magnetism Flashcards
Magnetic field
A region where other magnets or magnetic materials experience a force
What are the four magnetic materials?
=> Iron
=> Steel
=> Nickel
=> Cobalt
In which direction do magnetic field lines go?
From north to south pole
What do close together magnetic field lines mean?
Stronger
Where is the magnetic field the strongest?
Poles
What is the force between magnet and magnetic material always?
Attractive, no matter the pole
What will happen to like poles?
Repel
What will happen to different poles?
Attract
What do compasses show and why?
Direction of magnetic fields, since there is a bar magnet inside
Permanent magnets
Produce their own magnetic field
Induced magnets
Magnetic materials that turn into a magnet when they are put into a magnetic field
What does a moving charge create?
A magnetic field which is made up of concentric circles
How do you work out the magnetic field direction of a wire with moving charge?
Right-hand grip
How to change the strength of magnetic field in a wire?
Changes in current and distance from the wire
What is a solenoid?
A coil of wire
What does the loop of wire, which line up with each other, result in?
Field lines pointing in the same direction that are very close to each other
What are magnetic field lines inside a solenoid like?
Strong and uniform (it has the same strength and direction at every point in that region)
https://physics.stackexchange.com/questions/323326/why-do-magnetic-field-lines-point-towards-the-north-pole-on-the-inside-of-a-sole
How can you increase the magnetic field in a solenoid?
Putting a block of iron in the centre of the coil
Electromagnet
A type of magnet in which the magnetic field is produced by an electric current.
What are the two uses of electromagnets?-
=> Scrap yards, to pick up stuff
=> Used within other circuits to act as switches:
- attracts iron contact on the rocker
- rocker pivots and closes the contacts, completing circuit two, and turning on the motor
Motor Effect
A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles. This is called the motor effect.
In what position does the wire has to be for it to experience the full force?
90°
What is the equation to find the force acting on a conductor in a magnetic field?
F= B (magnetic flux density (T, tesla)) x I (current (A)) x l (Length (m))
Fleming’s left-hand rule
First finger => Field
Second finger => Current
Thumb => Force (Motion)
How can the direction of the motor be reversed?
Swapping polarity of the dc supply or swapping the magnetic poles over
What do loudspeakers and headphones use?
Electromagnets
Loudspeakers
- a current in the coil creates a magnetic field
- the magnetic field interacts with the permanent magnet generating a force, which pushes the cone outwards
- the current is made to flow in the opposite direction
- the direction of the magnetic field reverses
- the force on the cone now pulls it back in
- repeatedly alternating the current direction makes the cone vibrate in and out
- the cone vibrations cause pressure variations in the air - which are sound waves
Generator Effect
When motion between a conductor and a magnetic field creates electricity, ie a magnet is moved into a coil of wire.
How can you produce the generator effect?
Moving a magnet in a coil of wire OR moving a conductor in a magnetic field (cutting magnetic field lines)
What will happen if you move the magnet in the opposite direction in the generator effect?
The potential difference/current will be reversed
How do you produce an alternating current by the generator effect?
Keep the magnet moving backwards and forwards, which produces a potential difference that keeps swapping direction
What does the magnetic field created by an induced current always do?
Acts against the change that made it (wether that is the movement of a wire or a change in the field it is in)
How can you increase induced potential difference by doing two things?
=> Increasing the speed of the movement - cutting more magnetic field lines in a given time
=> Increasing the strength of the magnetic field
What do alternators generate?
An alternating current
What do alternators use so the contacts do not swap every half term?
Slip rings and brushes
What does the alternator produce?
An alternating potential difference
What do dynamos generator?
A direct current
What do dynamos use so the connections are swapped every half turn to keep the current flowing in the same direction?
Split-ring commutators
What can you use to see the generated potential difference?
An oscilloscope
Microphone
1) Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet
2) This causes the coil of wire to move in the magnetic field, which generates a current
3) The movement of the coil (and so the generated current) depends on the properties of the sound wave (louder sounds make the diaphragm move further)
4) This is how microphones can convert the pressure variations of a sound wave into variations in current in an electric circuit
What do transformers change the pd for?
Only for alternating current
Step-down transformers
Step the PD down. They have more turns on the primary coil than the secondary coil
Why does the national grid uses low currents?
Less energy is wasted heating the wires and the surroundings
