Download Form5-1 Resistance

Theme 6 – Electricity at home
Aim : Experiment to investigate the dependence of
resistance on length of conducting wire.
OBJECTIVE: The object is to study the dependence of resistance
on the diameter, material and length of wire connected between the
pairs of the terminals.
Focus Questions

What are the factors that affect the resistance of a
material ?

What do you need to measure in order to find the
resistance?

Do different materials have the same or different
resistance?

Do you expect the resistance of a substance to increase
or decrease with
I.
Increase in length
II. Increase in cross section area (thickness)

Is the change of resistance of electrical devices used in
applications?

Can you give some examples?
Safety: The power supply output should be turned down
between readings to minimize heating of the resistors.
Heat causes the resistance to increase and this could
decrease the accuracy of your results. Coil A is made of
nichrome wire of diameter 0.35 mm. Coil B is made of nichrome
wire of diameter 0.18 mm. Coil C is made of Copper wire of
diameter 0.35 mm. They all have same length.
Ninu Cremona Lyceum – Gozo College – Physics Department
Page 1
Date: ____________
Theme 6 – Electricity at home
Aim : Experiment to investigate the dependence of
resistance on length of conducting wire.
Apparatus : D.C. power supply, wire, variable resistor, ruler,
switch, ammeter , voltmeter, various wires, different coils of wires.
Sources of error and precautions 1.
2.
Method
1. Part A - Connect the wire to the power supply. Adjust
the power supply voltage so that a current of 0.5 Amps
or less flows through the circuit.
2. Record the voltages and currents for lengths, of the
wire of 20, 40, 60, 80, and 100 cm. Simply press the end
of one of the voltmeter leads to the wire to make contact for
a voltage reading. Press at different points along the wire to
change the length.
3. Calculate the resistances of the various lengths of wire
(using V=IR). Note whether the incremental change in
resistance is nearly constant.
4. Part B – Now connect the coil A . Record the voltages
and currents for the coil. Calculate the resistance for
this coil of wire using Ohm's law.
5. Repeat this procedure for coils B and C. Be sure to
write down the specifications of the wires connected
between each pair of terminals.
Results :
Ninu Cremona Lyceum – Gozo College – Physics Department
Page 2
Table 1
Length of wire
in cm
0
Voltage - v
Current - I
0
0
Resistance =
V/I
0
20
40
60
80
100
Table 2
Coil of wire
Material,
Diameter and
length of wire
A
B
C
Nichrome
wire of
diameter 0.35
mm.
Nichrome
wire of
diameter 0.18
mm.
Copper
wire of
diameter 0.35
mm.
Voltage - v
Current - I
Resistance =
V/I
1. Fill in table 1 and 2 by calculating the resistance.
Determine the length of coil a from the resistance
measured. Coils B and C are the same length as coil A.
2. Plot a graph of resistance against length for data from
Table 1. As best as you can, fit a straight line through
the points.
Ninu Cremona Lyceum – Gozo College – Physics Department
Page 3
Conclusion/Evaluation
1. Describe or express in some way the relation
between the resistance of a conductor and its length
as illustrated by your graph. Is this relation clearly
visible from the graph?
2. How would you expect that the resistance of a
conductor changes with different materials,
different diameter and length of wire used.
3. Does your results support this relation: in particular,
do the resistance values of your coils support the
dependance of R on each of the three parameters
material,diameter and length.(HINT: compare coils
that differ by only one parameter)
4. As always, identify the sources of experimental
uncertainty in this experiment, and consider how
these uncertainties affect your results.
Ninu Cremona Lyceum – Gozo College – Physics Department
Page 4