Topic 12 - Magnetism And The Motor Effect Flashcards
At which part of a magnet are the magnetic forces strongest?
The poles
What type of force is exerted if two like poles of a magnet are brought near each other?
They repel each other
What type of force is exerted if two unlike poles of a magnet are brought near each other?
They attract each other
What is a magnetic field?
The region surrounding a magnet where another magnet or magnetic material experiences a non-contact force
What is the difference between a permanent magnet and an induced magnet?
A permanent magnet produces its own magnetic field
An indices becomes magnetic when placed in a magnetic field
What type of force is always caused by induced magnetism?
Attraction
Give four examples of magnetic materials?
Iron, steel, cobalt, nickel
How does the strength of a magnetic field as you move further away from the magnet?
The strength decreases
In what direction does a magnetic field point?
From the North Pole to the south
What does a magnetic compass contain?
A small bar magnet that points in the direction of the Earth’s magnetic field
What is produced when current flows through a conducting wire?
A magnetic field is produced around the wire
What determines the strength of the magnetic field around a current-varying wire?
The magnitude of the current flowing through the wire
What does a high concentration of field lines mean?
The field is strong
How is a plotting compass used to map out a magnetic field?
Place the compass of a piece of paper, draw an arrow in the direction the compass points. Repeat at different points on the paper. Join the arrows and make a complete field pattern
What is a solenoid?
A could of wire which creates a strong magnetic field when current passes through it.
Describe the magnetic field inside a solenoid
Strong and uniform
Is the field on the outside of a solenoid strong or weak? Why?
Weak because the fields from each coil cancel out, making the outside field weak
What is an electromagnet?
A solenoid with an added iron core.
What is the motor effect?
When a force is exerted between a magnetic field and a current-carrying conductor placed in that field
What rule is used to determine the force produced by the motor effect?
Fleming’s left-hand rule
What do each of the fingers represent in fleming’s left hand rule?
The forefinger = magnetic field
Second finger = current flow
Thumb = direction of force produced by motor effect
What factors affect the size of the force on a current-carrying wire in a magnetic field?
The magnitude of the current flowing through the conductor
The strength of the magnetic field that the conductor is placed in
If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force?
The direction of the force is reversed
If the strength of the current in a current-carrying wire placed in a a uniform magnetic field is increased, what happens to the force?
The strength of the force is increased
How do you calculate force? (magnetic flux)
Force = magnetic flux density x current x length
What criteria must be met for the equation linking force, magnetic flux density , current and length to hold?
The conductor must be at right angles to the magnetic field it is placed in
What unit is used for magnetic flux density?
Tesla
If the current and the magnetic field are parallel to each other, which direction would the force act in?
No force will act
How does al electric motor work?
A coil of wire is placed in a magnetic field
The forces on the two sides perpendicular to the field experience forces in opposite directions. This causes a rotational effect
How are electric motors kept rotating?
A split ring commutator is used. This switches the current direction every half turn, which ensures that the coil keeps spinning
