Electric Circuit, Resistivity, Resistance, Ohm’s
Law, Power Law, Kirchhoff’s Laws, mixed
Circuits, internal Resistance
Fundamentals of
ELECTRICAL ENGINEERING
Manfred Salamon
Jan 4th , 2015
Riyadh
Module TM-EP2
Course -EE1
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Electrical Engineering Basics Ohms Law, Lecture notes of Electrical Engineering
Electrical Engineering Basics Ohms Law
Typology: Lecture notes
2015/2016
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Electric Circuit, Resistivity, Resistance, Ohm’s
Law, Power Law, Kirchhoff’s Laws, mixed
Circuits, internal Resistance
Fundamentals of ELECTRICAL ENGINEERING Manfred Salamon Jan 4th , 2015 Riyadh Module TM-EP Course -EE
Electric Circuit A voltage source separates charges You get a + and a – pole When you connect the two poles of the source, you get an electric circuit Different charges tend to reverse the separation Charges will move in the circuit Either negative charges (electrons) or positive charges (ions) can move, i.e. charge carriers move. EE1 – Ohm- Kirchhoff
Structure of Matter
Why are some materials providing more free electrons than others? Atomic Bondin g EE1 – Ohm- Kirchhoff
EE1 – Ohm- Structure of Matter
Kirchhoff
Crystal A + Melt B Crystal A + Crystal B
Ions Electrons Drift Electrical resistance friction like flowing water in a tube Resistance depends on shape, size (geometry) and material A l R R = resistance (), = specific resistance, resistivity (mm2/m) l = length (m), A=area (mm2) EE1 – Ohm- Resistivity Kirchhoff
Crystal A + Melt B Crystal A + Crystal B
Material Resistivity (mm 2/m) pronounced roh Silver 0. Copper 0. Aluminum 0. Tungsten 0. Constantan (CuNi44) 0. Sea water 3* Earth 108 distilled water 1010 EE1 – Ohm- Resistivity Kirchhoff In some cases it is convenient to use the reciprocal value of resistivity which is called conductivity ϰ [pronounced kappa] its unit is (m/ mm2) ϰ = 1 / ρ Then A l R ϑ ϑ ΔR : Change in resistance R 20 : Resistance value at 20°C (reference!) α : Temperature coefficient of the material ( for metals in the range of ±0.04Ω/K) Δϑ : Change in temperature Resistivity is Temperature dependent!
Current Direction dinary electrical circuit consists of a source of voltage and/or current wh onnected by electrical conducting material, like metal wires, usually Cu provide a good electrical conductivity due to electrons which are free to n a normal electric circuit, electrons (with negative charge) move from the – (negative) to the + (positive) pole! ventional current direction is from the + (positive) to the – (negative) p Physical movement of electrons Technical direction
EE1 – Ohm- Kirchhoff
Current Strength
n e A
I
v
n e A v
t
n e A l
I
A l
n
V
n
n
t
n e
t
Q
I
c c c c
t Q I (^) A t C [ I ] Current strength means, how much charge flows in a certain time. A=Ampere, 1C = 1A 1s Electron density of available free electrons of a metal, a specific value. 22 3
- 5 10 nc cm V = velocity of electron flow For Cu at room temperatu EE1 – Ohm- Kirchhoff 11 The Current Density J= I/A [A/mm2] Is a measure for the strength of effect of current.
Crystal A + Melt B Crystal A + Crystal B
Ohm’s Law
An electric voltage causes a directional electric current Formal definitions: 1V is the voltage at a conductor if the resulting current is 1 A and the resulting heat power is 1W
The ratio of voltage by current is called
electrical resistance R
The relationship between U, I and R is called
Ohm’s law
I
U
R ^
A
V
[ ]
[ ]
[ ]
I
U
R = Ohm
EE1 – Ohm- Kirchhoff
Crystal A + Melt B Crystal A + Crystal B V U I R R U I U R I I U R EE1 – Ohm- Ohm’s Law Kirchhoff
Crystal A + Melt B Crystal A + Crystal B
P U I W U Q U I t P t 2 2 R U P U I I R W U Q U I t P t [P] = W = V A [W] = J = Ws = Vas, kWh P = power U = voltage I = current R^ = resistance EE1 – Ohm- Formulas Kirchhoff
Crystal A + Melt B Crystal A + Crystal B
Example of a DC resistance circuit EE1 – Ohm- DC Circuits Kirchhoff
Crystal A + Melt B Crystal A + Crystal B
R 1 R 2 Rv First Kirchhoff rule: The individual currents sum up to the total current Everywhere the same voltage implies I1 + … + Iv = Itotal v R total
U
R
U
R
U
R
U
1 2 v Rtotal R 1 R 2 Rv i 1 Ri 1 1 ... 1 1 1 v total R R R R 1 ... 1 1 1 1 2 Rule of current division v total total v R R I I EE1 – Ohm- Parallel Circuit Kirchhoff
Crystal A + Melt B Crystal A + Crystal B
Second Kirchhoff rule: The individual voltages sum up to the total voltage U 1
- … + Uv = Utotal Everywhere the same current I implies IR1+ … + IRv = Utotal = I*Rtotal v i total i v R R R R R 1 1 2 ... total i total i total i
R
R
R I
R I
U
U
Rule of voltage division EE1 – Ohm- Series Circuit Kirchhoff