Magnets paper 2 Flashcards
What are magnets ?
Any material or object that produces a magnetic field
What is a magnetic field?
An invisible region around a magnet where another magnet will experience a force
Which way do the magnetic lines always go?
From north to south
The magnetic field liknes show which way a force would act on a north pole at that point in the field
When are magnets strongest?
The closer together the lines are, the stronger the magnetic field
The further away from a magnet you get the weaker the magnetic field
The magnetic field is the strongest at the poles and magnetic forces
When will a magnet be attractive or replulsive?
Two poles that are the same (like poles) will repel
Two poles that are different (unlike poles) will attract each other
What is a uniform field?
Where the magnetic field is the same strenghth everywhere between the poles
It can be created by placing the north and south poles of two bar magnets near each other
How does a compass find field lines?
Inside a compass is a tiny bar magnet called a needle. A compass magnet always lines up with the magnetic field it’s in
What is magnetic material and give examples?
Magnetic material is any object that can be influenced by magnetic fields and has a potential to become a magnet
The main three magnetic elements are iron, nickel and cobalt
Some alloys and compounds of these metals are also magnetic like steel as it contains iron
What happens when you put a magnetic material near a magnet
Its alway attracted
Whats a permenant magnet?
(e.g. bar magnets)
Produce their own magnetic fields all the time
What is a induced magnet?
Induced (temporary) magnets only produce a magnetic field while their in another magnetic field
This magnetic induction explains why force between a magnet and a magnetic fieldis always attractive - the south pole of a magnet induces with a north pole of a magnet
And if you take away the magnetic fied, induced magnets return to normal and stop producing a magnetic fields
How quickly do magnets lose their magnetism depending on their material
Magnetically ‘soft’ materials e.g. pure iron and nickel-iron alloys lose their magnetism very quickly
Magnetically ‘hard’ materials e.g. steel lose their magnetism very slowly
Permenant magnets are made from magnetically hard materials
What is electromagnetism
A moving charge creates a magnetic field
When a current flows through a long straight conductor (e.g a wire) a magnetic field is created around it
The field is made up of concentric circles perpendicular to the wire in the centre
What does changing the direction of a current do?
It changes the direction of the magnetic field
How can you find out the magnetic fields direction?
Use the right hand thumb rule to work out which way it goes
How can you increase the strength of a magnetic field?
By wrapping a length of wire into a long coil with lot’s of loops called a solenoid
Inside a solenoid you get lots of field lines pointing in the same direction. The magnetic field is strong and almost uniform
Outside of the coil, the overlapping field lines cancel each other out so thr field is weak
What is a solenoid?
An example of an elecromagnet - a magnet with a magnetic field that can be turned on and off
Ways to increase the strength of an electromagnet
-Increase the current
-Increase the number of turns in the solenoid, while keeping the lenght the same
-Reduce the length of the solenoid while keeping the number of turns the same
-Putting a block of iron in the centre of the coil. This iron core becomes a induced magnet, whenever current flows
What is the motor effect?
A current carrying wire in the pressence of a magnetic field will experience a force
To experience the full force, the wire has to be at 90 degrees to the magnetic field
If the wire runs along the magnetic field ir won’t experience a force at all. At angles in between it’ll feel some force
What happens if you change the direction of the current?
The force always act in the same direction relative to the mahnrtic field and direction of the current so changing either the magnetic field or direction the current will also change
What is Flemings left hand rule
Point your first finger in the direction of the magnetic field
Point your second finger in the direction of the current
Your thumb will then point in the direction of the force
Equation related to force
Force = magnetic flux density x current x length
