Topic 13 - Electromagnetic induction Flashcards
Electromagnetic induction is
The induction of a potential difference in a wire which is experiencing a change in magnetic field
When magnetic field lines are cut through
A potential difference is induced in a conductor
If the conductor moves back and forth in a magnetic field
An alternating current is produced
When a magnetic field is created by an induced current
It always acts against the chnage that made it
Electromagnetic induction is used to generate current in
alternators and dynamos
Alternators produce
a.c.
Dynamos produce
d.c.
How do dynamos work
The coil is rotated by a force, and it cuts through the magnetic fields
This induces a current, which changes direction every half-turn
A split-ring commutator is used to swap the connection every half turn and keep the current flowing the same direction
How do alternators work
The coil is rotated, so it cuts through the magnetic fields
A current is induced which changes direction every half-turn
Instead of using a split-ring commutator like dynamos, it has slip rings which means that the contact doesnt change every half-turn
This makes it produce a.c.
How do microphones use electromagnetic induction to work
Sound waves hit a flexible diaphragm that is attached to a coil of wire. The coil is wrapped around one pole of a permanent magnet, and another pole surrounds it.
As the diaphragm and coil moves, a current is induced in the coil
The amount of current generated depends on the properties of the sound, which allows the microphone to convert the sound waves to a current.
how do loudspeakers and headphones use electromagnetic induction to work
Opposite of microphone
The coil is wrapped around a magnetic pole and surrounded with the other pole
When the a.c flows through, a force is exerted on the coil
Thsi causes it to move the cone attached
The cone vibrates and causes sound waves to be produced
What do transformers do
Use induction to change the size of the potential difference of an alternating current
How do transformers work
There are two coils of wire wrapped around an iron core on each side
An alternating p.d. is applied across the primary coil, and it produces an alternatign magnetic field becuase iron is a magnetic material
The changing magnetic field induces an alternating p.d. across the secondary coil
Step-up transformers are
Transformers that increase the voltage. They have more coils in the secondary coil
Step-down transformers are
Transformers that decrease voltage. They have more coils in the primary coil
p.d. in primary coil / p.d. in secondary coil =
Turns in primary coil / turns in secondary coil
Why is electricity in the national grid at a high voltage
Either current or voltage needs to be high, due to the high power flowing through.
High current causes the wire to heat up, which loses energy. This means that step-up transformers are used to make it high voltage instead
Step-down transformers are used in the national grid to
Make the electricity usable and safe for domestic use
Transformers efficiency
100% efficient
In transformers:
Primary coil voltage x Primary coil current =
Secondary coil votage x secondary coil current
