Electromagnetic effects Flashcards
What always have magnetic fields around them?
current carrying conductors or moving electrons
What is the pattern of a magnetic field in straight wires?
circular and perpendicular to the wire, getting weaker with distance
How can you find the direction of a magnetic field in straight wires?
Right hand grip rule n1: your thumb is conventional current, and the rest of your fingers are the magnetic field direction
How do you know if the conventional current is going into or out of the paper?
cross: current into the page
dot: current out of the page
In a single wire, how can you increase the strength of the magnetic field?
greater current
What is the direction/pattern of the magnetic field in a solenoid?
the same as in a bar magnet
What is the relationship between current and direction of magnetic field on a solenoid?
the general direction of the current flow indicates the direction of the magnetic field
How can you find out the direction of the magnetic field in a solenoid?
right hand grip rule n2: your thumb points to the the north pole, the rest of your fingers are conventional current
How can you reverse magnetic field direction in a solenoid?
- reverse current/cell
- wrap wire in opposite direction
How can you increase the strength of the magnet in a solenoid?
- more turns of coil
- more current
- wrap wire on an iron core
Describe an experiment to identify the pattern/direction of a magnetic field in straight wires and solenoids.
- use a compass to determine the direction of a field at a single point
- draw an arrow in the direction of the field
- move the compass to different points and repeat
- you will have a diagram of the magnetic field
What is a relay?
electromagnetic switch, a circuit with a small current turns on another circuit with a large current
How does a relay work?
- switch is closed
- small current magnetised the coil
- iron reeds are attracted and close
- large current flows
What is the energy conversion in a loudspeaker?
it converts electrical energy into sound energy
How does a loudspeaker work?
- alternating current in coil creates an alternating magnetic field in coil
- this alternating magnetic field will interact with the permanent magnetic field
- this interaction will make the papercone move in/out producing sound waves
If you use high frequency ac in a loudspeaker, what will happen?
high frequency sound waves
If you use large voltage ac in a loudspeaker, what will happen?
loud sound waves
Why are relays useful?
the turn on larger current circuit by turning on a smaller current circuit: this way, we do not need to use thick, heavy, expensive cables to carry the large current
What happens if you supply a solenoid with AC?
the current will change, so the direction of the magnetic field will also change every half cycle
What is the variation of magnetic field strength in straight wires?
strongest closest to wire
What is the variation of magnetic field strength in solenoids?
uniform magnetic field inside coil
What happens if you increase the size of the current in a straight wire?
results in a stronger magnetic field
What happens if you increase the size of the current in a solenoid?
results in a stronger magnetic field
What happens if you reverse the current in a solenoid?
reverses magnetic field direction
What happens if you reverse the current in a straight wire?
reverses magnetic field direction
What happens whenever a current is at a right angle to a magnetic field?
it experiences a force, perpendicular to both the current and magnetic field
Why is a force experienced when a current carrying conductor is in a magnetic field?
interaction between the current’s magnetic field and the permanent magnetic field
How can we work out the direction of the force when there is a current carrying conductor in a magnetic field?
Fleming’s left hand rule:
First finger is magnetic field (N to S)
Second finger is conventional current
Thumb is the thrust/force