P17 Magnets and electromagnets Flashcards
When will poles of a magnet repel?
When they are the same pole
e.g N and N
When will the poles of a magnet attract?
When the poles are different
e.g N and S
In which direction to field lines always go?
From North towards South
What is a permanent magnet?
It produces its own magnetic field which is always there
What is an induced magnet?
An object that becomes magnetic when it is placed in a magnetic field
What can be used to plot the magnetic field around a magnet?
A compass
How can you increase field strength of an electromagnet?
Increase current
Increasing the number of turns of the coil
Adding an iron core.
What is a solenoid?
A cylindrical coil of wire
What is the shape of the magnetic field around a solenoid?
Same as the field lines of a bar magnet
How can you increase the magnetic field of a solenoid?
Iron core
More turns around the wire
Advantages of electromagnets
Can be turned on and off
Strength of magnet can be adjusted
What is a magnetic field?
The region of space around a magnet where a magnetic material will experience a force.
What does the distance between magnetic field lines indicate?
Strength of the field
Closer together = Stronger field
What is produced around a wire when an electric current flows through it?
A magnetic field
What does Fleming’s left hand rule show?
Relative orientation of the force, current and magnetic field for the motor effect.
What is the the motor effect?
When a conductor placed in a magnetic field experiences a force.
What causes the motor effect?
A wire carrying a current creates a magnetic field.
This can interact with another magnetic field, causing a force that pushes the wire at right angles
Examples of the motor effect
Headphones
Loudspeakers
Why does the motor spin in the motor effect?
Each side of the coil experiences a force.
The forces in each side of the coil are in opposite directions.
What keeps the motor spinning in the same direction? (Motor effect)
Split ring commutator
The end of the wire swaps contact with the power supply every half turn, so the current always flows in the same direction.
How can a motor be made to spin faster?
Increasing current
Increasing strength of magnetic field
How can a motor be made to spin in the opposite direction?
Reversing the direction of the current
Reversing the direction of the magnetic field
What do headphones and loudspeakers do? (Motor effect)
They convert variations in current in electrical circuits to pressure variations in sound waves.
