# Physics 121A H04 Lab 223 Faraday Law

Physics 121A – H04

Introduction

Objectives

In this lab the voltage induced in a coil by a changing magnetic field will be measured and compared to the predicted value by Faraday’s Law.

Theory

Using Faraday’s Law, the theoretical value obtained will be compared to the experimental value obtained from the experiment.

Through a loop, the magnetic flux () is given by:

Since the function generator is set to sine, the current can be given as a function of time by I = Io*sin(wt). Thus: B(t) = B0*sin(wt) = (8.992x10-7)(N(h)I0/R)sin(wt)

Procedures

1. First, begin by setting up the (calibrated) Helmholtz coils, magnetic field sensor, detecting coil, multimeter and ammeter in series
2. Next, Calibrate the two Helmholtz coils in the same direction with the compass and DC power supply.
3. Make sure that the function generators and multimeters are reading correctly and properly connect all the pieces of the apparatus
4. Adjust the function generator to the first frequency and use the amplitude dial to ensure that the current remains at 30 amps.
5. Then, record the magnetic field and potential on the computer and record data from the graphs
6. Repeat steps 4 and 5 for the rest of the frequencies and record data
7. Compare theoretical and experimental values

Data & Result

 Helmholtz Current (mA) Frequency (Hz) B0 (mT) Theory EMF Exp EMF RMS voltage Peak RMS voltage 12.8 800 0.178707 0. 1.227798 0.874 1.23602 11.9 400 0.3387176 0. 1.130723 0.799 1.12996 11.5 200 0.526366 0. 0.904077 0.642 0.90792 10.6 100 0.674548 0. 0.559901 0.396 0.56003 9.8 50 0.731399 0. 0.303888 0.215 0.304056

Discussion

When we compared the theoretical values to the experimental ones, we observed that they were very similar. Our percent error had some outliers however they were not far off for each of the trials. Human errors and complications that may have occurred in the lab can explain the error that might have resulted. In the end we were still able to accurately observe and experiment with Faraday’s Law.

Conclusion

Throughout this lab we were able to gain a better understanding of Faraday’s laws through the experimental procedures. We were able to use those laws to calculate the voltage induced in a helmoltz coil. In the end we were able to accurately verify the law through doing the lab.

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