Fields And Their Consequences Definitions Flashcards
Define back EMF
An emf generated by the coil in an AC generator that acts against the potential difference that has been supplied to the motor
Define capacitance, C
The charge stored per unit pd in a capacitor
Define capacitor
An electrical component that stores charge. A parallel-plate capacitor is made of two parallel conducting plates with an insulator between them (dielectric)
Define 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.
Define cyclotron
A particle accelerator made up of two D shaped electrodes positioned opposite each other. The electric field changes direction each time a particle moves from one electrode to the other, causing the particle to accelerate
Define dielectric
An insulating material placed between the two plates of a capacitor in order to increase the amount of charge it can store
Define electrical conductor
A material that contains free electrons that are able to move throughout the material and carry charge
Define electrical insulator
A material that does not contain any free electrons. All electrons in an insulator are part of the individual atoms that make it up.
Define electric field
A region surrounding a charged object which causes a force to be exerted on any charged object placed within the field
Define electric field strength ,E (at a point in the field)
The force per unit positive charge exerted on a charged object placed at that point in the field. This is a vector acting in the same direction as the force on a positive charge.
Define electric potential, V (at a point in the field)
The work done per unit charge in a positive test charge in bringing it from infinity to that point in the field.
Define electromagnetic induction
When an emf in induced in a wire/conducting rod when it is moved relative to a magnetic field.
Define equipotential
A surface of constant potential. No work is done by the field when an object moves along an equipotential
Define escape velocity
The minimum velocity required by an object to be able to escape a gravitational field of a mass when projected vertically from its surface.
Define Faraday’s law
The magnitude of the induced emf is equal to the rate of change of flux linkage through the circuit
Define field line/line of force
A line representing the path that a North Pole (magnetic field), positive charge (electric field) or mass (gravitational field) would take when placed within the field
Define force field
An area in which an object will experience a non-contact force
Define geostationary satellite
A satellite that orbits above the equator with a 24 hour period, so it will always remain above the same position on the Earth. They orbit approximately 36,000km above the surface of the Earth.
Define gravitational field
A regional surrounding a mass in which any other object with mass will experience an attractive force.
Define gravitational field strength
The force per unit mass exerted on a small test mass placed within the field
Define gravitational potential, V (at a point in the field)
The work done per unit mass required to move a small test mass from infinity to that point
Define gravitational potential energy
The component of an object’s energy due to its position in a gravitational field
Define Kepler’s third law
The square of an object’s orbital period (T) is directly proportional to the cube of its orbital radius
Define Lenz’s law
An induced current is always in a direction so as to oppose the change that caused it.
Define magnetic field
A region surrounding a magnet or current-carrying wire that will exert a force on any other magnet or current-carrying wire placed within it
Define magnetic flux
A value which describes the magnetic flues or field lines passing though an area. It is the product of magnetic flux density and the perpendicular area it passes through.
Define magnetic flux density
The force per unit current per unit length on a current-carrying wire placed at 90 degrees to the field lines. Sometimes referred to as the magnetic field strength
Define magnetic flux linkage
The magnetic flux multiplied by the number of turns, N, of the coil
Define motor effect
When a current-carrying wire is placed within a magnetic field (non-parallel to the field lines) and experiences a force perpendicular to both the wire and the field lines.
Define permittivity of free space
A measure of the ability of a vacuum to allow an electric field to pass through it
Define polarised
An atom/molecule becomes polarised when an external electric field causes the negative electron cloud to be shifted in the opposite direction to the positive nucleus - the charges are pulled in opposite directions ( this is what happens to the molecules of the dielectric in a capacitor).
Define potential gradient
The change of potential per metre at a point in the field
Define radial field
A field in which the field lines are all directed towards a single point (e.g. the centre of a planet or a point charge)
Define relative permittivity
The ratio of charge stored in a capacitor with the dielectric to charge stored without the dielectric. Also sometimes referred to as the dielectric constant
Define step-down transformer
A device made of two insulated wires coiled around an iron core in which the output voltage is smaller than the input voltage due to the secondary coil having fewer turns than the primary coil.
Define step-up transformer
A device made of two insulated wires coiled around an iron core in which the output voltage is greater than the input voltage due to the secondary coil having more turns than the primary coil.
Define synchronous orbit
An orbit in which the period of the orbit is equal to the rotational period of the object that it is orbiting
Define time constant
The time taken for a capacitor to discharge to 37% (e to the power of -1) of its initial charge. The time constant is equal to the product of the capacitance and the resistance of the fixed resistor (that the capacitor is being discharged through)
Define uniform field
A field in which all of the field line are parallel and equally spaced - field strength is equal in all areas of the field
