Grade 10 Coulomb’s Law Lab
Instructions
Important Note: - If you do any work on Excel, you need to submit the Excel file also to get marks.
In this experiment, you will find the electrostatic force between two charged pith balls suspended by strings using
Coulomb’s Law. You will then correlate how the electrostatic force and the angle with the vertical of the string are
connected to another value in the experiment.
1. Click the link to the virtual lab Coulomb’s Law Lab.
(http://thephysicsaviary.com/Physics/Programs/Labs/CoulombsLawLab/)
2. Click Begin on the screen.
Experiment Procedure
1. Click Charge 1 and write down the charge and mass values for Pith Ball 1 in the table below. Click Charge 1
again to close that box. Click Charge 2 and write down the charge and mass values for Pith Ball 2 in the table
below. Click Charge 2 again to close that box.
Important: Ensure that the units are correct according to the table and write the values in scientific notation
correct to 2 decimal places.
Pith Ball 1
#
1.
2.
3.
4.
5.
6.
Charge
𝑸𝟏 (𝑪)
37.8*10^9C
37.8*10^9C
40.1*10^9C
40.1*10^9C
48.1*10^9C
48.1*10^9C
Pith Ball 2
Mass
𝒎𝟏 (𝒌𝒈)
7.3*10^-5
7.3*10^-5
7.3*10^-5
7.3*10^-5
7.3*10^-5
7.3*10^-5
Charge
𝑸𝟐 (𝑪)
37.7*10^9C
37.7*10^9C
37.7*10^9C
37.7*10^9C
37.7*10^9C
37.7*10^9C
Grade 10 Coulomb’s Law Lab
Mass
𝒎𝟐 (𝒌𝒈)
Distance
Between
Charges
𝒓 (𝒎)
Angle with
Vertical for
String 2
θ (˚)
7.3*10^-5
0.213 m
19.2
7.3*10^-5
0.242 m
16.2
7.3*10^-5
0.276 m
12.2
7.3*10^-5
0.236 m
17
7.3*10^-5
0.250 m
17.5
7.3*10^-5
0.225 m
22
Tan θ˚
Electrostatic
Force between
𝑸𝟏 and 𝑸𝟐
F (N)
0.348
2.83*10^-4 N
0.291
2.19*10^-4 N
0.216
1.79*10^-4 N
0.306
2.44*10^-4 N
0.315
2.61*10^-4 N
0.404
3.22*10^-4 N
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2. Click the left pointing blue arrows for Charge 1 and Charge 2 to move them
to their left extreme positions.
3. Click Show Grid, measure and write down the position of Charge 2 on the ruler in the table above in the
column “Distance Between Charges, r”. The value must be in scientific notation, in the correct units and to 3
decimal places. If the position of Charge 2 lies between two divisions, use estimation to be as accurate as
possible. Click Hide Grid to hide the ruler.
4. Click Show Angle to show the protractor and measure the angle the Charge 2’s string makes with the vertical.
If the angle of Charge 2 string lies between two divisions on the protractor, use estimation to be as accurate as
possible. Write the value of the angle to one decimal place in the column “Angle with Vertical for String 2”.
Click Hide Angle to hide the protractor.
5. Calculate and enter the value of tan θ˚ in the column Tan θ˚ rounded to two decimal places.
6. Use Coulomb’s Law to calculate the electrostatic force and write its value in in the last column. The value must
be in scientific notation, in the correct units and to 2 decimal places. This completes your observation 1.
7. Without changing the settings for the Charge 1 or Charge 2, use the right pointing blue arrows for Charge 2
and increase the distance between the charges. Measure the new distance r and the angle θ and record it in
your table as observation 2.
8. Without changing the settings for Charge 2, change the value of Charge 1 (without making it zero) and if
needed the distance r so that the angle θ is different from all previous observations. Measure the new
distance r and the angle θ and record it in your table as observation 3. Also write the values of both the
charges and their masses. (NOTE: The mass and charge of charge 2 remain constant throughout the
experiment.)
9. Without changing the settings for Charge 2 and with the same value of Charge 2 in step 8, change the
distance between the charges by using the right pointing arrows of Charge 2 so that the angle θ is different
from all previous observations. Measure the new distance r and the angle θ and record it in your table as
observation 4. Also write the values of both the charges and their masses.
10. Without changing the settings for Charge 2, once again change the value of Charge 1 only to a value different
from that in step 8 (without making it zero) so that the angle θ is different from all previous observations.
Measure the new distance r and the angle θ and record it in your table as observation 5. Also write the values
of both the charges and their masses.
11. Without changing the settings for Charge 2 and with the same value of Charge 2 in step 10, change the
distance between the charges by using the right pointing arrows of Charge 2 so that the angle θ is different
from all previous observations. Measure the new distance r and the angle θ and record it in your table as
observation 6. Also write the values of both the charges and their masses.
Grade 10 Coulomb’s Law Lab
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12. Using your observations, plot a graph between F and tan θ. The graph must have the correct labels for the
title, axes, and units. You can plot it by hand on a graph paper, take a picture and paste it here. You could also
use Microsoft Excel to generate the graph and paste that chart here.
3,5
3
2,5
2
1,5
1
0,5
0
0,5
0,4
0,3
0,2
0,1
0
*10^-4 N Electrostatic Force
Electrostatic Force
Tanθ
13. Draw the line of best fit and write the equation of the line of best fit. You can also use Microsoft Excel to do
that.
Grade 10 Coulomb’s Law Lab
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14. Calculate the slope of the line of best-fit (please provide units).
Slope = 7.6*10^-4
Equation of the graph=7.6*10^-4x-0.002998*10^-4
15. What physical quantity is represented by the slope of the graph? Explain using laws of physics and equations
why the slope of the line of best fit is the physical quantity you named. (Hint: draw a free body Diagram for
pith ball 2)
The physical quantity represented by the slope is weight of charge 2.
When ball 2 is affected by electrostatic force, weight, and tension. This gives us,
Fe = mgtanθ
Weight of charge 2 = (7.3*10^-5)*9.8 = 7.15*10^-4 N
16. Calculate the percentage error in the value of the physical quantity identified in step 15.
Percentages error=
=
=
(7.6 ∗ 10−4 ) − (7.15 ∗ 10^ − 4)
= 6%
(7.15 ∗ 10^ − 4)
Grade 10 Coulomb’s Law Lab
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