Year 11 VCE Physics
Experiment - Factors affecting the resistance of a wire.
Background information:
All conductors resist the flow of current. This is called the resistance of the conductor. There are several factors that influence how much resistance is provided by a conductor: atomic/molecular structure of the metal, length and cross-section area.
Part 1: Investigating the effect of length on resistance
Procedure
1.
Cut 1 strand of nichrome wire of length 100cm. You will need a very thin wire for this part, so choose SWG 30 or SWG 26 (wire ID numbers).
2.
Insert the ends of the wire into two separate electronics mounts and stretch them out so that the wire cannot loop back on itself and create a short circuit. Ensure that there is little if any overhang where the ends of the wire are held in place by the screw-down plugs.
3.
Connect the nichrome wire to a power pack set at 2 volts. Measure and record the current and the voltage drop along the length of the wire.
4.
Loosen the screw-down plug at one end of the wire and pull the wire through so that the length of wire between the plugs is now only 80cm.
5.
Repeat steps 4 and 5 for 60cm, 40cm and 20cm lengths.
Results
Record your results in a suitable table. Calculate the resistance for each length of wire.
Wire 10 Wire Length Current number (m) (A)
Voltage
(V)
Resistance
(

)
SWG30
Analysis and Discussion
Plot a graph of resistance vs. length.
Describe the relationship between wire length and resistance.
Part 2: Investigating the effect of cross-section area on resistance
Procedure
1.
Cut 5 strands of nichrome wire, of different thicknesses. Ensure that each of your strands has the same length. Record this length. To minimise waste, cut 4 new wires (about 50 cm long) and re-use your wire from Part 1.
2.
Insert the ends of the thinnest wire (SWG 30) into 2 separate electronics mounts as done in Part
1, ensuring that there is little if any overhang. Measure the length of the wire. With each successive wire, ensure that it is the same length. (You may use blu-tack to stick the electronics mounts to the bench.)
3.
Connect the nichrome wire to the power pack on 2.0 V, and measure the voltage and current for the nichrome wire.
4.
Repeat steps 2 and 3 for each of your wire strands.

Results
Calculate resistance, cross-section area and length/area for each wire.
Wire ID
Diameter
(mm)
Length
(m)
Voltage (V) Current (I)
Resistance
(W)
Cross-section
Area (m 2 )
Length (m)
/Area (m 2 )
SWG 30 0.315
SWG 26 0.457
SWG 22 0.711
SWG 20 0.914
SWG 18 1.219
Analysis and Discussion

Plot a graph of resistance vs. cross section area and fit a trendline to it.

Comment on the nature of the mathematical relationship that this graph shows.

Transform the data and plot another graph to confirm the mathematical relationship.

Finally, plot another graph showing: Length (m) resistance vs. Length (m) / Area (m
2
)

Apply a linear trendline to this graph and display the equation. The gradient of this graph gives the resistivity (

) of nichrome. State your experimentally determined value for the resistivity of nichrome. Can you confirm this is correct by finding a reputable online source of information?
Conclusion
Write an overall conclusion for the experiment stating the effect on resistance of the two factors investigated and your calculated value for the resistivity of nichrome.