Faculty of Engineering
Mechatronics Dept.
ELECTRICAL CIRCUITS 1(EPE 112)
FALL (2021 - 2022) – LEVEL 1
Chapter 2
Resistance
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Resistance
The resistance (R) of an element denotes its ability to resist the flow of electric current (I)
; it is measured in ohms (𝛀).
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Ohm’s law
Ohm’s law states that the voltage v across a resistor is directly proportional to the
current i flowing through the resistor.
Georg Simon Ohm (1787–1854)
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Ohm’s law (cont.)
A short circuit is a circuit element with resistance approaching zero.
An open circuit is a circuit element with resistance approaching infinity.
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TYPES OF RESISTORS
Fixed Resistor
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CONDUCTANCE
Conductance is the ability of an element to conduct electric current; it is
measured in mhos (℧) or Siemens (S).
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SOLVED EXAMPLES:
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SOLVED EXAMPLE:
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CIRCUIT TOPOLOGY
Topology: How a circuit is laid out.
A branch represents a single circuit (network) element; that is,
any two terminal element. such as a voltage source or a resistor
5 branches
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CIRCUIT TOPOLOGY (CONT.)
A node is the point of connection between two or more branches.
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CIRCUIT TOPOLOGY (CONT.)
A node: is usually indicated by a dot in a circuit. If a short circuit (a connecting wire) connects two nodes, the two
nodes constitute a single node
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CIRCUIT TOPOLOGY (CONT.)
3 nodes
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CIRCUIT TOPOLOGY (CONT.)
A loop is any closed path in a circuit (network).
• A loop is said to be independent if it contains a branch which is not in
any other loop.
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CIRCUIT TOPOLOGY (CONT.)
For a network with b branches , l independent loops, and n nodes
𝒃=𝒍+𝒏−𝟏
Example:
7
1 2 6
𝒃= 9
𝒏= 5
0
DC 3 4 5 2A
𝒍= 5
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SERIES RESISTOR AND VOLTAGE DIVISION
Two of more elements are in series if they share a single node and then they carry the same current.
PARALLEL RESISTANCE AND CURRENT DIVISION
Two of more elements are in parallel if they connected to the same nodes and then they have the same voltage
across them
PARALLEL RESISTANCE AND CURRENT DIVISION (CONT.)
Short circuit Open circuit
SOLVED EXAMPLE:
SOLVED EXAMPLE:
SOLVED EXAMPLE (CONT.):
SOLVED EXAMPLE:
SOLVED EXAMPLE (CONT.):
SOLVED EXAMPLE:
SOLVED EXAMPLE (CONT.):
DR MOHAMMED KAMAL
MKHASSAN@HORUS.EDU.EG
