Download EE1000 Spring 2015, Lecture 3 (January 20, 2015)

EE1000, Lecture 3
Resistance, Ohms Law, Schematics, Color Code, Series/Parallel
Electric Terms:
Ohm's law: V = I R
Series circuits
A series circuit is a circuit in which resistors are arranged in a chain, so the current has only one
path to take. The current is the same through each resistor. The total resistance of the circuit is
found by simply adding up the resistance values of the individual resistors:
Equivalent resistance of resistors in series: R = R1 + R2 + R3 + ...
A series circuit is shown in the diagram above. The current flows through each resistor in turn. If
the values of the three resistors are:
With a 10 V battery, by V = I R the total current in the circuit is:
I = V / R = 10 / 20 = 0.5 A. The current through each resistor would be 0.5 A.
Parallel circuits
A parallel circuit is a circuit in which the resistors are arranged with their heads connected
together, and their tails connected together. The current in a parallel circuit breaks up, with some
flowing along each parallel branch and re-combining when the branches meet again. The voltage
across each resistor in parallel is the same.
The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the
resistance values, and then taking the reciprocal of the total:
Equivalent resistance of resistors in parallel: 1 / R = 1 / R1 + 1 / R2 + 1 / R3 +...
A parallel circuit is shown in the diagram above. In this case the current supplied by the battery
splits up, and the amount going through each resistor depends on the resistance. If the values of
the three resistors are:
With a 10 V battery, by V = I R the total current in the circuit is: I = V / R = 10 / 2 = 5 A.
The individual currents can also be found using I = V / R. The voltage across each resistor is 10
V, so:
I1 = 10 / 8 = 1.25 A
I2 = 10 / 8 = 1.25 A
I3=10 / 4 = 2.5 A
Note that the currents add together to 5A, the total current.
Resistor color-coding
To distinguish left from right: there is a gap between the C and D
bands.
Resistor Color Code Chart
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
Silver
None
1.
2.
3.
Temp.
Significant
Multiplier Tolerance Coefficien
figures
t (ppm/K)
0
0
×10
–
250 U
1
1
×10
±1% F 100 S
2
2
×10
±2% G 50
R
3
3
×10
–
15
P
4
4
×10
(±5%) – 25
Q
5
5
×10
±0.5% D 20
Z
6
6
×10
±0.25% C 10
Z
7
7
×10
±0.1% B 5
M
±0.05%
8
×108
A 1
K
(±10%)
9
×109
–
–
-1
–
×10
±5% J
–
-2
–
×10
±10% K
–
–
–
±20% M
–
Any temperature coefficient not assigned its own letter shall be
marked "Z", and the coefficient found in other documentation.
For more information, see EN 60062.
Yellow and Gray are used in high-voltage resistors to avoid metal
particles in the lacquer.
"Better Build a Roof Over Your Garage Before the Van Gets Wet."
Black Brown Red Orange Yellow Green Blue Violet Grey White
BBROYGBVGW
Examples
From top to bottom:
o
o
o
o
o
o
Green-Blue-Black-Brown: 56 ohms ± 1%
Red-Red-Orange-Gold: 22,000 ohms ± 5%
Yellow-Violet-Brown-Gold: 470 ohms ± 5%
Blue-Gray-Black-Gold: 68 ohms ± 5%
Brown, Black, Yellow, Silver: 100 kΩ, 10%
Red, red, blue, brown, brown: 2260 ohm, 1% (5 color bands)
The physical size of a resistor is indicative of the power it can dissipate, not
of its resistance. You can also download an android or iphone app.
********************************* Homework Assignment ******************************
*************************************************************************************
EE1000 HW #3
Name:
1. Find the resistance and tolerance of a resistor whose color bands are:
(a) blue, gray, orange, gold
%
(b) purple, green, black, silver
%
(c) white, brown, yellow
%
(d) green, purple, white, red, brown
%
(e) orange, gray, gold, gold
%
2. Find the equivalent resistance of the resistor combinations below
(a)
(b)
150Ω
(c)
150Ω
150Ω
100Ω
100Ω
100Ω
150Ω
3. Find the current (I) through each of the resistors, below.
(a)
(b)
+
3V
IR1 =
IR2 =
IR3 =
IR4 =
IR5 =
R1
100Ω
(c)
+
4V
R2
150Ω
R3
50Ω
+
4V
R4
50Ω
R5
150Ω