P7 - Magnetism and Electromagnetism Flashcards
What do all magnets produce?
A magnetic field
A magnetic field is a region where other magnets or magnetic materials experience a non-contact force.
What are the two poles of a magnet?
- North (or north seeking)
- South (or south seeking)
All magnets have these two poles.
What direction do magnetic field lines go?
From north to south
They show the direction of the force experienced by a north pole.
What does it mean if magnetic field lines are closer together?
The magnetic field is stronger
The strength of the magnetic field decreases with distance from the magnet.
Where is the magnetic field strongest?
At the poles of a magnet
A north pole will feel a force towards the stronger magnetic field.
What happens when like poles of magnets are near each other?
They repel each other
Unlike poles attract each other.
What is inside a compass?
A tiny bar magnet
The north pole of this magnet is attracted to the south pole of any nearby magnet.
What direction do compasses point when not near a magnet?
North
This is due to the Earth’s own magnetic field.
What are the two types of magnets?
- Permanent magnets
- Induced magnets
Permanent magnets produce their own magnetic field, while induced magnets become magnets when in a magnetic field.
What happens to induced magnets when the magnetic field is removed?
They quickly lose their magnetism
Induced magnets stop producing a magnetic field when the external magnetic field is removed.
True or False: The force between permanent and induced magnets is always attractive.
True
This applies to the interaction between permanent magnets and induced magnets.
What is created around a wire when a current flows through it?
A magnetic field
The magnetic field consists of concentric circles perpendicular to the wire, with the wire at the center.
What happens to the direction of the magnetic field when the direction of the current changes?
It changes direction
The right-hand thumb rule can be used to determine the new direction of the magnetic field.
Describe the right-hand thumb rule.
Point your thumb in the direction of current and curl your fingers
The direction of your fingers indicates the direction of the magnetic field.
What is a solenoid?
A coil of wire
Wrapping the wire into a coil increases the strength of the magnetic field produced.
What happens to the field lines around each loop of wire in a solenoid?
They line up with each other
This alignment results in many field lines pointing in the same direction, increasing the field strength.
How is the magnetic field inside a solenoid described?
Strong and uniform
It has the same strength and direction at every point within that region.
What do the ends of a solenoid act like?
The north pole and south pole of a bar magnet
The right-hand rule can be used to determine which end is which.
What happens to the magnetic field when you stop the current in a solenoid?
The magnetic field disappears
A solenoid with an iron core can act as an electromagnet, with the magnetic field being turned on and off with electric current.
What is an electromagnet?
A solenoid with an iron core
It is a magnet whose magnetic field can be turned on and off with an electric current.
What is the motor effect?
The motor effect occurs when a current-carrying wire is placed in a magnetic field.
At what angle must a wire be to experience the full force in a magnetic field?
90° to the magnetic field.
What happens if the wire runs parallel to the magnetic field?
It won’t experience any force at all.
What three factors does the force acting on a conductor in a magnetic field depend on?
- Magnetic flux density
- Size of the current
- Length of the conductor in the magnetic field
What is the unit for magnetic flux density?
Tesla (T)
What does Fleming’s left-hand rule help to determine?
The direction of the force on a current-carrying conductor in a magnetic field
Fleming’s left-hand rule utilizes the thumb, first finger, and second finger to indicate force, magnetic field, and current direction respectively.
How do you apply Fleming’s left-hand rule?
1) Point your first finger in the direction of the magnetic field.
2) Point your second finger in the direction of the current.
3) Your thumb will point in the direction of the force (motion)
If either the current or the magnetic field is reversed, the direction of the force will also be reversed.
What does the split-ring commutator do in a motor?
Swaps the contacts every half turn
This mechanism keeps the motor rotating in the same direction.
How can the direction of the motor be reversed?
1) Swapping the polarity of the DC supply (reversing the current)
2) Swapping the magnetic poles (reversing the field)
Both methods change the interaction between the current and magnetic field.
What are three ways to increase the speed of a motor?
1) Increasing the current
2) Adding more turns to the coil
3) Increasing the magnetic flux density
These factors enhance the force acting on the coil, thus increasing its speed.
True or False: The coil can turn both clockwise and anticlockwise.
True
The direction of rotation depends on the current and magnetic field orientation.
What is the relationship between the current and the motion of the coil?
The direction of the current affects the direction of the motion
Reversing the current will reverse the motion direction as indicated by Fleming’s left-hand rule.
