Electrodynamics Flashcards
Faraday’s law
The emf induced is directly proportional to the rate of change of magnetic flux (flux linkage).
AC
Alternating current. Current which reverses direction periodically.
Commutator
A device which ensures that the direction of the current in a coil is reversed every half revolution.
Conventional current
The rate of flow of positive charge from the positive terminal of the cell to the negative terminal.
DC
Direct current. Current flowing in one direction only.
Electromagnetic induction
Occurs when a current is induced in a closed conducting loop when there is a change in the magnetic flux passing through the surface area of the conducting loop.
Induced emf
The total amount of electrical energy supplied per unit positive charge.
Magnetic fields
Produced by magnets or by moving electrical charges. Magnetic field lines are drawn to represent the direction of the magnetic field at a point. The symbol for magnetic field is B and its unit is the Tesla (T).
Magnetic flux density
A representation of the magnitude and direction of the magnetic field.
Magnetic flux
The product of the magnetic field (B) and the cross-sectional area (A) that the field lines pass through in an enclosed loop:Φ = BAcosθ
Magnetic flux linkage
The product of the number of turns on a coil and the flux through a coil (NФ).
Lenz’s law
The induced current flows in a direction so as to set up a magnetic field to oppose the change in magnetic flux.
Diode
A component that only allows current to flow in one direction.
Generator
A device which converts mechanical energy into electrical energy.
Motor
A device which converts electrical energy into mechanical energy.
What is the purpose of a split-ring commutator
To keep the torque on a DC motor from reversing every time the coil moves through the plane perpendicular to the magnetic field, a split-ring device called a commutator is used to reverse the current at that point.
What do motors do?
Convert electrical energy into mechanical energy.
What does a generator?
Convert mechanical energy into electrical energy
Function of a diode
The most common function of a diode is to allow an electric current to pass in one direction (called the diode’s forward direction), while blocking it in the opposite direction (the reverse direction).
Factors which affect the power of motor
Increasing the strength of the magnetic field
Increasing the strength of the current through the coils
Increasing the number of windings in the coils
Wrapping the coil around an iron ore
Using several coils wound at slightly different angles on the armature.
How to increase induced emf of AC generator
Increase magnetic field strength
Increase enclosed surface area of conducting loop
Used curved magnets (Keep coil moving perpendicular)
Rotate coil/loop at a faster rate
Increase number of windings
How does a transformer work?
Alternating current is sent to the primary coil by applying an AC voltage across the primary
coil.
This alternating current will cause a change in the magnetic field around the conductor
wound around the primary coil.
The change in magnetic field aroung the primary coil will cause a change in the magnetic flux
experienced by the secondary coil.
According to Lenz’s Law: The induced emf in the secondary coil will be of such a nature as to
induce a current within the secondary coil that forms a magnetic field to oppose the change
experienced in magnetic flux.
The input power and the output power will ALWAYS be equal in magnitude.
Advantage of AC
AC voltages can be stepped up or down using transformers.
AC voltages can be stepped up and electrical power can be transmitted over long distances
in power lines at low current to minimize the power loss due to heating.
It is easier and cheaper to convert AC to DC.
AC motors can produce a higher power output than DC motors.
