Catherine Connors 35162393

Propagation of Electromagnetic Waves on a Line (Lab 7)

Introduction

The purpose of this lab is to study the behavior of standing electromagnetic waves on parallel wires using a transmission line and a frequency generator.

In the short-circuited Lecher line part of the experiment, one would expect the current nodes to be located at λ/4, 3 λ/4, and 5 λ/4. One would expect the voltage nodes to be located at 0, 2λ/4, 4λ/4, and 6 λ/4. In the open-ended Lecher line part of the experiment, one would expect the current nodes to be located at 0 , 2 λ/4, 4 λ/4, and 6 λ/4. One would expect the voltage nodes to be located at λ/4, 3 λ/4, and 5 λ/4.

The light bulb probes in this experiment measure the behavior of the electric and magnetic field lines. When the lamp on an electric field probe goes completely dark, that indicates that the voltage has reached zero, indicating a node. This works the same way for the magnetic field probes and the current intensity.

Procedure

1. Plug in the UHF (ultra-high frequency generator)2. Place the bridging plug at the end of the Lecher line3. Move the magnetic field probe along the Lecher line (this is the one with the

induction loop, not the one that is applied immediately to the transmission lines.)4. Record the positions at which the lamp on the probe does not emit light.5. Remove the induction loop and attach the lamp to the electric field probe, which

is applied directly to the transmission lines.6. Move the electric field probe along the Lecher line7. Record the positions at which the lamp on the probe does not emit light8. Remove the bridging plug from the end of the Lecher line9. Move the magnetic field probe along the Lecher line10. Record the positions at which the lamp on the probe does not emit light11. Remove the induction loop and attach the lamp to the electric field probe12. Move the electric field probe along the Lecher line13. Record the positions at which the lamp on the probe does not emit light.

Data and Results

IV-1a:x i=27cmx f=32cmn=1

IV-1b:x i=10.5cmx f=13cm

n=2

IV-2a:x i=8.7cmx f=18.5cmn=2

IV-2b:x i=28.5cmx f=31.2cmn=3

0.5 1 1.5 2 2.5 3 3.50

5

10

15

20

25

30

35

f(x) = 9.43055555555556 xR² = 0.768047136108639

Series2Linear (Series2)

n

x (c

m)

S=9.4306σ S=0.663

S= λ4

λ=4 S=4 (9.4306 )=37.7

v=fλ=(433.9MHz ) (37.7cm )=1.64∗108ms

Conclusions

The experimental results do not match the theory very well. The calculated nodes do not seem to be where the nodes hypothetically should be.

The primary source of error was the fact that the lights in the room were bright enough to make locating the point where the lamp was not emitting any light very challenging.

Questions

Q-1:

σ λ=4 σ S=4 (0.663 )=2.7 cm

Q-2:

σ v=f σ λ=433.9 (0.027 )=11.7MHz