Topic 7 Flashcards
What are the 3 ways to change the size of an induced potential difference?
- Change the strength of the magnets.
- Move the wire more quickly.
- Increase the number of turns by making the wire a coil.
Which way do we draw lines on a magnet
North to south
Where is the magnetic field strongest on a magnet
At the poles
What are the two types of magnet
Permanent - always has own mag field
Induced - only is a magnet when placed in a mag field
What is a solenoid
When wire is coiled in order to increase the strength of the magnet
What is a solenoid with a iron core called
An electromagnet (field can be turned on and off with electric current)
What are electromagnets used for
Loud speakers
What are electromagnets used for
Loud speakers
What is the motor effect
A wire carrying a current creates a magnetic field. This can interact with another magnetic field causing a force that pushes the wire at right angles
What does a split ring commutator do
Swaps contacts every half turn which keeps the motor rotating in the right direction
What is the generator effect
The induction of a potential difference in a wire which is experiencing a change in magnetic field
What type of current do alternators generate
What type do dynamos generate
Alternators - alternating
Dynamos - direct
What do slip ring commutators do
Makes connection between rotating and stationary conductors
How can we see the generated pd in a coil
Use an oscilloscope
How do loud speakers work
Send ac through a coil which surrounds a permanent magnet.
This is surrounded by the other pole which causes a force on the coil. (This causes the cone to move)
When the ac current reverses the force acts in the opposite way and causes the cone to move
The variations in current make the cone vibrate which makes the air pressure change and produce a sound wave.
This sound wave is the same frequency as the frequency of the ac
How do microphones work
Sound waves hit a flexible diaphragm - this is attached to a coil wrapped around a magnet
This causes the coil to move in the magnetic field which generates current
The movement of the coil depends of sound wave (bigger moves more)
This is how microphones convert pressure variations of a sound wave into variations in electric current
What does a transformer do
Changes pd of an alternating current.
How does a transformer work
2 coils of wire joined with an iron core . ac is applied to the primary coil. The iron core magnetises and demagnetises quickly causing a pd in the second coil.
If the second coil is in a complete circuit current is induced.
Step up vs step down transformer could
Step up - more coils on secondary
Step down - more coils on primary
