P15 - Electromagnetism Flashcards
What are the two poles of a magnet?
North and South
Where on a magnet is the magnetic force the strongest?
At the poles
What are the two types of magnet?
Give an example of each.
Permanent and Induced
Permanent: Bar Magnet
Induced: Iron, Nickel, Cobalt
What is a solenoid?
A coil of insulated wire, which produces a magnetic field when a current passes through it.
How can you increase the strength of an electromagnet?
Use an Iron Core
Increase the number of coils
What is the direction of the Conventional Current?
Positive to Negative
Why are metals such as Iron an induced magnet?
They can be magnetised when placed in a magnetic field.
They contain magnetic domains which are organised randomly throughout the metal.
When the object is placed in a magnetic field, the magnetic domains align themselves with the magnetic field, creating its own magnetic field and therefore becoming magnetised.
The region around a magnet is called what?
A magnetic field
How do you reverse the direction of the magnetic field in a solenoid?
Reverse the current
What rule can be used to determine the direction of the magnetic field, current, or motion?
Flemming’s Left Hand Rule
What is the equation that links:
Force, Magnetic Flux Density, Current, and Length? State the units
Force (F) = Magnetic Flux Density (B) × Current (I) × Length of wire (L)
F = BIL
F - N (Newtons)
B - T (Tesla)
I - A (Amps)
L - M (Metres)
What direction do magnetic field lines go?
North to South
What is a uniform magnetic field?
All the field lines are parallel to the axis of the solenoid and are all in the same direction
How does an electromagnet work?
A coil of wire is wrapped around an iron core.
When the current passes through the wire, it becomes a solenoid.
The solenoid produces its own magnetic field.
The iron core, now inside a magnetic field, becomes magnetised (an induced magnet).
This becomes the magnetic field of the electromagnet much stronger as it now consists of the Mag. Field of the solenoid AND the iron core.
The electromagnet is then able to act as a regular magnet.
When the current is removed, the magnetism is lost quickly.
What rule can be used to determine the direction of the magnetic field?
Right hand grip rule
What is a circuit breaker?
A switch in series with an electromagnet.
The switch is held closed by a spring.
When the current is too large, the switch is pulled open by the electromagnet.
The switch stays open until it resets manually.
How does an electric bell work?
Electric bell is connected to a battery
Iron armature is pulled on to the electromagnet
Make-and-break switch is therefore opened
Electromagnet is switched off
Armature springs back
Make-and-break switch closes again
Cycle repeats.
How does a relay work?
The relay is used to switch an electrical machine on or off.
The electromagnet pulls the iron armature onto it.
This closes the switch gap.
This switches the machine on.
In this way, a small current is used to switch on a machine with a much bigger current.
What is the motor effect?
The force acting on a wire in a magnetic field when a current is passed through the wire.
The size of the force of the motor effect can be increased by?
Increasing the current
Using a stronger magnet
The size of the force of the motor effect depends on the angle.
When the wire is PERPENDICULAR to the magnetic field lines, the force is at its greatest
When the wire is PARALLEL to the magnetic field lines, the force is 0
You can control the speed of an electric motor by doing what?
Changing the current.
How can you reverse the direction the motor turns?
Reverse the current
When a current is passed through the coil in a motor, the coil spins, why?
A force acts on each side of the coil due to the motor effect
The force on one side is in the opposite direction to the force on the other side.
