Electric and Magnetic Fields Flashcards
What is capacitance?
The ratio of the charge stored in a capacitor to the potential difference between the two sides of the capacitor.
What does Coulomb’s Law describe?
The size of the force acting between two point charges is proportional to the product of their charges and inversely proportional to the square of their separation.
What is a dielectric?
An insulating material placed between capacitor plates that prevents charge from crossing between the plates.
True or False: The dielectric becomes polarised when the capacitor is charged.
True
What are eddy currents?
Small closed loops of current within a conductor or magnet.
How do eddy currents affect a transformer?
They act against the magnetic flux that generates a current in the secondary coil, making the transformer less efficient and heating the core.
Define electric field.
A region of space in which charged particles experience either an attractive or repulsive force depending on the charge of the particle and direction of the field.
What do electric field lines represent?
They point in the direction that a positive charge would experience a force, pointing from positive to negative.
What is electric field strength?
Defined at a point as the force experienced by a unit positive charge at that point in the field.
What is electric potential?
The work done moving a unit positive charge from an infinite distance away to that point.
Electric potential difference is defined between _______.
two points.
What is electromagnetic induction?
When a current carrying conductor moves relative to a magnetic field, an EMF is induced in the conductor.
What is electrostatic force?
The force generated between charges due to Coulomb’s Law.
What are equipotential planes?
Planes of points where the electric potential is the same, no work is done moving charge along these lines.
What does Faraday’s Law state?
The magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linkage.
What does Fleming’s Left Hand Rule represent?
The relative direction of motion, field direction, and current direction in the motor effect using the thumb, first finger, and second finger of the left hand.
What is frequency in the context of an A.C circuit?
The number of complete oscillations of the current (or voltage) per second.
What is lamination in transformers?
When a transformer’s core is made up of sets of layers to prevent eddy currents.
What does Lenz’s Law state?
The direction of an induced current is such that it opposes the current that created it.
Define magnetic field.
A region of space in which magnetic materials and moving electric charges feel a force.
What is magnetic flux?
The magnetic field passing through a given area, given by the product of the magnetic flux density and the area, measured in Weber
What is magnetic flux density measured in?
Tesla.
What is magnetic flux linkage?
The magnetic flux of a coil found by the product of the magnetic flux and the number of turns of a coil.
What is the motor effect?
The force felt by a current carrying wire in a magnetic field.
What is an oscilloscope used for?
To monitor periodically time changing quantities such as voltage or current in an A.C circuit.
What is the peak value in an A.C circuit?
The maximum voltage or current that an A.C circuit achieves.
What is the period in an A.C circuit?
The time taken for the current (or voltage) in an A.C circuit to complete one full cycle.
Define radial field.
A field with field lines originating from a point like spokes on a wheel.
What is the Root-Mean-Square (RMS) Value in an A.C circuit?
The value of the voltage or current that would produce the same power dissipation in a D.C circuit as the A.C circuit, defined as the peak voltage divided by square root 2.
What does the time constant describe?
The rate of charge or discharge of a capacitor.
What is a transformer?
A device used to increase or decrease the voltage with two sets of coils with different numbers of turns wrapped around a magnetic core.
What is a step-up transformer?
A transformer where the number of coils on the secondary coil is greater than the number on the primary coil.
What is a step-down transformer?
A transformer where the number of coils on the secondary coil is fewer than the number on the primary coil.
Define uniform field.
A field with parallel field lines that are evenly spaced.
1Volt =
1 Joule per coulomb
What is the time constant of a capacitor circuit?
RC, measured in seconds and is the time it takes for the current/voltage to drop to 37%.
How many RC’s must pass before a capacitor is said to be completely discharged or charged?
5RC’s
Magnetic fields lines must never cross.
true or false?
True
What is a neutral point in a magnetic field?
a point where the magnetic fields cancel out
