P15 - Electromagnetism Flashcards
describe:
permanent magnet
- produces own magnetic field
- cannot be turned on or off
define:
induced magnet
a material made temporarily magnetic when placed in a magnetic field
describe:
interaction of an induced magnet and other magnets
the induced magnet is only attracted by other magnets, not repelled
What direction do magnetic field lines act in?
North to South
Where is the strongest magnetic field located on a magnet?
At the poles
What does the right hand grip rule show?
The direction magnetic field lines in concentric circles act in around a wire.
define:
solenoid
a coil of wire that produces a uniform magnetic field
desribe:
electromagnet
an iron core with a solenoid
list 3:
properties that determine an electromagnet’s strength
- turns in the wire
- current
- size of iron core
list 3:
uses of electromagnets
- recycling (sorting materials
- cranes
- electric bell
- relay
- circuit breakers
What is Flemming’s left hand used for?
motors
What does each finger represent in Flemming’s left hand rule?
thumb - motion (force)
first finger - magnetic field
second finger - current
formula:
force
on a wire in moters
F = BIL
force = magnetic flux density * current * length
N = T * A * m
define:
motor
a device that converts electrical energy into kinetic energy
explain:
How speakers work
Electromagnetic rod which moves back and forth based on a signal. Vibrations in the cone create pressure waves.
explain:
how an electric bell works
Uses an electromagnet to attract an arm to hit the bell. The arm moves and breaks its own circuit causing it to fall. This cycle repeats.
explain:
how a circuit breaker works
During a power surge, electromagnet becomes too strong causing a switch to open.
split ring commutator
switches the polarity of the current every half rotation
describe:
DC motor
- North and south pole magnet around a coil of wire.
- Current flows in opposite directions on either side of the coil.
- Creates opposite forces that spin the coil due to magnetic forces generated around the wire
- When the wire reaches a vertical position (half rotation), the split ring commutator switches the polarity of the current
- This causes the forces to be switched and the coil to be pulled down
- This means the coil rotates
What is Flemming’s right hand rule used for?
generators
What does each finger represent in Flemming’s right hand rule?
thumb - motion (force)
first finger - magnetic field
second finger - current
define:
generator
a device that converts kinetic energy into electrical energy
How common are naturally occuring magnetic materials?
very rare
define:
elctromagnetic induction
production of a voltage when a wire is moved through a magnetic field
explain:
elctromagnetic induction
A wire moves through a magnetic field so electrons insde the wire move as they align to the magnetic field lines. This induces a voltange, which could generate a current.
define:
transformer
device that increases or decreases voltage of an AC
What does P=IV show about transformers?
conservation of energy as voltage is just being converted into current
define:
primary and secondary coil
- primary - input
- secondary - output
number of turns proportion in a step up transformer
more turns on the secondary
taking a ‘step’ up - more
number of turns proportion in a step down transformer
less turns on the secondary
taking a ‘step’ down - less
formula:
number of turns and voltage
in primary and secondary coils
Vp / Vs = Np / Ns
describe:
dynamo (DC) generator
- a coil cuts magnetic field lines
- a potential difference is induced
- there is a complete circuit, so a current is induced
- each half-turn, the split ring commutator switchs contacts
- so the direction of the current does not reverse every half-turn
