ELECTRICITY Flashcards
Conductor
a material which will tend to allow a flow of electrons
insulator
a material which tends to restrict the flow of electrons
coulombs law
states that the force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them
electric field strength
force per unit positive charge at a point in an electric field
potential difference
between two points is the work done in moving a unit positive charge from one point to the other
the volt
the potential difference between two points is 1Volt if the work done in moving a charge of 1coulomb from one point to the other is 1 joule
the capacitance
of a body is defined as the ratio of the charge (Q) on a body to its potential (V)
the farad
a body has a capacitance of 1farad if the addition to the body of 1 coulomb raises the potential of the body by 1volt
ohms law
states that for a metallic conductor at constant temperature, the current will be proportional to the voltage
the resistance
of an object within an electrical circuit is defined as the ratio of the voltage across it to the current flowing through it
the ohm
a conductor has a resistance of 1ohm if a current of 1amp flows when a voltage of 1volt is applied
the resistivity
of a material is the resistance of an object of that material with unit area and unit length
joules law
states that the rate at which heat is produced by an electric current is proportional to the square of the current
semiconductor
a material whose resistivity lies between that of a conductor and an insulator
current-carrying conductor
in a magnetic field experiences a force
magnetic flux density
is the force experienced by a conductor of length 1m carrying a current of 1A at right angles to the field. Its direction is the direction of the magnetic field lines
the ampere
is that current which, if maintained in two infinitely long wires of negligible cross-section placed one metre apart in a vacuum, would produce between the wires force of 2x10^-7 Newtons per metre length of the wire
faradays law
States that the size of the induced emf is directly proportional to the rate of change of flux
lenzs law
states that the direction of an induced current is such as to oppose the change causing it
Electric fields
An electric field is any region of space where a static electric charge experiences a force other than the force of gravity.
An electric field is always caused by other static charged in the vicinity
Electric field line
A line drawn in an electric field showing the direction of the force on a positive charge placed in a field
Ion
An atom or a molecule that has lost or gained one or more electrons
Holes
When an electron breaks free from a covalent bond, it leaves behind a gap in the atom from which it came. This gap is called a positive hole or simply a hole
Intrinsic conduction
Conduction in a pure semiconductor due to electrons moving from negative to positive and an equal number of holes moving in the opposite direction is called intrinsic conduction.
Thermistor
A semiconductor devise whose resistance decreases rapidly with increasing temperature
Light dependant resistor (LDR)
A semiconductor whose conductivity is increased when light shines on it
Doping
The adding of small controlled amounts of certain impurities to a pure semiconductor to increase its conductivity
N-type semiconductor
An n-type semiconductor is one in which the impurity added produces more free electrons available for conduction e.g. phosphorus in silicon
P-type semiconductor
A semiconductor in which the impurity added produces extra holes which are available for conduction e.g. boron in silicon
Extrinsic conduction
Increased conduction in a semiconductor due to the addition of impurities is called extrinsic conduction.
Junction voltage
The potential difference that exists across a p-n junction caused by holes and electrons moving across the junction when it was formed is called the junction voltage
Forward biased
A forward biased p-n junction conducts current
Reverse biased
A reverse biased p-n junction does not conduct current
Magnetic field
Any region of space where magnetic forces can be felt. The direction of the magnetic field at a point is the direction of the force On a North Pole if it were places at that point
Magnetic field line
A line drawn in a magnetic field so that the tangent to it at any point shows the direction of the magnetic field at that point
Right hand grip rule
States that if the right hand clasps a conductor with the thumb pointing in the direction of the current, then the fingers give the direction of the magnetic field around the conductor
Flemings left hand rule
States that if the thumb, first finger and second finger of the left hand are held at right angles, with the first finger pointing in the direction of the magnetic field and the second finger pointing in the direction of the current, then the thumb points in the direction of the force
Tesla
The magnetic flux density at a point is 1 Tesla is a conductor of length 1m carrying a current of 1A experiences a force of 1N when placed perpendicular to the field
Electromagnetic induction
Whenever a magnetic field passing through a coil changes, an emf appears in the coil. This phenomenon is called electromagnetic induction
The Weber
Is the magnetic flux density over an area of 1m^2 is 1T then the flux through the area is 1 Weber
Electric generator
A device that converts mechanical energy to electrical energy
Mutual induction
If a changing magnetic field in one coil causes an induced emf to appear in a nearby coil there is said to be mutual induction between the two coils
Self induction
Whenever the current passing through a coil changes, the magnetic field surrounding that coil changes. This changing magnetic field induces an emf in the coil that opposes the changing current
A.c. And inductors
A coil opposes the flow of direct current (d.c.) with its ohmic resistance.
A coil opposes the flow of alternating current (a.c.) with its ohmic resistance and the back emf induced in it
Transformer
A device used to change the value of an alternating voltage
