Charge

These early experiments with static electricity showed that there are two types of charge, which were called positive and negative. Two rods that are charged positively repel each other, i.e. push apart from each other. However, when a positively charged rod is brought near a negatively charged rod they attract, i.e. there is a force of attraction.

• Like charges repel
• Unlike charges attract

Children are very aware of the existence of lightning! (It would be very interesting to find out what the children think is going on in a thunderstorm). A touch of science can be very reassuring here: The lightning and the thunder actually occur at exactly the same time. It is a huge spark or discharge of energy, and if you hear the thunder, then you know that you are safe - the immediate danger is past! There is a time delay between the lightning and the thunder because light travels faster than sound. If the lightning is seen at the same time as the thunder is heard, then you are at the very centre of the storm and exactly where the lightning strikes. Lightning will discharge at the sharpest, highest point so it is safest to lie down by a hedge and certainly do not take shelter under a tree!

Church steeples usually have lightning conductors fitted to them so that if they are struck by lightning, the electricity is safely discharged to the ground. Again friction is involved in this phenomenon. Clouds are formed as water droplets rise because of evaporation and these droplets rub against the atoms in the air and become charged.

Recipe for a Fried Scientist:

When batteries were first discovered, some brave or foolhardy scientists decided to experiment to find out if the current batteries produce is basically the same phenomenon as that in lightning. Benjamin Franklin was the man who first tried this out and, rather surprisingly, he lived to tell the tale! He flew a kite in a storm so that it was struck by lightning and observed the almighty spark produced in a gap at the bottom of the thread (unlike the man in the cartoon, he did not hold the thread!). This spark was identical to one produced by a large voltage battery and the experiment was successful. Two other scientist tried a similar experiment and were not so lucky and died in the attempt. This is definitely not one to try at home or even mention to children!

Contents

Safety, Static Electricity
Current Electricity, Making a bulb light, Models
Atomic Theory
Conductors and insulators
Switches, Short circuits, Circuit diagrams
Current, Voltage
Electrical circuits
Measuring current
Resistance
Power
Assessment/Discussion Material
Reference Material