Transcript P3 Revision - the Redhill Academy

P3 Electromagnetism
Revision
Electromagnetism
How do you make an electromagnet?
Insulated wire wrapped round a soft
iron core. When current applied a
magnetic field is produced.
Electromagnetism
How does a scrapyard crane work?
Current passed through
electromagnet, switches
magnet on, steel frame of
vehicles attach
Electromagnetism
How does a circuit breaker work ?
Switch held in place with iron
latch, when too much current
passes through electromagnet
it attracts the iron switch and
breaks circuit
Electromagnetism
How does an electric bell work?
Iron armature is pulled
onto the electro magnet,
breaks circuit, switching
off circuit, releasing
armature, cycle repeats
Electromagnetism
How does a relay work?
Current passes through
electromagnet, pulls
armature onto
electromagnet, armature
closes the switch gap and
switches on motor.
Electromagnetism
What is the motor effect?
The force produced
when a current in a
wire is passed
through a magnetic
field
Electromagnetism
How could you increase the size of the force in the
motor effect?
Increase the current,
increase the size of
the magnetic field
(bigger magnet).
Electromagnetism
Draw Fleming’s Left Hand rule and
label the fingers?
Electromagnetism
What happens to the force if you reverse the
current?
You reverse the direction of the
force.
Electromagnetism
What happens to the force if you reverse the
magnetic field?
You reverse the direction of the
force.
Electromagnetism
Describe how a loudspeaker works?
Current passes through
coil, force moves coil
forward, current changes
direction, force in
opposite direction moves
coil back in. Diaphragm
vibrates so much sound
waves are produced
Watch a video
Electromagnetism
Why does a loudspeaker work with ac
current?
The current needs to be changing
direction so the force also changes
direction. Direct current would
make the loudspeaker only move
out and stay there.
Electromagnetism
Describe how an electric motor works?
A current carrying coil
rotates in a magnetic field.
Force on each side of the
coil act in opposite
directions. Split ring
commutator reverses the
current so coil pushed in
same direction
Watch a video
Electromagnetism
What is electromagnetic induction?
Process of inducing a voltage
using a magnetic field
Electromagnetism
How is a voltage induced using a
magnetic field?
Conductor cuts the
lines of a magnetic
field, voltage induced
across the ends of
the conductor
Watch a video
Electromagnetism
Why are transformers useful?
They step up voltage from power
stations to reduce energy loss. They
also step down voltage so it is safe for
consumers. They reduce energy loss.
Electromagnetism
How does a transformer work?
Alternating current in
primary coil induces an
alternating magnetic
field which induces an
alternating voltage in
the secondary coils.
Electromagnetism
Why do transformers only work with
alternating current?
You need an alternating current to
produce the alternating magnetic
field that will induce ac in the
secondary coil.
Electromagnetism
What is a switch mode transformer?
Electromagnetism
Which devices use switch mode transformers?
Mobile phone chargers
Electromagnetism
In terms of percentages, how efficient are
transformers?
Almost 100%
Electromagnetism
Which equation shows in terms of power
that transformers are 100% efficient?
Vp x Ip = Vs x Is
Electromagnetism
Draw a step up and step down transformer
Notice that both of these are 100% efficient because power in = power out