Chapter 15 - electromagnetic machines Flashcards
What is a magnetic field?
A region where a force is exerted on a magnetic material
How can magnetic fields be represented?
field lines?
In which direction do field lines travel?
North to South
How is the strength of a magnetic field represented by field lines?
The stronger a field is, the closer together the field lines will be
What is a neutral point?
A point at which the magnetic fields cancel out
What will be generated around a wire carrying an electric current?
A magnetic field
What is the right hand grip rule used for?
Finding the direction of a magnetic field around a current carrying wire
What is the right hand grip rule?
Direction of thumb = current
Curl of fingers = magnetic field
What is a solenoid?
A form of electromagnet - coil/multiple coils of wire which act like a bar magnet when carrying a current
What happens when a current carrying wire is in an external magnetic field?
The wire experiences a force
(because the magnetic fields around the wire and the external magnetic field interact, so the field lines around the magnet contract)
What happens when a current carrying wire is in an external magnetic field, but the current is parallel to the magnetic field lines?
No force will act
When a wire is in an external magnetic field, in what direction will the force on the wire be?
perpendicular to both the magnetic field and the current direction
What is Fleming’s left hand rule used for?
Finding the direction of force on a current carrying wire in a magnetic field
What is Fleming’s left hand rule?
thumb = force
first finger = field
second finger = current
What is the equation for finding the size of the force on a current carrying wire in an external magnetic field?
F = BIL force = magnetic field strength x current x length of wire
What is the symbol for magnetic field strength?
B
What is the definition of magnetic field strength?
The force on one metre of wire, carrying a current of one amp at right angles to the magnetic field
What is another name for magnetic field strength?
Magnetic flux density
What is magnetic field strength/magnetic flux density measured in?
Teslas, T
What are the equivalent units to one Tesla?
Wbm^-2
Webers per metre squared
What is magnetic flux density?
The number of flux lines per unit area
the magnetic field strength
Is magnetic field strength a vector or scalar quantity?
vector
How does a motor work?
A current carrying loop is placed in an external magnetic field, which causes it to rotate
A split ring commutator reverses the current every half turn to keep the motor spinning in a constant direction
What does a split ring commutator do?
Reverses the current in a motor’s loop with every half turn, to keep it spinning in a constant direction
How does an induction motor work?
The magnetic field is altered around a coil of wire which is free to move, inducing a current and causing the wire to rotate
What is the magnetic flux density?
The magnetic field strength per unit area
What is the equation for finding the magnetic flux?
Φ = BA
magnetic flux = magnetic field strength x area