Electromagnetism Flashcards
What is created around a current carrying conductor
A magnetic field
Which hand rule do we use to determine direction of a current
Right hand grip rule (search it up to fully learn)
What does a circle with a small black circle in it mean
Current coming out (of the page)
What does a circle with a cross in it mean in electromagnetism (looks like the symbol for a bulb)
Current going in (to the page)
What do the fingers mean in Flemings left hand rule, from top down if orientated with the thumb facing up (normal orientation)
Thumb - force
Index finger - magnetic field
Middle finger - current
FBI
How does a magnetic field interact around a current-carrying conductor
The magnetic field goes around it
Does the magnetic field go N-S or S-N
North - South
Do magnetic field lines ever overlap or touch
No
What is essentially an electric current
A moving POSITIVE charge
Does a moving charge experience a magnetic force
Yes
What hand rule is used for moving charges in magnetic fields
Flemings LH rule
What is Flemings LHR used for
Finding the direction of force, magnetic field and current for an electromagnet
If a charged particle moves parallel to a magnetic field, what os the effect on the trajectory of the charged particle
There is no magnetic force so it continues in a straight line
Do electrons flow in the same way or opposite to the electric current
Opposite
What direction is the force on a moving electron in a magnetic field
Opposite direction to a positive charge
What letter is used to indicate magnetic fields
B
How does a loudspeaker work
When the current flows through the coil in one direction, this creates a magnetic field, which interacts with the permanent magnetic field, creating a force which causes the cardboard cone to move in one direction. When the current changes direction, the cone moves in the opposite direction, creating sound waves.
Why do loudspeakers use a ‘varying alternating current’?
It must have force in both directions, so it needs to change the direction of current and the magnitude of the permanent magnetic field, which creates the force.
What happens to the current in a loudspeaker when the sound gets louder (bigger vibrations)
It increases in magnitude
What is the magnetic field around a direct current (d.c.) motor?
The same size and direction
Which way does current flow
+ to -
What does the split ring commutator do
Reverses the direction of the current every half turn of the coil
See the split ring commutators diagram
Ok
What do magnets do in relation to other magnets
They repel like poles and attract unlike poles
What do magnets do to magnetic substances
Attract them
What is a magnetically ‘hard’ material
It retains any induced magnetic properties
What are magnetically ‘soft’ materials
Materials that can lose any induced magnetism
What type of core is used in electromagnets
Soft iron cores
How can you make an electromagnet stronger (4)
- Increase the current
- Increase the number of turns in the coil
- Densely pack the coil
- Add a soft iron core
How is a electromagnet constructed
A wire is coiled around a soft iron core
What is the right hand rule
Grab a single wire with your thumb aligned with the conventional current, your fingers will show you the direction of the magnetic field
What is conventional current
Positive to negative
What happens to some objects when they are placed in a magnetic field and what are these objects called
They can become magnetic. They are referred to as being magnetically ‘soft’
Can magnetic field lines cross
No
How do you find the magnetic field pattern for a bar magnet
Iron filings method - sprinkle iron filings on a piece of paper above a bar magnet, then the filings will make the lines. Then draw the lines on the paper.
Compass method - put many compasses around the magnet - the direction of the needles will show the direction of the field lines - then draw the lines
What does an electric current going through a conductor produce
A magnetic field
What is the magnetic field for a flat circular coil when carrying current
Circles around each side (see google)
What is the magnetic field lines for a solenoid (coiled up wire) when carrying current
Passing through the coil and one on the outside on each side (see google)
What is the magnetic field of a wire when carrying a current
A circle (use right hand rule for direction)
Can magnets be charged
No
What direction do magnetic field lines go
North to South
What direction does convection current flow
+ to -
What direction do electrons flow
- to +
