Topic 07: Electric and Magnetic Fields Flashcards
Capacitance
The ratio of the charge stored in a capacitor to the potential difference between the two sides of the capacitor
Coulomb’s law
The size of the force that acts between two point charges is proportional to the product of their charges and inversely proportional to the square of their separation. It is attractive for opposite charges and repulsive for like charges
Dielectric
An insulating material placed between capacitor plates that prevents charge from crossing between the plates. The dielectric becomes polarised when the capacitor is charged and changes the capacitance of the capacitor
Eddy current
Small closed loops of current within a conductor or magnet. In a transformer, these currents act against the magnetic flux that generates a current in the secondary coil, making the transformer less efficient and heating the core
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
Electric field lines
A way of representing an electric field in a diagram, they point in the direction that a positive charge would experience a force, point positive to negative
Electric field strength
Defined at a point. The electrostatic force experienced by a unit positive charge at that point in the field
Electric potential
Defined at a point. The work done moving a unit positive charge from an infinite distance away to that point
Electric potential difference
The work done moving a unit positive charge between two points
Electromagnetic induction
When a current carrying conductor moves relative to a magnetic field, an EMF is induced in the conductor
Electrostatic force
The force generated between charges due to Coulomb’s law
Equipotential
Planes of points where the electric potential is the same, no work is done moving charge along these lines
Faraday’s law
The magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linkage
Fleming’s left hand rule
The relative direction of motion, field direction, and current direction in the motor effect can be represented by the thumb, first finger, and second finger of the left hand respectively
Frequency
The number of complete oscillations of the current (or voltage) in an A.C. circuit per second
Lamination
When a transformer’s core is made up of sets of layers to prevent eddy currents
Lenz’s law
The direction of an induced current is such that it opposes the current that created it
Magnetic field
A region of space in which magnetic materials and moving electric charges feel a force
Magnetic flux
The magnetic field passing through a given area. Given by the product of the magnetic flux density and the area
Magnetic flux density
Magnetic flux linkage
The magnetic flux of a coil found by the product of the magnetic flux and number of turns of a coil
Motor effect
The force felt by a current carrying wire in a magnetic field
Oscilloscope
A device used to monitor periodically time-changing quantities, such as voltage or current, in an A.C. circuit
Peak value
The maximum voltage or current that an A.C. Current achieves
Period
The time taken for the current (or voltage) in an A.C. circuit to complete one full cycle
Radial field
A field with field lines originating from a point like spokes on a wheel
Root-mean-square value
For an A.C. circuit, RMs is the value of the voltage or current that would produce the same power dissipation in a D.C. Circuit as the A.C. Circuit, It is defined as the peak voltage divided by square root 2
Time constant
Describes the rate of charge or discharge of a capacitor. It is the time taken for the capacitor to charge from zero to 63% of its full value or to discharge from full to 37% of its full value
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. The transformer is step-up if the number of coils on the secondary coil is greater than the number of turns on the primary coil. The transformer is step-down if the number of turns on the secondary coil is fewer than the number on the primary coil
Uniform field
A field with parallel field lines
