PHYS 233
35: Microwaves
Experiment #35
Microwave Optics
References
1. Instruction and Experiments Manual for the PASCO Microwave Optics System
(DOWNLOAD AND READ BEFORE DOING THE EXPERIMENT)
2. P.A. Tipler, Physics for Scientists and Engineers, 3rd ed., Worth (1991)
3. F.A. Jenkins and H.E.White, Fundamentals of Optics, 3rd ed., McGraw-Hill (1957)
4. C. Kittel, Introduction to Solid State Physics, any edition
Introduction
The term microwaves is used to describe electromagnetic radiation with wavelengths in
the range of approximately 1 metre to 1 millimetre. Microwaves provide a convenient way
to study the properties of electromagnetic waves because it is easy to build and handle
equipment that is comparable in size to the wavelength. In this experiment you will use
radiation with a wavelength of 2.9 cm to investigate some phenomena which should be
familiar from your study of optics. A brief introduction to the experiments is presented
here. The details of the microwave system and the experiments you will perform are given
in the PASCO manual. You should READ manual the week before you do the experiment
and study it carefully. The manual describes 13 experiments of which you are required to
complete the five experiments listed below and you may complete additional experiments
as an optional part of the lab or for an extended experiment. Follow the experimental
procedure and answer the questions in the manual. Record your data in your notebook,
NOT in the PASCO manual. Note that experiment 1 in the manual is an introduction to the
operation of the system and it is recommended that you work through it before starting on
the principal experiments. You should not feel constrained by the format of the PASCO
manual to do only the measurements suggested. Try to think of other measurements that
will illuminate the question being investigated.
Prelab Questions
The PASCO experiment manual contains questions pertaining to the experiments. Answer
those questions that don’t require you to have completed the experiment.
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PHYS 233
35: Microwaves
Apparatus
The equipment used in this experiment is described on pages 1 through 5 of the PASCO
manual.
Caution
• The output power of the Microwave Transmitter is well within standard safety levels.
Nevertheless, one should never look directly into the microwave horn at close range
when the Transmitter is on.
• Under some circumstances, microwaves can interfere with electronic medical devices. If you use a pacemaker, or other electronic medical device, check with your
doctor or the manufacturer to be certain that low power microwaves at a frequency
of 10.525 GHz will not interfere with its operation.
• Always mount the apparatus on a CLEAN, SMOOTH table. Before setting up the
equipment, brush off any material — particularly metal chips — that might have
adhered to the magnetic strips on the bottom of the Goniometer arms.
Experiment
1. PASCO Experiment 2: Reflection
2. PASCO Experiment 5: Polarization
In this experiment you will investigate the effect of metal slits on the polarization of
microwaves. In addition to the measurements in the PASCO manual in which the
effect on the transmitted microwaves is studied, you should also look at the effect on
the reflected microwaves (if any).
3. PASCO Experiment 12: Brewster’s Angle
4. PASCO Experiment 10: The Michelson Interferometer
5. PASCO Experiment 13: Bragg Diffraction
X-rays are used in the study of crystal structures because the wavelength of x-rays
is comparable to the spacing between atoms in a crystal. The crystal behaves as a 3dimensional diffraction grating. An analogous experiment is performed here in which
atoms are simulated by ball bearings held in a regular array in a foam block. The problem
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PHYS 233
35: Microwaves
is to determine the spacing between planes of “atoms” (ball bearings) from the wavelength
of the microwaves and the angular distribution of microwave intensity after the microwaves
have travelled through the block. The diffraction of microwaves by the ball bearing array
(or X-rays by a crystal) is described by Bragg’s Law:
nλ = 2d sin θ
where λ is the wavelength, n is an integer, d is the spacing between the planes of balls
(atoms) and θ is the angle between the incident beam of microwaves and the planes being
considered. The idea behind Bragg’s Law is that the path length for rays “reflected” from
successive planes should differ by an integral number of wavelengths. Constructive interference will then occur and a maximum in intensity will be observed. An edge-on view of
the “crystal” is shown below illustrating Bragg’s Law for (100) planes and n = 1. Kittel
(reference 4) provides a discussion of Bragg’s Law.
UG2/1993, NA/2012
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