Experiment I
Ohm's Law
I. References
II. Equipment
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III. Introduction
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IV. Symbols
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Variable resistor
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Battery
Ammeter
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Resistor
Switch
Voltmeter
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V. Electrical Circuits
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V A − VB = ∆V AB = 0 ∆VBC = IR
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∆VCD = 0 ∆VDE = Ir
∆VEF = 0 ∆VFG = −ε
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∆V AA = IR + Ir − ε = 0
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ε = I (R + r)
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B I1
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I2
I = I1 + I2
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VI. Computing the Effective Resistance of Networks of Resistors
O
C
A
R1
I
R2
R1
R2
I1
I2
B
D
O'
(a)
5 6 +
(b)
5" 6
Series connection
Since current represents flow of
charge and therefore must be
conserved, the current in R1 must
be the same as the current in R2.
Hence
V1 = IR1
V2 = IR2
therefore
V1 + V2 = I ( R1 + R2 )
which is equivalent to
writing V = IR
where V = V1 + V2
and R = R1 + R2
i.e. two resistors connected in
series are equivalent to one
resistor whose value is equal to
their sum.
Generalizing, R = i Ri
Parallel connection
The potential difference V
between O and O ’ must be the
same whether we go along OABO
’ or OCDO ’. Also conservation
of current requires that
I = I1 + I 2
V
V
I2 =
I1 =
R2
R1
therefore
1
1
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I =V
R1 R2
which is equivalent to
writing V = IR
RR
where R = 1 2
R1 + R2
i.e. two resistors are connected in
parallel are equivalent to one
whose reciprocal is equal to the
sum of their reciprocals.
1
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Generalizing,
=
R
i Ri
VII. Experiment
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V = IR ε = I ( R + r )
which can be combined and rewritten as
V = ε − rI .
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Dimensions in inches
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Figure I-6: The 1N914 Switching Diode
Peak Reverse Voltage
75 V
Average Forward Rectified Current
75 mA
Peak Surge Current, 1 Second
500 mA
Continuous Power Dissipation at 25°C
250 mW
Operating Temperature Range
-65 to 175°C
Reverse Breakdown Voltage
100 V
Static Reverse Current
25 nA
Static Forward Voltage
1 V at 10 mA
Capacitance
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