P 13-electromagnetism Flashcards
(20 cards)
Magentism
-the ends kf magnets are called poles
-magnets have two poles-north and south
-when two magnets are held close together, there will be an attractive or repulsive force brtween the magnets depending on how they are arranged
Law of magnetism states:
-two like poles repel each other
-two unlike poles attract each other
-the attraction or repulsion between two magnetic poles is an example of s non-contact force
Magnetic material
Magnetic materials are attracted to magnet:
-iron,steel,cobalt and nickel
Non-magnetic materials are not attracted to a magnet:
-zinc,magnesium,copper,gold,silver,aluminium
-steel is an alloy which contains iron, so is also magnetic
-magnetic materials will always be attracted to magnet,regardless of which pole is held close together
-to test wether a material is a magnet should be brought close together to a known magnet:
-if it can be repelled by known magnet then material itself is a magnet
-if it can inly be attracted and not repelled then its a magnetic materisl
Permanent magnet
-permanent magnet are made out of permanent magnetic materials, for example steel
-a permanent magnet will produce its own magnetic field
It will not lose its magnetism
Induced magnets
-when a magnetic material is placed in a magnetic field, the material can temporarily be turned into s magnet-induced magnetism
-when magnetism is induced on magnetic material:
One end of material will become north pole and other end will become south pole
-magnetic materials will always be attracted to permanent magnet
This means that the end of material closest to magnet will have opposite pole to magnets pole closest to material
Magnetic fields
-all magnets are surrounded by magnetic field
-defined as the region around a magnet where a force acts on another magnet or on a magnetic material (such as iron,steel,cobalt and nickel)
Magnetic field lines
-are used to represent strength and direction of a magnetic field
-the direction of magnetic field it is shown using arrows
-the strength kf magnetic field is shown by spacing of magnetic field line
If the magnetic field lines are close together then the magnetic field will be strong
If they are far apart 5e magnetic field will be weak
-there are some rules when drawing magnetic field line:
Always go from north to south
Must never touch or cross field lines
Magnetic field in a bar magnet
-the magnetic field is strongest at poles-where the magnetic field lines are closest together
-magnetic field becomes weaker as the distance from magnet increases
-because field lines are getting further apart
Force of attraction
An attractive force can experienced between:
-the opposite poles of two different permanent magnets
-a magnet and a magnetic material due to induced magnetism
-a magnetic will always induce the opposite pole in closest end of magnetic material
Uniform magnetic field
-a uniform magnetic field will be produced in gaps between opposite poles
-a uniform magnetic field is one that has same strength and direction at all points:
To show that the magnetic field has same strength at all points there must be equal spacing brtween magnetic field lines
Same direction at all points show by arrow on each magnetic field line going from north to south pole
Representing magnetic fields
-direction of magnetic field at any point is given by direction of force that would act on another north pole placed at the point
-the direction of a magnetic field line is from north to south pole of magnetic-because north pole would be repelled by north pole and attracted by south pole of magnet
Plotting magnetic fields:
-shape and directions of magnetic field may be investigated using plotting compasses
-a plotting compass is like a small bar magnet,with a north and south pole
-arrow of the plotting compass represents north pole
Investigating the shape and direction of a magnetic field
Step1:
-place the magnet on top of piece of paper
-draw a dot at one end of magnet near the corner
Step 2:
-place a plotting compass next to the dot, so that one end of the needle of compass points away from dot
-use a pencil to draw a net dot at other side of the compass needle
Step 3-move the compass so that it points away from new dot, and repeat process above
Step 4-keep repeating the previous process until there is a chain of dots going from one end of magnet to other
-remove the compass, and link the dots using a smooth curve-this will be the magnetic field line
Step 5:
-repeat the whole process several times to create several other magnetic field lines
Earth’s magnetic field
-on earth, in absence of any magnet or magnetic materials, a magnetic compass will always point north-evidence that core of earth js magnetic and creates its own magnetic field
-on earth, the north arrow on a magnetic compass will point towards geographical north pole
Because geographical north pole is a magnetic south pole
The north pole of magnetic compass is attracted to earth’s magnetic south pole
The geographical south pole is a magnetic north pole
-the north pole of magnetic compass is repelled from earth’s magnetic north pole
Magnetic field around a wire
-when a current flows through a conducting wire a magnetic field is produced around the wire
A conducting wire is any wire that has a current flowing through it
-the shape and direction of a magnetic field can be investigated using plotting compasses
-the magnetic field is made up of concentric circles
A circular field pattern indicates that the magnetic field around a current-carrying wire has no poles
-as the distance from the wire increases the circles get further apart
This shows that the magnetic field is strongest closest to the wire snd gets weaker ss the distance frkm the wire increases
The right hand thumb rule can be used to work out the direction of magnetic field
Reversing the direction in which the current flows through the wire will reverse the direction of the magnetic field
-if there is no current flowing through the conductor there will be no magnetic field
-increasing the amount of current flowing through the wire will increase the strength kf the magnetic field so the field lines will be closer together
Magnetic field around a solenoid
-when a wire is looped into a coil, the magnetic field lines circle around each part of the coil,passing through centre of it
-to increase the strength lf the magnetic field around the wire it should be coiled to form a solenoid
-the magnetic field around the solenoid is similar to that bar of a magnet
-the magnetic field inside the solenoid is strong and uniform
-one end of the solenoid behaves like the north pole of magnet and other side behaves like south pol
To work out the polarity of each end the solenoid it needed to be viewed from the end
If the current js travelling around in clockwise direction then it is south pole
If the current is travelling around in an anticlockwise direction then it is north pole
-if the current changes direction then the north and south poles will be reversed
-if there is no current flowing through wire then there will be no magnetic field produced around or through solenoid
Magnetic field strength around solenoid
Strength of magnetic field around solenoid can be increased by:
-increasing the size of current which is flowing through wire
-increasing the number of turns in the coil in a given length
-reducing the length of the wire and maintaining number of turns
-adding a iron core through the centre kf coils
-the iron core will become induced magnet when current is flowing through coilds
-the magnetic field produced from solenoid and iron core will create s much stronger magnet overall
Electromagnets
-electromagnet is a solenoid with an iron core
-the magnetic field produced by electromagnet can be switched on or off
When a current is flowing there will bd a magnetic field produced around the electromagnet
When the current is switched off there will be no magnetic field produced
Strength of electromagnet can be changed by:
-increasing the current will increase the magnetic field produced around electromagnet
-opposite will happen if current is decreased
The motor effect
Occurs when-a wire with a current flowing through it is placed in a magnetic field and experiences s force
-this effect is a result of two interacting magnetic fields
One is produced around a wire due to the current flowing through it
The second is the magnetic field into which the wire is placed
-as a result of the interactions of 2 magnetic fields, the wire will experience a force
Factors affecting force on motor effect
-the size if the force exerted by magnetic field increased by:
-increasing the amount of current flowing through wire which will increase magnetic field around wire
-using stringer magnets which will increase magnetic field between poles of the magnet
-placing the wire at 90 degrees to the direction of the magnetic field lines between the poles of the magnet as will result in maximum interactions between 2 magnetic fields
Calculating magnetic force on a current-carrying conductor
F=BIL
F=force=N
B=magnetic flux density=Tesla T
I=current=A
L=length=m
Fleming left hand rule
Thumb=force
First finger=field
Second finger= current
