View Full Version : Improvised compass
jacket of green 1
02-06-2005, 22:18
As any one have info on making a improvised compass - specifically "the rule of right hand twist" in the use of electricity for magnetising a needles? :confused:
Ogri the trog
02-06-2005, 23:12
From what little I can remember from school,
A needle can be magnetised by stroking it in one direction for a short time with another metalic object. You can then suspend the needle from a long thread to allow it to swing North/South, ( I'd try several times before relying on it). Better is to float it on the surface of some still water (billy can for example).
Despite this, there are various other methods of determining North without resorting to dubious skills of metalurgy!
Sun, stars, wind direction, river travell etc - though most rely on you knowing the basic lay of the land over which you are travelling.
ATB
Ogri the trog
Tantalus
02-06-2005, 23:32
i seem to remember being told at school that if you line up a piece of metal with north and give it a good belt with a hammer it will magnetise it. not strongly magnetised but enough for it to be able to point north when hung from a thread
anyone know if this works?
Tant
Dr Adam Heart-Davis demonstrated making a compass using a needle and a rock (or should that be stone since it was a tool).
Anyway, it's quick easy and simple, hold the needle in one hand up right and hit it gently on the end with a rock/stone, after a minute or so of this you have a magnetic needle. He floated it on a leaf in a pot of water.
He then showed a clip from a TV programme where he held up a very big heavy magnet that could holdit's own weight that had been magnatised purely by hitting it reapeatedly.
Jacket of green.. is that a clue ?. Anyway from what i can remember any improvised compass should be cheked against another method to determine its accuracy. I'm not sure about the right hand twist thing. I'm an Ex "halfer"
just noticed tant got there before me
in the lecture the needle was just put on the table poiting up and tapped a bit, no mention of having to point it north to start off with. You wont know which end is north but north from south shouldn't be too much trouble, I normaly just check the trees for the side that has most growth(south).
steven andrews
21-10-2005, 11:42
At school we magnetized a needle with a magnet and then sat it in some water on a piece of tissue paper. When you gently poke the tissue paper it sinks, leaving the needle sitting on the surface-tension of the water, pointing North/South.
I recently showed my daugther this - she was impressed with the needle floating on the water - not that interested in the North/South bit! :rolleyes:
innocent bystander
21-10-2005, 11:50
right hand twist - is that for electromagnets ??
gregorach
21-10-2005, 12:00
The right-hand twist rule tells you the direction of a magnetic field around a straight wire with a current flowing through it - if your thumb is pointing in the direction of conventional current, then the field twists around the wire in the direction of your fingers. Just to confuse matters, conventional current is the opposite of real current.
I'm not sure what use it would be for making an improvised compass, but it can be used to demonstrate the principles of an electric motor.
innocent bystander
21-10-2005, 12:12
That rings a bell. A verry dim, distant bell... :lmao:
At school we magnetized a needle with a magnet and then sat it in some water on a piece of tissue paper. When you gently poke the tissue paper it sinks, leaving the needle sitting on the surface-tension of the water, pointing North/South.
I recently showed my daugther this - she was impressed with the needle floating on the water - not that interested in the North/South bit! :rolleyes:
That is a good trick! I just tried the floating bit with a needle. I didn't use the tissue paper idea, I just dropped the needle on the surface from about 1/4 inch up (you could tell how close by the reflection).
It then proceeded to align itself North South.
Not that Taz
30-10-2005, 18:14
MAYDAY - Electronics Engineer loose in the Forum. Prepared to be bored.
The Right Hand Rule is one of the best rules in electromagnetism as it's a) versatile and b) I can actually remember it.
It applies to (as someone has said) direction of field and current. If the field is in the direction your thumb points, then the induced current in a coil goes in the direction of you fingers. Also applies to a moving piece of ferrous metal. An iron bar moving through a coil in the direction of your thumb will induce a current in the direction of your fingers.
Best of all, it applies to which way you turn a screwdriver, because that I can never remember!
You can wake up now.
Not sure how you can really apply it to manufacture of a usable improvised compass. I'm with the rest of the guys.... hit it with a rock, then drop it into water... hanging off threads is usally tricky unless you tie it exactly in the middle.
Taz - the Boring One.
Biddlesby
30-10-2005, 22:20
The above method relies on your hands being at right angles to each other. Point your first finger as if you were pointing at somebody, then your thumb straight upwards. Finally, your second finger should point in the only direction left (think of x, y, z). Remember that first finger is flux (the magnetic field), second finger is current (conventional) and thumb is thrust (movement).
Finally, another thing to remember is that when looking head on, for example, to a wire, flux will flow around it in the direction which you screw a corkscrew.
There are other applications of the right hand rule in vectors.
Personally I'd agree with Taz on the subject of suspending needls from thread....
Newtons right hand rule for motors I believe
The same applies for the left hand rule for generators
Thinking about it, in may be Faradays r+l hand rule
I'm just back from the pub and am wishing I had not clicked on this thread.....Jon
Not that Taz
20-11-2005, 10:47
Oops....
Sorry to have instigated a "Pub Ruining Sesh" Jon :lmao:
Taz
Not being drawn on differences between Right Hand Rule, Righ and Left hand corkscrew rules.......