Werry
Methods
3.1 Christopher Flip Coil Method
Method was followed directly from the lab instructions. The magnet was moved across the flip coil quickly and
consistently. The integrator circuit allowed for the measurement of voltage values, which were then used to
calculate the magnetic field value.
3.2 Current Balance Technique
The following construction was used to measure 4 different mass values for each of 4 different hairpins (SF37,
SF38, SF39, SF42). Matlab was used in order to plot the data and create a curve fit. All other methods were
followed from lab instructions.
Data/Calculations
3.1 Flip Coil Method
# turns = 2000 r = 1.9 +/- 0.1cm
B at block = 550 +/- 50 gauss C = 0.998 +/- 0.001F
0.1k
A = pi*r2 = 1.13 x10-3 m2 +/- 0.02 x10-3 m2
V
trial
(volts)
1
0.796
2
0.815
3
0.786
4
0.747
5
0.801
6
0.776
7
0.791
8
0.801
9
0.801
10
0.811
ave
0.7925
std. dev
0.01962
uncertaint 0.00620
y
4
0.000685T
B = 355 +/- 7 Gauss
R = 101.6 +/-
Comparison to accepted value:
This is not an acceptable t-value (>>1)
This percent error is also rather large.
3.2 Current Balance Technique
Hairpin
Length
(+/0.01cm)
SF37
2.20 cm
SF38
4.19 cm
SF39
3.19 cm
SF42
4.21 cm
Current
(+/0.01A)
4.62
5.14
6.14
7.15
4.61
5.14
6.14
7.12
4.62
5.14
6.17
7.13
4.62
5.11
6.15
7.08
Mass
(+/0.01g)
0.08
0.09
0.11
0.12
0.14
0.17
0.19
0.23
0.11
0.12
0.16
0.17
0.29
0.32
0.38
0.44
F=mg
(+/0.00001N
)
0.00078
0.00088
0.00108
0.00118
0.00137
0.00167
0.00186
0.00226
0.00108
0.00118
0.00157
0.00167
0.00284
0.00314
0.00373
0.00432
I*L
(+/0.01A*m
)
0.10
0.11
0.14
0.16
0.19
0.22
0.26
0.30
0.15
0.16
0.20
0.23
0.39
0.43
0.52
0.60
B = F/(IL)
(+/0.001T)
0.0077
0.0078
0.0080
0.0075
0.0071
0.0077
0.0072
0.0076
0.0073
0.0072
0.0080
0.0073
0.0073
0.0073
0.0072
0.0072
Analysis
2.1 Flip Coil Method
Q: Assume that the flip time is approximately 50ms. Choose a capacitor from the following: 0.001, 0.01, 0.1
and 1.0F. What is an appropriate choice for the resistance accordance R?
In with equation 13 :
For accurate integration, the time constant RC must be much greater than t. Choosing capacitor of 1.0F means:
Thus, an appropriate choice for R might be 200k, or anything much greater than 50k
2.2 Current Balance Technique
Q: Solve for B in Equation 19. What is the propagated error for the magnetic field, B?
Equation 19:
3.1 Flip Coil Method
Q: If you have taken the following measurements of the peak voltage from the oscilloscope, what are the
average, standard deviation and the standard deviation of the mean?
Measurements: 0.10, 0.12, 0.11, 0.13, 0.14, 0.10, 0.09 and 0.08 mV
3.2 Current Balance Technique
Q: What is the slope of the curve which you are asked to produce below?
Q: Discuss the results of both methods of determining magnetic fields. Which one do you find more reliable?
Why?
I find the current balance technique to be a more accurate method of determining the magnetic field. The flip
coil method involves more sources of systematic error: Resistance, Capacitance, measured Area, and Voltage.
The Voltage is dependent on the actual flip coil technique, which requires consistent movement of the magnet
and thus introduces more error.
Conclusion
The flip coil technique involved many sources for error. In addition to the systematic sources of error
mentioned above, the values for voltage varied with the speed that the user moved the magnet across the coil. A
larger source of error present here is in the determination of the area. The diameter or radius is measured by a
ruler that only has 2 significant figures and a high chance of human error (misreading, hand movements), and
then in order to determine area this uncertain value is then squared, increasing the error even more. For the
Current Balance method, special sources for error include the reading of the current value on the ammeter and
the inaccurate mass measurement device allowing for only 1 significant figure on a few values.