Class 8 Science Activity Mysterious Forces

SOME NATURAL PHENOMENA

There was a power cut. It was pitch dark in Soma's room. Soma was changing her woolen sweater, when she suddenly saw sparks flying from her sweater. What was that? She was too scared. Do you know that it is due to static electric charges developed on wool fibres due to rubbing with other cloth? 

Let us perform some activities to discover more about these static electric charges.

1. Can you fill up an old nylon stocking with absolutely nothing in it? Hold the toe of the stocking against the wall with one hand. With the other hand rub the stocking about 10 times with a dry, polythene bag or cellophone paper. Remove the stocking from the wall and let it hang freely. You will be amazed to see how it blows up as though filled with an invisible leg. It will also cling to the wall or to your body. On one hand, it is attracted to objects nearby, and on the other hand it seems to repel itself. Why does this happen? 

2. Put  small,  light  objects  like  puffed  rice/rice  flakes/sawdust/tiny  bits  of  paper  into  a  shallow transparent plastic or glass container. Cover it with rubber baloon sheet. Rub the cover with nylon, wool or fur. Some of the material will jump up and stick to the cover. Others jump up and down.

3. Charge a balloon by rubbing it with wool. Bring this charged balloon over the hair on your head. Watch your hair stand on its end!

4. Bring a charged plastic comb near some salt on a piece of paper. Watch the salt jump and hit the comb. Some of the bits of salt jump off almost immediately and cause faint sounds like the pitterpatter of raindrops. Other bits of salt stick to the comb.

5. Use these static electric charges to separate salt and pepper powder.

6. Pour some salt on a sheet of paper. Sprinkle some pepper on it. Can you separate the pepper from the salt? Bring a charged plastic ruler above the pepper and salt.The lighter pepper jump up more easily and most of the salt is left behind. Repeat this a few times and most of the pepper will be separated from slat.

Please refer to the link below - CBSE Class 8 Science Activity Mysterious Forces