P15 Flashcards
All magnets produce a magnetic field
A region where other magnets or magnetic materials experience a force.
The lines on a mgneric field diagram only go from
North to south
The closer the lines are together,
The stronger the magnetic field. The further away from a magnet you get, the weaker the field is
The magnetic fiekd is strongest
.at the poles of a magnet. This means that the magnetic forces are also strongest at the poles.
The force between a magnet and a magnetic material is always
attractive, mo matter the pole.
If two poles of a magnet are put near each other
They will each exert a force on each other. The force csn be attractive or repulsive. Two poles that are the same will repel each other, two unlike poles will attract each other
What are the gs that can effect the power of the electromagnet
- the core material
- number of coils
- size of the current
Inside a compass is a tiny
- ## Bar magnet. The north pole of this magnet is attracted to the south pole of any other magnet it is near.
You can move a compass around a magnet and trace
Its position on some paper to build up a picture of what the magnetic field it is in
When they aren’t near a compass
It always points north. This is because the earth generates its own magnetic field, which shows the inside of the earth must be magnetic
There are two types of magnet
Permanent and induced
Permanent magnet
Produce their own magnetic field
Induced magnets
Are magnetic materials that turn into a magnet when they’re put into a magnetic field.
The force between permanent and induced magnets is always attractive.
When you take away the magnetic field, Induced magnets
quickly lose their magnestusn and stop producing a magnetic field
Slide 12 on 15.1 for diagram
- When the current flows through the
circuit, the electromagnet makes a
magnetic field. - The electromagnet attracts the
springy metal arm. - The arm hits the gong, which
makes a sound. - The circuit is broken now the arm is
out of position. - The electromagnet is turned off and
the springy metal arm moves back. - The circuit is complete again.
- The cycle repeats as long as the
switch is closed.
When a current flows through a wire
A magnetic field is created around the wire.
- the field is made up of concentric circles perdendicular to wire with wire in middle (cgp 93)
- you can see this by placing a compass near a wire, that is carrying a current. As u move the compass, it will trace the direction of the magnetic field
When a current-carrying wire is put between magnetic poles, the magnetic field around the wire interacts with rhe magnetic field it has been placed in. This causes the magnet and the conductornto exert a force on each other. This isncalled the
Motor effect and and can cause the wire to move.
Force, magnetic flux density, length, current
Force (N) = magnetic flux density (T,tesla) x Current (A) x length(m)
F. =. B. X. i. X. L
How does a motor work?
Forces act on the two side arms of a coil of wire that’s carrying a current. These forces are just the usual forces which act on any current in a magnetic field. Because the coil is on a spindle and the forces act one up and one down, it rotates. The split-ring commutator is a clever way of swapping the contacts every half turn to keep the motor rotating in the same direction. The direction of the motor can be reversed either by swapping the polarity of the dc supply (reversing the current) or swapping rhe magnetic ooles over (reversing the field).
Generator effect
The induction of a pd (and current if there’s a complete circuit) in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field.
The generator effect, how to get it
You can do thid by moving s mahnet in a coul of wire or moving a conductor in a magnetic field. Shfiting the magnet from side to side creates a little blip of current if the conductor is part of a complete circuit.
If you move the magnet in the opposite direcrion, then the pd/currentwill be reversed. Likewise if the polarity or the magnet is reversed, then the potential difference /current will be reversed too.
If you keep the magnet moving backwards and forwards, you produce a potential difference that keeps swapping direction- an alternating current.
- no current is generated when wire is stationary.
If your looking at a solenoid end and the current is clockwise, the pole is
South
If your looking at the end of the solenoid, and the current is travelling anticlockwise
Its at the north pole
STEP-UP TRANSFORMERS
Step the potential difference up. They have more turns on the secondary coil than the primary coil
STEP-DOWN TRANSFORMERSA
Step the potential difference down. They have more turns on the primary coil than the secondary.
