L5. Electrical Resistance of a Wire
Armando Luquin
Name: ____________________
SIM LINK: https://phet.colorado.edu/sims/html/resistance-in-a-wire/latest/resistance-in-awire_en.html
1. First play with the SIM sliders and note how you can adjust the resistivity in Ohm cm, the
length of the wire in cm, and the cross-sectional area in cm2. When you move these see
that the resistance value is shown.
2. As the Length increases, what happens to the Resistance?
resistance increase
3. As the length increases, what happens to the resistivity?
resistivity is not affected by length
4. If you decrease the resistivity what happens to the resistance?
resistance also decreases
5. If you decrease the cross-sectional area, what happens to the resistance?
resistance increases
6. If you increase the cross-sectional area, what does this do to the wire’s shape?
wire's shape becomes thick
7. If you increase the cross-sectional area, what happens to the resistance?
resistance decreases
8. If you change the resistivity does this change the length of the wire?
length is not affected
9. If you change the resistivity does this change the area of the wire?
Area remains unchanged
10. If you change the length of the wire does the area change?
The cross-sectional area remains unaffected but the wire it is enlarged
11. Write an equation resistance R in terms of the resistivity (), length (L), and area (A).
p*L
Equation: R = ______________
A
12. Experiment to find the resistivity of a wire. Your values chosen for the resistivity and
the area can’t be the same as other pairs. Leave  and A set at some value, doesn’t
matter what it is. Do not change these two.
0.67
5.45
 = 
 = 
Now vary L and record the value of R in the table. Continue until you have filled in the
table.
Length in cm
Resistance in Ohms
2
0.246
4
0.492
6
0.739
8
0.985
10
1.231
12
1.477
18
2.215
13. Now use Excel or another graphing program to graph the L on the x-axis and R on the yaxis. Be sure to label your axes.
14. Find the trendline and record the equation of the line and the slope (be sure to keep
track of units). (Excel isn’t so good at that or I am not that good at Excel). Remember
equation of a line is of the form: y = (slope) x + b where b is where the line hits the yaxis.
y=0.1231x+0.0002
Equation: _________________________________
0.1231
Slope = _________
Since the slope is R/L, find the resistivity of the wire using your equation. Show your
work.
Is the resistivity you found the same as you set it in the simulation? If no try again.
Screenshot your graph and attach the plot in the space provided below:
15. Set L = 20 cm and  = 1 Ohm cm. What happens to R as the area gets smaller?
This is why it is very dangerous to use a small cross-sectional area extension cord on a
high-current appliance such as a space heater. The resistance can cause so much heat
that the insulation on the cord melts and a fire starts. Always check the current rating of
the extension cord and match it to the appliance.