Qualification > Reference Material
Physics P3 27/5/2010
J.Darren:
A reed switch is operated by a magnetic contact, when a piece of metal is brought near, the two contracts are ... well, in contact. When this arrangement is connected to a coil, it is connected to a circuit, hence when the two contacts are in contact, it completes the circuit and switches on, say a buzzer.
Another form of relay would be the magnetic relay.
http://www.irrigationtutorials.com/control1.gif
As shown above, when the switch is closed, the contact of the relay and the current with a pump is brought in contact, thus completing the output circuit (the one with a pump), it is then switched on. There is another form of relay where the contact is normally closed, and detaches when the switch is closed.
Circuit breaker
http://static.howstuffworks.com/gif/circuit-breaker-diagram.gif
The current flows through both terminals, this is an example of a normally closed relay as the contacts are normally closed. When the current gets strong enough, the pull from the electromagnet would release the iron catch, which detaches the contact and prevents current from going through. The switch is essentially a reset button which, by pressing it, enables you to close the contact again.
Magnetic field around a wire - Right hand grip rule (The fingers are pointed in the same direction as the magnetic field whereas your thumb is pointing in the direction of the current)
- The field lines are circles
- The field closest to the wire is the strongest
- Increasing the current would increase the overall field strength
A question from the 08 (?) Paper 3 asks what happens if there are two such magnetic field which interacts with each other. In this case they get attracted to each other.
Magnetic fields from coils - Right hand grip rule (Working out the poles - The direction which the thumb is pointing is the North pole, whereas the direction of your fingers represents the direction of the current)
- There are magnetic poles at both ends of the coil
- Increasing the number of turns in the solenoid increases the strength of the magnetic field
- Increasing the current increases the strength of the magnetic field
6394:
Thanks a looooooooooooooot kimo jesus
n j.darren
prayers 4 u =D
:) :) :) :)
realllllllyyyyyyyyyy help ful !!!!
:) ;) :D ;D ::)
J.Darren:
Magnetic force on a current - Fleming's left hand rule
Fleming's left hand rule
Thumb : Force
Index finger : Magnetic field
Field direction : North to south
The finger : Current
Current direction : Positive to negative
The wire moves across the magnetic field without being attracted to either poles.
- The produced force increases if a stronger magnet is used
- The produced force increases if the current is made stronger
- The produced force increases if the length of wire is increased
Ivo:
--- Quote from: J.Darren on May 23, 2010, 01:59:18 pm ---Magnetic force on a current - Fleming's left hand rule
Fleming's left hand rule
Thumb : Force
Index finger : Magnetic field
Field direction : North to south
The finger : Current
Current direction : Positive to negative
The wire moves across the magnetic field without being attracted to either poles.
- The produced force increases if a stronger magnet is used
- The produced force increases if the current is made stronger
- The produced force increases if the length of wire is increased
--- End quote ---
Easy way to remember FLHR:
First Finger: FIELD
SeCond Finger: CURRENT
ThuMb: Motion/Thrust
WARRIOR:
THANKS ALOT DAREN..YOU SAVED ALLOT OF MY TIME !!!! ILL ADD THOSE WHN ICOMPLTETE THE ECLECTRICTY NOTES 2NIGHT
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