Physics 1BL
K
IRCHOFF
’
S
R
ULES
Winter 2010
Page 1
Introduction
In this lab we will examine more complicated circuits. First, you will derive an expression for
equivalent resistance using Kirchhoff’s Rules. Then you will discuss the physics underlying
Kirchhoff’s rules. Then you will practice drawing circuit diagrams from real circuits and vice
versa. Finally, you will use Kirchhoff’s rules and your knowledge of equivalent resistance to
analyze complex circuits.
Prelab questions:
How to read Resistor Color Codes
First, find the tolerance band. It will typically be gold ( 5%) or silver (10%).
Starting from the other end, identify the first band  write down the number associated with that
color; in this case Brown is 1.
Now 'read' the next color. Here it is blue, so write down a '6' next to the 1. (you should have '16'
so far.)
Now read the third, or 'multiplier', band and write down that number of zeros.
(It is called a
multiplier band because you are multiplying the first two bands by 10 to the power of the number
of the third band.)
In this example the multiplier band is Red (2) so the multiplier is 10
2
.
The resistor value is 16 x
10
2
ohms or 1600
Ω
or 1.6k
Ω
.
If the multiplier band is Gold move the decimal point one place to the left. If the multiplier band
is Silver, move the decimal point two places to the left.
The tolerance band tells you how close to the stated value you can expect the actual resistance to
be. Gold indicated 5% tolerance and Silver indicated 10% tolerance. Therefore, Gold tolerance
resistors are between 95% and 105% of the value indicated by the color bands.
If the resistor has one more band past the tolerance band, it is a Quality band. The Quality band
indicates the failure rate of the resistor when operated at full power.
#
Color
Mnemonic
0
Black
Big
1
Brown
Boys
2
Red
Race
3
Orange
Only
4
Yellow
Young
5
Green
Girls
6
Blue
But
7
Violet
Violet
8
Gray
Generally
9
White
Wins
1
st
digit
2nd digit
x10
___
Multiplier
First digit
Second digit
Multiplier
Tolerance
Quality
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Physics 1BL
K
IRCHOFF
’
S
R
ULES
Winter 2010
Page 2
1.
Resistor color codes:
a.
What is the resistance of a resistor with the band colors Red Red Brown?
b.
What is the resistance of a resistor with the band colors Green Black Orange?
c.
What colors would you see on a 75 k
Ω
resistor?
d.
What colors would you see on a 500
Ω
resistor?
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 Spring '10
 staff
 Physics, Resistance, Resistor, power supply, equivalent resistance, Kirchoff’s Rules

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