Magnetism and Electromagnetism Flashcards
What is a magnetic field?
The region around a magnet, where a force acts on another magnet or magnetic material.
What are permanent magnets?
Magnets which produce their own magnetic field.
What are induced magnets?
Magnets which become magnetised when placed in a magnetic field.
In what direction do arrows on field liners always run?
From north to south.
What is flux density?
The density of the field lines, which indicates the strength of the field at that point (the more concentrated the liners; the stronger the field).
What can a compass show?
The fact that the needle aligns with the Earth’s magnetic field, proves that Earth’s core must be magnetic.
What happens when a current flows in a conducting wire?
A magnetic field is produced around the wire.
What does the right hand grip method show?
The direction of the field lines depending on the direction of current.
How does the right hand grip method work?
The way the fingers point represent the direction of the magnetic field.
The direction the thumb is pointing represents the direction of current.
What does the strength of a magnetic field depend on?
The size of the current and the distance from the wire.
When is a solenoid formed?
When wire is looped into a cylindrical coil.
How does a solenoid increase the strength of the magnetic field?
It creates a strong, uniform field inside the solenoid.
It concentrates a longer piece of wire into a smaller area.
The looped shape means that the magnetic field lines around the wire are all in the same direction.
How can one increase the field strength?
By making a solenoid.
By giving it an iron core.
Describe how an electric bell works.
The electromagnet is magnetised, which attracts armature.
The hammer strikes the gong and breaks the circuit.
The armature springs back, completing the circuit again and demagnetising the electromagnet.
What is the motor effect?
When a current carrying conductor is placed in a magnetic field and it experiences a force.
What causes the motor effect?
The field created by the current interacting with the magnetic field.
How might the force if a magnetic field be increased?
By increasing the size of the current, the length of conductor, the flux density.
What happens if the direction of the current or the direction of the magnetic field is reversed?
The direction of the force will reverse.
What does Fleming’s left hand rule find?
The direction of the force on the conductor.
What position is Fleming’s left hand rule?
When the thumb, first and second finger on the left hand are all at right-angles.
In Fleming’s left hand rule, what does the first finger represent?
The direction of the magnetic field, from north to south.
With a rotation of the wrist to re-align the second finger, where should it now point?
Along the wire in the direction the current is flowing.
In Fleming’s left hand rule, where should the thumb finally be pointing?
The direction of force.
Why will a current carrying coil in a magnetic field rotate?
The current going up one side of the coil is in the opposite direction to the current coming back down the other side, so one side moves up and the other side moves down.
In electric motors, what does the brush contacts at the commutator do?
It ensures that the current direction in the coil is always the same direction.
This makes sure that the motor keeps rotating and does not stop.
What will make an electric motor run faster?
Increasing the current or magnetic field.
How could one make an electric motor rotate in another direction?
By reversing the current of the magnetic field.
In motors, what is the motor effect used to do?
Convert electrical emery into kinetic energy.
