Chapter 2-1
• Voltage and Current Sources
• Resistors
• Ohms Law
Current and Voltage Sources
Ideal Voltage Source: Maintains a fixed voltage at its
terminals regardless of the current flowing through it
Ideal Current Source: Maintains a fixed current through its
terminals regardless of the voltage at the terminals
Two types of ideal Sources
Independent Source: provides voltage or current in the
circuit that does not depend on other voltages or currents
in the circuit
Dependent Source (controlled source): provides
voltage or current in the circuit whose vales depend on
other voltages or currents in the circuit
Independent Sources
Dependent Sources
Which are Valid
Compute
1. Is it valid?
2. Which sources are delivering and absorbing power
What is alpha makes it valid
Resistance
Electrical Resistance: is the measure of a materials ability
to impede the flow of electrical charge
Resistor (R): is the circuit element that provide resistance,
unit of measure is in ohms
Conductance (G): is the reciprocal of resistance,
measured in Siemens.
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
Silver
Numeric 1 Numeric 2 Numeric 3 Multiplier
0
0
0
1
1
1
1
10
2
2
2
100
3
3
3
1K
4
4
4
10K
5
5
5
100K
6
6
6
1M
7
7
7
10M
8
8
8
9
9
9
0.1
0.01
Tolerance
±1%
±2%
±0.5%
±0.25%
±0.10
±0.05%
5%
10%
Four band Resistor
The first two bands indicate numeric
values.
Five band Resistor (High precision)
The first three bands are numerical
values.
The third band is the multiplier.
The fourth band is the multiplier.
The fourth band is the tolerance.
The fifth band is the tolerance.
Example:
[Red2][Green5][Yellow10k][Silver10%]
Example:
[Blue6][Gray8][Red2][Blue1M][Brown1%]
Resistor value = 25 x 10k = 250 kOhm 10%
Resistor value = 682 x 1M = 682 MOhm 1%
Type
Characteristics
Carbon
Least expensive, wide available range of values
and tolerances, typically used for low power and
low frequency applications
Metal Film
Used in higher voltage applications and where
high precision is called for. These devices exhibit
internal capacitance, due to the metal film
deposits, which can cause changes in the device
impedance at higher frequencies.
Wirewound
Used for medium to high voltage applications
requiring high power handling. However due to
their geometry they exhibit high inductive
properties, making them suitable only for lower
frequency applications.
Ohms Law
Ohm’s Law
Ohm’s Law gives a relationship between a material’s
resistance, R, the voltage across it, v, and the current flowing
through it, i.
v  iR
Find missing values and power dissipated in resistors
Find missing values and power dissipated in resistors
Find missing values and power dissipated in resistors
Now we have and expression for ohms
law and power
p  iv
p  i (iR )  i 2 R
v2
v
p   v 
R
R
Note: Resistors can only dissipate power in the circuit, not create
-- the resistor is an example of a passive circuit element --
What you should know
1. Voltage and Current Sources
2. Resistance. Conductance, and Resistors
3. Ohms law and applications
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