Download Lab#03 - 2nd Semester Notes

Ohm’s Law
Lab#03
LAB#03
OBJECTIVE
To investigate the relationship between the three variables R, V & I using Ohm’s Law.
EQUIPMENT REQUIRED
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Multi Meter
DC Power Supply
Different Valued Resistors
Bread Board
THEORY
BREAD BOARD
A breadboard is used to make up temporary circuits for testing or to try out an idea. No
soldering is required so it is easy to change connections and replace components. Parts will not
be damaged so they will be available to re-use afterwards.
CONNECTIONS ON BREADBOARD
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The top and bottom rows are linked horizontally all the way across as shown by the red
and black lines on the diagram.
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Ohm’s Law
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Lab#03
The other holes are linked vertically in blocks of 5 with no link across the centre as
shown by the blue lines on the diagram.
OHM’S LAW
The most applied relation in current electricity is that known as Ohm's Law. This principle states
that the potential difference or voltage drop V across a circuit component is proportional to the
electric current I which passes through it, the proportionality constant being defined as the
resistance R of the conductor:
V = RI
The unit of resistance is appropriately called the ohm. Thus R is in ohms when V is in volts and I
is in amperes. In an electrical circuit with two or more resistances, Ohm's law may be applied to
the entire circuit, to a portion of the circuit, or even to each individual resistance of the circuit.
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Ohm’s Law
Lab#03
PROCEDURE
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Choose one of the resistors that you have been given. Using the chart at the bottom of this
page or your notes, decode the resistance value and record that value in the first column
of the Table.
Figure 3.1
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Construct the circuit above, leaving the wire between the resistor and the battery
unconnected.
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Set the DMM to the 20 MA range, noting that the red lead should be connected to the
plug on the DMM designated for "MA" or "A". The black lead should always be
connected to the "COMMON" plug. When your circuit has been approved, connect the
remaining wire and read the current that is flowing through the resistor. Record this value
in the second column of the Table.
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Now replace the original resistor with the remaining resistors, one at a time, each time
recording the resistance value and the current you measured.
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When you have completed measuring all of the currents, disconnect the meter and
connect the circuit shown below. Change the meter to the 2VDC scale (or 2000 mV) and
move the red lead to the plug on the meter that indicates "V". Measure and record the
voltage across the resistor for each of the resistors. (On the 2000 mV scale, the decimal
point is for millivolts.)
Figure 3.2
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Ohm’s Law
Lab#03
OBSERVATIONS
Table 3.1
Resistance

Current
A
Voltage
V
Voltage/Resistance
V/
EXERCISE
Q1) Construct a graph of Current (vertical axis) Vs Resistance.
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Ohm’s Law
Lab#03
Q2) Construct a graph of Current (horizontal axis) Vs Voltage.
Q3)From your graph, what is the mathematical relationship between Current and Resistance (for
a constant voltage)?
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Q4)From your graph, what is the mathematical relationship between Current and Voltage (for a
constant resistance)?
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Q5) Ohm's Law state that current is equal to the ratio of voltage/resistance. Does your data
concur with this?
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Ohm’s Law
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Q6) Using Ohm’s Law find the value of the quantity omitted across each line of the following
table.
Voltage
V
Current
A
0.42 A
1.41 KV
90 mV
120 V
Resistance
W
200 
470 K
3.6 mA
8 mA
1.5 M
4.7 K
Q7) What is the value of this resistor, in ohms Ω?
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