Electric and Magnetic Fields Flashcards
Define electric field strength.
Force per unit positive charge
E = F/Q
What unit is used for electric field strength?
N C^-1
Potential gradient =
Electric field strength
V/d
What creates electric fields?
Electric charges
Unit for magnetic flux
Weber - Wb
Unit for magnetic flux density
Tesla
Faraday’s Law of electromagnetic induction
The magnitude of induced e.m.f. is equal to the rate at which the magnetic flux is cut
Lenz’s Law
The direction of any induced current is in a direction that opposes the flux change that causes it
A.C. Generator
A generator that, via the use of slip rings, produces an alternating e.m.f. and so an alternating current
Alternating current
Electric current that reverses its direction with a constant frequency.
Ammeter
A device used to measure electric current, connected in series with the components
Conductor
A material with a high number density of conduction electrons and therefore a low resistance
Conventional current
A model used to describe the movement of charge in a circuit.
Conventional current travels from + to -
Coulomb’s law
The force between to charges is proportional to the product of the charges and inversely proportional to the square of the distance between the charges
Efficiency
The ratio of useful output energy to total input energy
Electric charge (Q or q)
Current x Time
Measured in Coulombs (C). Scalar quantity
Electric current
A flow of charge
Vector quantity, measured in amperes (A)
Electric field strength (E)
Force per unit charge
Given by E=F/q
Measured in N C^-1
Electric field
A region of space where a charged particle experiences a force
It goes from + to -
Electromagnetic Induction
The process of inducing e.m.f. using a magnetic field and a changing flux linkage
Electromagnetic wave
A self-propagating wave that does not require a medium to travel through
E.m.f.
The electrical energy transferred per unit charge when one form of energy is converted into electrical energy
Measured in volts (V)
Electron flow
The movement of electrons (usually around a circuit), from - to +
Electronvolt
One electronvolt is the energy change of an electron when in moves through a potential difference of one volt
Fleming’s LEFT hand rule
Used with electric motors and forces acting on moving charges in magnetic fields
It shows the direction of force on a conductor carrying a current in a magnetic field.
Force - thumb, field - first finger, current - second finger, all at right angles to each other
Fleming’s RIGHT hand rule
Used with generators and electromagnetic induction
It shows the direction of the induced current when a conductor moves through a magnetic field
Force - thumb, field - first finger, current - second finger, all at right angels to each other
Induced e.m.f.
The e.m.f. produced by electromagnetic induction
Insulator
A material with a small number density of conduction electrons and therefore high resistance
Lenz’s law
When a magnet is moved in a coil of wire, the coil has an induced e.m.f.
If connected in a circuit, the coil itself produces a magnetic field. This magnetic field opposes the magnet
Define magnetic flux
The product of magnetic flux density and the area at right angles to the flux
Define ampere
SI unit for electric current
What is alternating current?
Electric current that reverses its direction with a constant frequency
What is an a.c. generator?
A generator that, via the use of slip rings, produces an alternating emf and so an alternating current
Define magnetic flux density
The strength of the magnetic field
Define magnetic flux
The product of magnetic flux density normal to a circuit and the cross-sectional area of the circuit.
Define magnetic flux linkage
The product of the magnetic flux and the number of turns
Define intensity
Power per unit cross-sectional area
Define what is meant by a uniform electric field
A region between two objects of different electric potential in which a charged particle will feel a force and the strength of the force is the same at any point in the field.
Field lines are equispaced.
What is a magnetic field?
Region where a force is exerted on magnetic material
Field lines go from north south (direction a north pole would feel a force in the field).
What is the law of conservation of charge?
Electric charge cannot be created or destroyed
Positive and negative charges can make each other neutral
