Experiments with microwaves

Aim of the experiment

• To deepen the knowledge related to wave phenomena,
• To verify the relationships in wave physics experimentally,
• To model phenomena and devices in wave optics.

For the purpose:

• We summarize the basic knowledge on wave phenomena,
• We examine reflection, refraction, interference and diffraction of microwaves,
• We assemble some experimental setups (which are also useful in optics) based on interference of waves, and measure the wavelength of the used microwave.

Theoretical summary

In the experiment we use microwaves to study wave phenomena. Microwaves - as well as light - are electromagnetic waves of wavelength about 1 mm - 30 cm (correspondingly, the frequency of microwaves is $\setbox0\hbox{$ 10^{9} - 3 \cdot 10^{11}\ \text{Hz} $}% \message{//depth:\the\dp0//}% \box0%$).

Polarization of waves

In a transversal wave the vector related to the changing quantity is in the plane perpendicular to the direction of propagation but within this plane its direction is arbitrary. A certain direction of oscillation can be selected by putting a block in the path of the wave. This way behind the block a wave can be observed in which the oscillation takes place in the plane determined by the selected direction of the block and the direction of propagation. This type of wave is plane polarized wave, and the method is called polarization of waves. The selected plane is the plane of polarization, the block which creates the polarized wave is called polarizer, and usually for the selected direction direction of polarization is said. Different kind of waves can be polarized by using different methods: Transversal waves on a string or rope with a slit, electromagnetic waves with a mirror or with an equipment made of special material, microwaves with metal grating. Polarized waves have a characteristic property, namely they can be canceled out by using a polarizer of direction perpendicular to the plane of the oscillation. In case of electromagnetic waves the above definition of polarization is not unambiguous since in the plane perpendicular to the direction of propagation there are two vectors perpendicular to each other. By agreement in this case the plane of polarization is the plane containing the electric field vector.

Reflection and refraction of waves

Fig. 1: Reflection and refraction of waves (közeg means medium)

Waves propagate in finite sized medium, sooner or later they reach the boundary of the medium (for electromagnetic waves the madium can be vacuum). According to experience waves are partially reflected by the boundary, and partially refracted by the boundary, penetrating in the other medium generally by changing its direction of propagation. By using the notations of [#fig:1|Fig. 1]] laws of reflection and refraction are as follows: