basic laws ohm’s law kirchhoff’s law series resistors & voltage division parallel resistors...
Post on 21-Dec-2015
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BASIC LAWS
• Ohm’s Law
• Kirchhoff’s Law
• Series resistors & voltage division
• Parallel resistors & current division
• Y - transformation
Ohm’s Law
Property of a material to resist a flow of current known as resistance
A
lR - measured in ohms ()
- Resistivity of the material
l - length of the material
A - Cross section area of the material
Mathematically,
+ V
i
Ohm’s Law
Ohms’s Law: A voltage across a resistor is directly proportional to the current flowing through a resistor
+ V
i
v i
Constant of proportionality between v and i is the resistance, R ()
v = i R
Must comply with passive sign convention
Ohm’s Law
Fixed resistors
Wirewound type
carbontype type
Ohm’s Law
Variable resistors
Ohm’s Law
Two extreme values of resistance:
Short circuit
Open circuit
0i
0
i
vR
o
v
i
vR
Ohm’s Law
Conductance: reciprocal of resistance
v
i
R
1G - measured in siemens (S)
Conductance: ability of an element to conduct current
Ohm’s Law
Power in a Resistor
vip
+ V
i
Rii)iR(p 2R
v)
R
v(vp
2
Always absorbs power
Always positive
Kirchhoff’s Law
Network topology
A branch represents a single element such as a voltage source or a resistor.
Kirchhoff’s Law
Network topology
A branch represents a single element such as a voltage source or a resistor.
A node is the point of connection between two or more branches.
Kirchhoff’s Law
Network topology
A branch represents a single element such as a voltage source or a resistor.
A node is the point of connection between two or more branches.
A loop is any closed path in a circuit.
Kirchhoff’s Law
Network topology
Two or more elements are in series if they exclusively share a single node and consequently share the same current
Two or more elements are in parallel if they are connected to the same two nodes and consequently have the same voltage across them
1 & 2 - parallel
10V & 4 - parallel
5 in series with (1 and 2 in parallel)
Kirchhoff’s Law
Kirchhoff’s Current Law (KCL)
Kirchhoff’s current law (KCL) states that the algebraic sum of currents entering a node (or a closed boundary) is zero
01
N
nniMathematically,
Kirchhoff’s Law
Kirchhoff’s Voltage Law (KVL)
Kirchhoff’s voltage law (KVL) states that the algebraic sum of all voltages around a closed path (or loop) is zero.
Mathematically, 01
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