P4.2 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 experienced due to the motor effect?
flemings left hand rule
when using flemings left hand rule what does the second finger represent
the second finger points in the direction of current flow in the conductor
when using flemings left hand rule what does the forefinger represent
the forefinger points in the direction of the magnetic field
when using flemings left hand rule what does the thumb represent
the thumb points in the direction of the force produced, and therefore the motion produced by 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
the direction of the force is reversed
if the strength of the current in a current-carrying wire placed in a uniform magnetic filed is increased what happens to the force
the strength of the force is increased
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
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
what equation is used to calculate the force that a current carrying wire experiences in a field?
force (N) = magnetic flux density (T) x current (A) x length (m)
F = BIL
what is the unit used for magnetic flux density
tesla, T
explain how a loudspeaker works
a cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field.
when current flows through the wire, it creates a second magnetic field, which interacts with the permanent field.
this produces a force which causes the cone to vibrate
how do loudspeakers make use of the motor effect
the motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound
how is the pitch of the sound from a loudspeaker changed?
the frequency of the a.c current is altered
this creates a different frequency of vibration in the cone
what happens when an electrical conductor moves relative to a magnetic field?
a potential difference is induced across the ends of the conductor
what happens to an electrical conductor when there is a change to the magnetic field that it is placed in
a potential difference is induced across the ends of the conductor
what is the requirement for an induced potential difference to cause a current flow?
the conductor must form a closed loop or be part of a complete circuit
if there is a change in the magnetic field around a conductor, explain what changes occur in the conductor
a potential difference is induced across its ends.
this drives a current
the direction of the induced current is such that it creates a magnetic field that opposes the change in the existing field.
what can be said about the direction of the magnetic field produced by an induced current
the direction of the field is such that is opposes the change that induced the current
this change is either the movement of the conductor or a change to the field.
what electromagnetic effect does a microphone take advantage of and how
the generator effect.
it converts the pressure variations in sound waves into alternating current in a circuit
what are two ways that the generator effect is used to generate different types of current
in an alternator to produce alternating-current
in a dynamo to produce direct-current.
describe the makeup of a basic transformer
a primary coil and a secondary coil of wire wrapped around an iron core.
