Electrostatatics
The study of fixed or stationary electric charge
Electrodynamics
The study of electric charges in motion
Electrification
Is the process of adding or removing electrons from a substance
Electrification can be created by
Contact
Friction
Induction
Electrostatic law # 1
Unlike charges attract; like charges repel
Electrostatic law # 2
Electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them (Coulomb's Law)
Electrostatic law # 3
When an object becomes electrified, the electric charges are uniformly distributed throughout the object or on its surface
Electrostatic law # 4
The electric charge of a conductor is concentrated along the sharpest curvature of its surface
What is the coulomb's law
Electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them F=k QaQb/d square
Name a device that applies the fourth law of electrostatics
Cattle Prod
Super conductor
Is the property of some materials to exhibit no resistance below certain critical temperature. Example: Niobium, Titanium
Conductor
Is any substance through which electrons flow easily. Most metals are good electric conductors; copper, aluminum
Semiconductor
Is a material that under some conditions behaves as an insulator and in other conditions behaves as a conductor. Example: Silicone and Germanium
Insulator
Is any material that does not allow electron flow. Wood , glass, cloth , rubber, plastic
What is the relation between electric resistance and electric current
Ohm's Law. Increasing electric Resistance result in reduced electric current
Unit of voltage
Volt (V)
Unit of Current
ampere(A)
Unit of Power
Watts (W)
Define Ohm's law
The voltage across the total circuit or any portion of the circuit is equal to the current multiplied by the resistance V= I x R
If a current of 2A passes through a conductor that has a resistance of 6 ohm, what is the voltage across the conductor?
V=IR
V=2A X 6 ohm =12
A kitchen toaster draws a current of 2.5 A. If the household voltage is 110V, what is the electric resistance of the toaster
V=IR
R=V/I
110V/2.5A= 44 Ohm
Formula to create the total resistance of a circuit in series
The total resistance is equal to the sum of the individual resistance RT = R1+R2+R3
The current through each circuit element is the same and is equal to the total circuit current IT=I1=I2=I3
The sum of the voltages across each circuit elements is equal to the total circuit voltage VT=V1+V2+V3
Circuit in parallel formulas
The sum pf the current through each circuit element is equal to the total circuit current IT=I1+I2+I3
The voltage across each circuit element is the same and is equal to the total circuit voltage VT=V1=V2=V3
The total resistance is the inverse of the sum of the reciprocals of each individual resistance 1/RT=1/R1+1/R2+1/R3
Example of parallel circuit
5,4,2 find the total resistance
1/RT=1/5+1/4+1/2
LDC 19/20
20/19 = 1.05
What is the difference between direct current and alternating current
Direct current the electron flow in one direction through the conductor
Alternating current the electron flow alternatively in opposite direction
Draw a graph to represent alternating and direct current
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What is the unit of electric power
Watts (W)
Define one watt
One watt is equal to one ampere of current flowing through an electric potential of 1 volt
P= I x V
Any charged particle in motion create a
Magnetic field
The lines of magnetic fields are always
perpendicular to the motion of the particle
What is the magnetic permeability
The ability of a material to attract the lines of magnetic field intensity
Explain paramagnetic materials
Slightly attracted to a magnet. The degree of magnetism exhibited by a material is related to the number of unpaired electron in the outer shells.
(contrast materials used in MRI)
Explain diamagnetic materials
Known as non magnetic. Weakly repelled by either magnetic pole. Can't be artificially magnetized. Example water and plastic
Explain ferromagnetic materials
Strongly attracted by magnet. Can be permanently magnetized. Examples are iron, cobalt , nickel and rare earth ceramics . An alloy of aluminum, nickel and cobalt called alnico is one of the more useful magnets produced.
Explain magnetic susceptibility
The degree to which various material can be magnetized . Ion has high magnetic susceptibility
The imaginary lines of the magnetic field leave the
north pole and enter the south pole
What is the SI unit of magnetic field strength
Tesla
What was the older unit used for magnetic field strength
Gauss
1 Tesla =
10,000 gauss
Helix
...
Solenoid
A coil of wire
Electromagnet
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Faraday's law
An electric current is inducted to flow in a circuit if some part of that circuit is a changing (moving) magnetic field
According to Faraday's law, the magnitude of the inducted current depends on four factors
Strength of the magnetic field
Speed at which the magnetic field moves
The number of turns in the conductor
Angle of the conductor to the magnetic field
Varying magnetic field intensity induced an
Electric current
What is the function of an Induction motor
Powers the rotating anode of an x- ray tube
What is the function of a transformer
Changes the intensity of alternating voltage and current
Autotransformer, step up transformer and step down transformer
Auto transformer: Self Induction
Step up transformer: Mutual Induction
Step down transformer: Mutual Induction
Advantage of a shell type transformer
Confines more on the magnet field lines of the primary winding because the secondary is wrapped around it and there are essentially two closed cores.
Transformer law
Transforms electric potential and current into higher or lower intensity
Vs/Vp=Ns/Np
Ns/Np is known as the turns ratio of the transformer
The secondary side of a transformer has 300,000 turns; the primary side has 600 turns. What is the ratio?
Ns = 300,000
Np = 600
300,000/600= 500:1
Copper loss
Energy dissipated by resistance in the wire used ,to wind a coil
Hysteresis loss
Magnetic friction in the core due to changing magnetic field
Eddy current loss
Power loss due to electric currents induced in the core