By Ishaan Dhadral
LAB 4: Electric Charge
Purpose: to calculate the values and numbers of the charges of particles suspended between the two
charged plates by investigating/measuring their motion in an electric field, and the voltage required to
keep said particle suspended (net force = 0).
Table 1:
Droplet (#)
Terminal Velocity, Vt
(m/s)
Balancing Voltage VB
(V)
Mass, m (Kg)
(x10-17)
1
2
3
4
5
6
7
8
9
10
1.400±0.001
1.073±0.001
1.073±0.001
1.262±0.001
1.409±0.001
1.014±0.001
1.139±0.001
1.014±0.001
1.150±0.001
1.400±0.001
81.7± 0.1
14.4± 0.1
143.9± 0.1
28.4± 0.1
49.6± 0.1
32.2± 0.1
54.1± 0.1
21.4± 0.1
23.6± 0.1
245.0± 0.1
8.01±0.01
4.70±0.01
4.70±0.01
6.51±0.01
1.409±0.01
1.014±0.01
1.139±0.01
1.014±0.01
1.150±0.01
1.400±0.01
Determining Mass of drop:
Drop 1
m = (k)(Vt)2
m = (4.086E-17)(1.400)2
m = 8.01E-17 kg
Uncertainty:
= 1.400 ± 0.07%
= 1.4002 ± 0.14%
= (±0.14%)
= ± 0.01E-17 kg
By Ishaan Dhadral
Table 2:
Droplet (#)
1
2
3
4
5
6
7
8
9
10
Charge on droplet, q (C)
(x10-19)
4.81±0.01
16.0±0.1
1.60±0.01
11.24±0.06
8.02±0.03
6.40±0.03
4.81±0.02
9.63±0.06
11.2±0.07
1.603±0.003
Number of excess charges, n
+3.00±0.01
+10.00±0.06
+1.00±0.01
+7.02±0.04
+5.01±0.02
+3.99±0.02
+3.00±0.01
+6.01±0.04
+7.01±0.04
+1.001±0.002
Determining Charge on the droplets:
q = (Fg)(d)/(VB)
q = (8.01E-17 kg)(0.05 m)/(81.7 V)
q = 4.81E-19 C
Uncertainty
= (±0.14%)/(±0.12%)
= (±0.26%)
= 0.01E-19 C
Determining Excess Charges:
n = (4.81E-19)/(1.602E-19)
n = +3.00 ± 0.26%
n = +3.001 ± 0.01
Discussion:
The electric charges Always seem to be very close to integers. As we projected, the charges can be
calculated to show the number of extra charges.
By Ishaan Dhadral
Conclusion:
Our goal for this experiment was to investigate the motion of a particle between two charged plates, to
find the terminal velocity and to then calculate the charges on the different oil drops to see if we come
up with an integer for number of the number of excess charges(in the case of Oil drop #1 we had the
corresponding values: q = (4.81±0.01)E-19± C, n = +3.00±0.01). I successfully applied the oil drop theory
to the measured values to attain our goal. One disproportionate uncertainty was calculated, in the case
of Oil drop number 10, we see an unusually high voltage which can be the cause of the excessively small
uncertainty.