Compasses D. Crowley, 2008. Compasses To understand how compasses work Wednesday, August 05, 2015.
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Transcript of Compasses D. Crowley, 2008. Compasses To understand how compasses work Wednesday, August 05, 2015.
Ocean Imagine you are stuck out at sea – every direction you look,
you see nothing but deep blue sea and it is overcast so you cannot tell the position of the Sun…
How could you work out which way to travel?
Compass No matter where you stand on Earth, you can hold a compass
in your hand and it will point toward the North pole
A magnetic compass consists of a small, lightweight magnet balanced on a nearly frictionless pivot point
The Earth does not contain a giant bar magnet, but it behaves as if it does - the Earth has a magnetic north pole and a magnetic south pole
Compasses work because bar magnets can line up in the Earth's magnetic field and point north
Magnetic The North pole of a bar
magnet is actually called the ‘North-seeking pole', and it points to the Earth's magnetic North pole
The South pole of a bar magnet is actually called the ‘South-seeking pole', and it points to the Earth's magnetic South pole
Compasses point towards the Earth’s magnetic North pole
Plotting Compasses Small compasses called plotting compasses can be used to
show the magnetic field around a bar magnet, instead of using iron filings
The needle in each compass turns and lines up along the field lines
Plotting Compasses If we arrange some plotting compasses around a bar magnet,
we see that the needles point away from the magnet's north pole and towards its south pole
Magnet How could you design you own compass if you were stranded
on the boat in the middle of the ocean?
You have luckily brought your favourite magnet with you!
Making Magnet Remember, a magnet can be made by magnetising a material
which is attracted to a magnet, e.g. a paper clip
There are three methods that can be used to make a magnet: -• Stroke a magnet along the paperclip from one end to the
other and then starting from the same place, repeat the movement - the more times this is done, the more magnetic the clip becomes
• Hold a nail in a magnetic field and hit it with a hammer• Put a magnetic material in a strong magnetic field
Magnet To make the magnet you will need: -
A needle or some other wire-like piece of steel (e.g. a straightened paper clip)
Something small that floats such as a piece of cork, the bottom of a Styrofoam coffee cup, a piece of plastic or the cap from a milk jug
A dish, preferably a pie plate 23 - 30 cm in diameter, with about 2.5 cm of water in it
Step 1 Turn the needle into a magnet – stroke a magnet along the
needle 20-30 times in the same direction
Step 2 Place you float in the middle of the dish – the float on water
creates a nearly frictionless bearing, vital for a compass to work as the magnetic field of the Earth is quite weak at the surface