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ELECTRICITY Flashcards

1
Q

Conductor

A

a material which will tend to allow a flow of electrons

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2
Q

insulator

A

a material which tends to restrict the flow of electrons

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3
Q

coulombs law

A

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

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4
Q

electric field strength

A

force per unit positive charge at a point in an electric field

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5
Q

potential difference

A

between two points is the work done in moving a unit positive charge from one point to the other

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6
Q

the volt

A

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

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7
Q

the capacitance

A

of a body is defined as the ratio of the charge (Q) on a body to its potential (V)

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8
Q

the farad

A

a body has a capacitance of 1farad if the addition to the body of 1 coulomb raises the potential of the body by 1volt

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9
Q

ohms law

A

states that for a metallic conductor at constant temperature, the current will be proportional to the voltage

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10
Q

the resistance

A

of an object within an electrical circuit is defined as the ratio of the voltage across it to the current flowing through it

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11
Q

the ohm

A

a conductor has a resistance of 1ohm if a current of 1amp flows when a voltage of 1volt is applied

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12
Q

the resistivity

A

of a material is the resistance of an object of that material with unit area and unit length

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13
Q

joules law

A

states that the rate at which heat is produced by an electric current is proportional to the square of the current

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14
Q

semiconductor

A

a material whose resistivity lies between that of a conductor and an insulator

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15
Q

current-carrying conductor

A

in a magnetic field experiences a force

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16
Q

magnetic flux density

A

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

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17
Q

the ampere

A

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

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18
Q

faradays law

A

States that the size of the induced emf is directly proportional to the rate of change of flux

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19
Q

lenzs law

A

states that the direction of an induced current is such as to oppose the change causing it

20
Q

Electric fields

A

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

21
Q

Electric field line

A

A line drawn in an electric field showing the direction of the force on a positive charge placed in a field

22
Q

Ion

A

An atom or a molecule that has lost or gained one or more electrons

23
Q

Holes

A

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

24
Q

Intrinsic conduction

A

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.

25
Thermistor
A semiconductor devise whose resistance decreases rapidly with increasing temperature
26
Light dependant resistor (LDR)
A semiconductor whose conductivity is increased when light shines on it
27
Doping
The adding of small controlled amounts of certain impurities to a pure semiconductor to increase its conductivity
28
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
29
P-type semiconductor
A semiconductor in which the impurity added produces extra holes which are available for conduction e.g. boron in silicon
30
Extrinsic conduction
Increased conduction in a semiconductor due to the addition of impurities is called extrinsic conduction.
31
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
32
Forward biased
A forward biased p-n junction conducts current
33
Reverse biased
A reverse biased p-n junction does not conduct current
34
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
35
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
36
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
37
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
38
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
39
Electromagnetic induction
Whenever a magnetic field passing through a coil changes, an emf appears in the coil. This phenomenon is called electromagnetic induction
40
The Weber
Is the magnetic flux density over an area of 1m^2 is 1T then the flux through the area is 1 Weber
41
Electric generator
A device that converts mechanical energy to electrical energy
42
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
43
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
44
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
45
Transformer
A device used to change the value of an alternating voltage

Physics (6 decks)

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