Topic 6- Magnetism Flashcards
What can magnets do to other magnets and magnetic substances?
Magnets can attract other magnets if their poles are unalike or they can repel them if they are the same poles.
They can also attract magnetic substances.
What are the characteristics of magnetically hard materials?
Magnetically hard materials are materials such as steel. They keep their induced magnetism permanently as their domains remain aligned.
What are the characteristics of magnetically soft materials?
These are materials such as iron. They do not keep their magnetism permanently as their domains do not always remain aligned.
What is a magnetic field?
This is a region where magnetic materials will experience a force.
What are magnetic field lines?
These are invisible field lines that show the strength and direction of the magnetic field. The closer the lines are, the stronger the field is.
How can magnetism be induced?
By using a permanent magnet, you can induce magnetism on a magnetic material.
You can stroke the permanent magnet onto the magnetic material in one direction.
OR, you can place a magnet close to the magnetic material and it will induce its magnetism.
How can you investigate the magnetic field pattern for a bar magnet or between two bar magnets?
Place a bar magnet (or 2) on a piece of paper. Place several plotting compasses around the bar magnet and draw the direction of the compasses’ needle. (Field lines should go from N to S)
What happens when you put bar magnets with opposite poles together and what happens to the magnetic field lines?
The magnets will attract.
The filed lines between the opposite poles will be uniform and parallel, as of the two magnets were just one bar magnet.
What happens if an electric current is passed through a conductor?
An electric current in a conductor produces a magnetic field around the conductor.
The larger the electric current: the stronger the magnetic field.
The direction of the magnetic field depends on the direction of the current.
How are electromagnets made?
Wrap a wire around a soft core (e.g. Iron). Then, pass a current through the coiled-core and an electromagnet is made.
What are the magnetic field lines like for a straight wire?
The field around the wire is a simple circle. The direction of the filed lines depends on the direction of the current.
Using the right hand grip rule:
Current direction up: filed lines are anti-clockwise
Current direction down: field lines are clockwise.
What is the magnetic field pattern like for a flat circular coil?
The field around the flat coil is like a single wire, but with two circles- one for each direction.
What are the magnetic filed lines like for a solenoid?
- The magnetic filed inside the current carrying solenoid is strong and uniform.
- Outside the coil, the field is just like the one around a bar magnet.
Therefore, the ends of a solenoid act like the north and south poles of a magnet.
What happens to a charged particle when it moves in a magnetic field?
There is always a force on a charged particle when it moves in a magnetic field as long as the motion in the field is NOT parallel to the field lines.
(The force will be at its strongest if the charged particle is at 90 degrees to the field lines)
How do D.C motors work?
1) A d.c current is passed through a coil do wire which is able to move between two opposite magnetic poles.
2) When a current is passed through, the coil has a magnetic field which interrupts with the magnet’s magnetic field, =force= turn.
(Every half turn, the current changes so that the coil doesn’t come to a halt. This is done by using a split ring commutator)
How do loudspeakers work?
1) An a.c. current is passed into a coil of wire, which is wrapped around the base of the speaker.
2) The coil of wire is surrounded by permanent magnets, so depending on the direction of the current, a force on the coil is applied, either making it move backwards or forwards.
- these forward and backward movements make the cone vibrate=sound.
What is Flemming’s Left Hand rule and what does each finger represent?
Using the rule, we can predict the direction of the resulting force if we know 2 of the 3 directions.
Thumb: force
First finger: magnetic field
Second finger: direction of conventional current
How can you increase the force of a current carrying wire in a magnetic field?
You can do this by increasing the current or the strength of the magnetic field.
How can a voltage be induced in a magnetic field? How can the size of the voltage be increased?
Move a magnet through a coil of wire.
The size of the induced voltage can be increased by:
-using a stronger magnet
-increase the number of turns on the coil
-moving magnet faster
The direction of the induced voltage can be reversed by putting the other pole of the magnet through.
How do generators produce electricity?
Generators rotate a coil in a magnetic field (or a magnetic in a coil) and when either of these spin, lines of fields are cut- creating current.
Every half turn, the current changes direction, and with the help of slip rings and brushes, the contacts do not swap every half term too.
This means the current produced is A.C.
How do you increase the amount of current produced from a generator?
- Strength of magnetic field
- Number of coils in a wire
- speed of rotation in field
What is the structure of a transformer?
- Primary coil
- Secondary coil
- Iron core (to concentrate field lines= nearly 100% efficiency)
What do transformers do?
Transformers change the size of the voltage of an alternating current by having different a different number of turns on each of the input and output sides.
What are step up transformers?
These step the voltage up. They do this by having more turns on the secondary coil.
