Topic 12 - Magnetism And The Motor Effect Flashcards
What is an electromagnet?
- A solenoid with an added iron core
- Adding the iron core increases the strength of the magnetic field
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
First finger Flemings LH Rule:
Magnetic field
Second Finger Flemings LH Rule
Current Flow
Thumb Flemings LH Rule
Direction of the force
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?
- Direction of the force is reversed
If the strength of the current in a current carrying wire placed in a uniform magnetic field is increased, what happens to the force?
The strength of the force is increased.
Equation linking force, magnetic flux density, current and length.
Force (N) = Magnetic Flux Density (T) x Current (A) x Length (m)
F = BIL
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
If the current and magnetic field are parallel to each other, which direction would the force act in?
No force will act
How does an electric motor work?
- A coil of wire, carrying a current, 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.
At which part of a magnet are the magnetic forces strongest?
The poles
What happens when two magnets are brought close to each other?
They exert a force on each other
What type of force is exerted if two like poles of a magnet are brought near each other?
- A repulsive, non-contact force.
What type of force is exerted if two unlike poles of a magnet are brought near each other?
An attractive, non-contact force.
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?
- Permanent magnet produces its own magnetic field.
- Induced magnet becomes magnetic when placed in a magnetic field
Induced magnetism always causes what type of force?
Force of attraction.
What is the effect when an induced magnet is removed from a magnetic field?
The induced magnet loses most/all of its magnetism.
Four examples of magnetic materials:
- Iron
- Steel
- Cobalt
- Nickel
What can always be said about the force between a magnet and a magnetic material?
It is always attractive
How does the strength of a magnetic field alter as you move further away from the magnet producing it?
The magnetic field strength decreases the further you move away,
In what direction does a magnetic field point?
- In the direction of the force that a North Pole would experience if placed in the field.
- From the north seeking pole to the south seeking pole of a magnet.
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-carrying wire?
The magnitude of the current flowing through the wire.
Does a high concentration of field lines mean the field is strong or weak?
Strong
Do magnetic field lines ever cross each other?
No, they never cross, touch or overlap
How is a plotting compass used to map out a magnetic field?
- Place a compass (with a needle magnet) on a piece of paper near the field.
- Draw an arrow in the direction the compass points.
- Repeat at different points on the paper.
- Join the arrows to make a complete field pattern.
What is a solenoid?
- A coil of wire which when current passes through creates a strong magnetic field
Describe the magnetic field found inside a solenoid
Strong and uniform
If the field on the outside of a solenoid strong or weak? Why?
- Weak
- This is because the fields from each coil cancel out, making the outside field weak.
