Flashcards in Deck 7 = Electromagnetism Deck (26):
What does a simple electromagnet consist of?
A simple electromagnet can be switched on and off and consists of coil, with several hundred turns in an insulated copper wire. When a current is put through the wire a magnetic field is created.
The strength of the magnetic field is increased by?
- Increasing the current.
- Increasing the number of turns in the coil.
Revering the current?
Reverses the direction of the magnetic field.
What is the magnetic relay?
The switch operated by an electromagnet. It is used mainly in a electronic buzzer, alarm or door bell. Full information is available on page 218.
What is a circuit breaker?
The circuit breaker is an automatic switch which cuts off the current in a circuit if this rises above a specified value. It has the same effect as a fuse, however it is unlike a fuse because it can be reset (it can trip).
How does the electric bell work?
The electric bell contains an electromagnet that continuously switches itself off and on quickly, moving the hammer as it does. The arrangement is called the make and break circuit because of the fact that as the hammer hits the bell the circuit is disconnected.
What is the purpose of the core?
The core is needed to magnify the magnetic field to thousands of times the strength of the field of just the coil alone. The core also makes it easier to wrap the copper wire.
Fact of the Universe (The motor effect)?
A CURRENT carrying wire in a magnetic field will experience a force.
We can predict the motor effect using......?
Flemming's left hand law.
The thumb points in direction of?
The first finger points in direction of?
The second finger points in direction of?
Direction of Current (positive to negative)
Briefly describe the turning effect on a coil?
The coil lies between two magnets. The current flows in opposite directions along the two sides of the coils. So according to Flemming's left hand rule, one side is pushed up and the other down. Therefore a turning effect is created on the coil. With more turns in the coil, the turning effect increases.
In a motor how is the current reversed to the motor will make a full rotation?
The direction of current must be reversed every half a turn, otherwise the coil comes to a halt. This is achieved using a conducting ring spit in two, called a split ring or communicator. A coil wire is used with lots of turns to increase the effect of the magnetic field.
How do you cause a load speaker to work?
The cylindrical magnet produces a strong radial magnetic field at right angles to the wire in the coil. The coil is free to move backwards and forwards and is attached to a stiff paper cone.
How does a load speaker create sound?
The loudspeaker is connected to an amplifier which gives out alternating current. This flows backwards, forwards, backwards...and so on, causing an effect on the coil which is also backwards, forwards, backwards... As a result, the cone vibrates and gives out sound waves. The sound you hear depends on how the amplifier makes the current alternate.
Faraday's law of electromagnetic induction?
The EMF induced in a conductor is proportional to the rate at which magnetic field lines are cut by the conductor.
What is electromagnetic induction?
When a wire is moved across a magnetic field, a small EMF (voltage) is generated in the wire.
The induced EMF (and current) can be increased by?
- Moving the wire faster.
- Using a stronger magnet.
- Increasing the length of wire in the magnetic field - for example, by looping the wire through the field several times.
Either the following will reverse the direction of the induced EMF and current?
- Moving the wire in the opposite direction
- Turning the magnet round so that the field direction is reversed.
If the wire is not moving, or is moving in parallel to the filed lines...?
There is no induced EMF or current.
The induced EMF is...?
Voltage is measured in?
Ways of induced EMF?
Look in text book Page 225. The shake-able torch etc.
When the switch is closed the coil spins on the axle, state why? (2)
Electrical current is passed through the coil in a magnetic field.