Equipment: Microwave Optics Kit: Transmitter, Receiver, Meter-stick Introduction

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Light Speed and Malus’ Law Name__________________
Equipment:

Microwave Optics Kit: Transmitter, Receiver, Meter-stick

Introduction:
Confined waves of any type can exhibit standing wave features. This means that we can find time-stable locations where maximums and minimums in wave amplitude will exist. These locations are called Anti-Nodes (A) and Nodes (N), anti-node meaning maximum displacement, and node meaning no displacement.
In this lab a microwave transmitter will directly face a receiver. The transmitted wave will proceed directly toward the receiver and then reflect back to the transmitter. The process repeats multiple times, and any location where waves interfere purely constructively will be (A), whereas any location where waves interfere purely destructively will be (N).
Suppose that the transmitter and receiver are separated by a distance d and the receiver is reading a maximum in amplitude (A). If the receiver is moved a distance of

further away from the transmitter, the reflected waves will have to travel exactly one wavelength more in distance and will thus exactly repeat the previous standing wave conditions with every (A) repeating. Furthermore, the receiver will be at a new (A) condition.
What you will see as you slowly move the receiver away will be a reduction in the receiver reading followed by a return to nearly the same maximum value it had before being moved. When it is back to maximum, we know the receiver has moved a distance of

.
The best experimental value will be obtained by measuring several multiples of this distance. You will first find and record an (A) condition. Next you will smoothly and slowly move the receiver away from the transmitter watching as the reading goes to minimum (N) and then back to (A), counting the number of times this happens.
Procedure – For all parts record your data in your lecture or lab notebook.
Part 1 Speed of Light Experiment

Record the transmitting frequency of the microwave transmitter.
Orient the transmitter and receiver so that an (A) can be read clearly on the receiver scale.
Align a meter stick along the side of the transmitter and receiver.
Note the position of the receiver. Slowly pull the receiver away from the transmitter, counting the number of antinodes, until you have counted 15 antinodes. Record the new position of the receiver at the 15^th antinode.

Part 2 Malus’ Law

Position the source and receiver so they are directly facing one another and about 20 cm gap between horns. Both source and receiver should be aligned at 0 degrees.
Turn on the source and receiver and adjust the variable sensitivity so that a signal of about 0.5 is on the meter. Slowly slide the receiver backward until a relative maximum in signal intensity is observed. Re-adjust the sensitivity until a reading of 1.0 is achieved.
Rotate the receiver to 10 degrees. Record the signal level.
Repeat step 3 for 20, 30, 40, 50, 60, 70, 80, and 90 degrees.

Part 3 Exploring Microwaves

Position the source and receiver so they are directly facing one another and about 30 cm gap between horns. Both source and receiver should be aligned at 0 degrees. Adjust the distance and sensitivity until a reading of 1.0 is on the scale. Determine the # of sheets of paper required to reduce the reading to 0.75, 0.50, and 0.25.
Now point the transmitter and receiver along perpendicular lines. Note the configuration a metal plate must be at in order to reflect a maximum amount of microwave radiation into the receiver.

Summing Up

Part 1 Speed of Light Experiment

Use your data to determine the wavelength of the microwaves. Explain your method in complete sentences.

Compute your experimental value for the speed of light by multiplying the transmitting frequency by the wavelength you determined above.

Part 2 Malus’ Law

Make a graph with the y-axis containing two values, the measured signal strength and cos², versus the x-axis which is the angle . Attach this graph to the report. Your graph should have a legend identify your y-values correctly and the axes should be labeled correctly.

Part 3 Exploring Microwaves

How did the transmitted microwave intensity depend on the thickness of paper?

Diagram the situation which produced the maximum reading in the transmitter due to reflection.

CYP Labs