Year 9 Physics practical
This was an amazing experiment. We are learning about electrical charges. This isn't in our Physics book.
It's called Kelvin's Dropper, and it's a Hydrostatic Generator. It was invented by Lord Kelvin in the 19th Century.
How does it work?
Water is added to the white plastic tank at the top which we made by cutting a hole in a milk jug.
It then falls out as streams of water through the two glass droppers.
The two glass jars lined with foil are simple CAPACITORS. Because they are insulated from each other they must have a slightly different charge. The left jar is connected to the copper ring on the right, the right jar to the left ring. These are collectors.
As the water passes through a ring, charges in the ring REPEL the same charges in the water, pushing them back up into the tank, and ATTRACT the opposite charges downwards.
When the drop breaks off it carries this opposite charge into the jar (capacitor) below, where it is stored.
The same thing happens on the other side.
So, if left ring is slightly POSITIVE, it will attract negative charges down and push positive charges up. The drop that falls into the jar below will now have a NEGATIVE charge.
The opposite happens on the right side.
Each drop adds more and more CHARGE to the jar below.
When the charge difference between the two jars is high enough, a spark jumps across a gap between two paper clips! This exactly what happens in a thunderstorm.
It was really difficult to get to work well, you must make sure everything is very well INSULATED to stop the charges leaking away.
Eventually we got a spark 3mm long! We looked up SECONDARY SOURCES on the internet and it said a 3mm spark is over 2,000 volts!!!
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