Unit 4 - Lesson 8: Simple D.C. Motors & Loudspeakers Flashcards
How do loudspeakers work?
Loudspeakers make use of the motor effect.
A wire is coiled around a permanent magnet in the base of a speaker (beneath the cone).
Alternating electric currents from a radio (for example) pass through the coils. These changes in magnitude and direction represent the sound to be produced.
Because the current is alternating, the magnetic fields are constantly changing strength and direction (according to Flemings left hand rule).
These movements make the cone vibrate (move in different directions because the alternating current is moving in different directions) which in turn creates sound.
Draw a diagram of the inside of the speaker base: a permanent magnet wrapped in wire.
https://i.pinimg.com/736x/4b/1d/c7/4b1dc779fa6f28b4cd583b606cb272d7.jpg
How does a simple DC motor work?
A current-carrying loop of wire is placed between two permanent magnets.
The wire produces a magnetic field and the permanent magnets produce a magnetic field.
This causes the loop to rotate due to the force acting in opposite directions on each side of the coil.
We can show this using Fleming’s left-hand rule. The current on the left-hand side of the wire will be moving in the opposite direction to the current on the right hand side. As the field is the same, this will cause the one side to move up and the other down.
Traditionally, we say that this will turn the coil clockwise..
If we had no way of changing the direction of the current, after the coil had rotated through 90 degrees, the force would start acting against the direction of rotation.
A split ring commutator allows us to switch the current direction every half cycle, allowing us to maintain the direction of rotation.
There are three ways the simple DC motor can be sped up. What are they?
- Increasing the current.
- Coiling the wire more.
- Increasing the strength of the magnetic field.
Draw a diagram to show how the DC motor is turned.
Use RED to represent the electric current.
Use PURPLE or BLUE to represent the magnetic field.
Use GREEN to represent the magnetic force.
Use BLACK to represent a torque.
https://i.pinimg.com/736x/7f/f0/bc/7ff0bcf581037fdff37c27fec5bfc556.jpg
Explain how increasing the current will speed up the simple DC motor.
When electric current passes through a coil in a magnetic field, the magnetic force produces a torque, which turns the DC motor.
What does a commutator allow us to do?
An electric current can be supplied externally through a commutator, allowing us to switch the current direction every half cycle (in a simple DC motor) and allowing us to maintain the direction of rotation.
