Experiment 4: DC Circuits BACKGROUND AND THEORY The resistance R of a metallic conductor is defined by R = Voltage Current = V I (4.1) where V is the potential difference applied between the endpoints of the conductor and I is the current flowing through the conductor.For a metallic conductor, such as a copper wire, the resistance R is a constant provided that the temperature of the wire stays essentially constant, that is R does not depend on I or V. Units: V is measured in volts (V), I in Amperes (A) or milli-amperes (mA), and R in Ohms (?).PROCEDURE www.lib-go.com Uploaded by Rasha Daoud to Lib-Go.com 49 Part A: DC Circuit with One Resistor 1.We can test if a material is ohmic or not by measuring the potential difference V across the material against www.lib-go.com Uploaded by Rasha Daoud to Lib-Go.com 48 a current I that pass through it while keeping the temperature of the material constant.1: Example of Ohmic and Non-Ohmic Materials Conductors obey Ohm's law and are called ohmic materials.Figure 4.

Experiment 4: DC Circuits
BACKGROUND AND THEORY
The resistance 𝑅 of a metallic conductor is defined by
𝑅 =
𝑉𝑜𝑙𝑡𝑎𝑔𝑒
𝐶𝑢𝑟𝑟𝑒𝑛𝑡 =
𝑉
𝐼
(4.1)
where 𝑉 is the potential difference applied between the endpoints of the conductor and 𝐼 is
the current flowing through the conductor.
For a metallic conductor, such as a copper wire, the resistance 𝑅 is a constant provided that
the temperature of the wire stays essentially constant, that is 𝑅 does not depend on 𝐼 or 𝑉.
Units: V is measured in volts (V), I in Amperes (A) or milli-amperes (mA), and R in Ohms
(Ω).
Figure 4. 1: Example of Ohmic and Non-Ohmic Materials
Conductors obey Ohm’s law and are called ohmic materials. On the other hand
materials that do not obey Ohm’s law are called non-ohmic materials. We can test if a
material is ohmic or not by measuring the potential difference 𝑉 across the material against
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a current 𝐼 that pass through it while keeping the temperature of the material constant. If 𝑉
does not depend linearly on 𝐼, then the material is not ohmic.
Equivalent Resistance of Two Resistors
Consider two resistors 𝑅1 and 𝑅2 connected in series, then these resistors can be
replaced by a single equivalent resistor 𝑅𝑠 where
𝑅𝑠 = R1 + R2
(4.2)
If the two resistors are connected in parallel, then they are equivalent to a single resistor of
magnitude 𝑅𝑃 where
1
𝑅𝑃

1
𝑅1
+
1
𝑅2
𝑜𝑟 𝑅𝑝 =
𝑅1𝑅2
𝑅1 + 𝑅2
(4.3)
Figure 4. 2: Two resistors connect in series (left) and in parallel (right).
Figure 4.2 shows how two resistors are connected in series and in parallel. When the two
resistors are connected is series, the current passing through them is the same, while when
they are connected in parallel, the potential difference (voltage) across their end points is
the same.
The uncertainty in 𝑅 (Δ𝑅) is given by
Δ𝑅
𝑅

Δ𝑉
𝑉
+
Δ𝐼
𝐼
(4.4)
APPARATUS
DC power supply, two resistors, Variable resistor, Ammeter, Voltmeter.
PROCEDURE
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Part A: DC Circuit with One Resistor

1. Connect the following circuit using only one resistance either R1 or R2. (You are
   provided with a 4 or 5 volt power supply).
   Figure 4.3: DC circuit with one resistor.
   Note:
   You should not connect the circuit to the power supply until it is approved by
   your instructor