1. Electrical energy that has escaped into free space exists in the form of electromagnetic waves. These waves, which are commonly called radio waves, travel with the velocity of light and consist of magnetic and electrostatic fields at right angles to each other and also at right angles to the direction of travel.
2. One half of the electrical energy contained in the wave exists in the form of electrostatic energy, while the remaining half is in the form of magnetic energy.
3. The essential properties of a radio wave are the frequency, intensity, direction of travel, and plane of polarization. The radio waves produced by an alternating current will vary in intensity with the frequency of the current and will therefore be alternately positive and negative.
4. The distance occupied by one complete cycle of such an alternating wave is equal to the velocity of the wave divided by the number of cycles that are sent out each second and is called the wave length.
5. The relation between wave length X in meters and frequency in cycles per second is therefore
The quantity 300 000 000 is the velocity of light in meters per second. The frequency is ordinary expressed in kilocycles, abbreviated KC; or in megacycles, abbreviated MC. A low-frequency wave has a long wave length while a high frequency corresponds to a short wave length.
6. The strength of a radio wave is measured in terms of the voltage stress produced in space by the electrostatic field of the wave and is usually expressed in microvolts stress per meter.
7. A plane parallel to the mutually perpendicular lines of electrostatic and electromagnetic flux is called the wave front.
8. The wave always travels in a direction at right angles to the wave front, but whether it goes forward or backward depends upon the relative direction of the lines of electromagnetic or electrostatic flux.
9. If the direction of either the magnetic or electrostatic flux is reversed, the direction of travel is reversed; but reversing both sets of flux has no effect.
10. The direction of the electrostatic lines of flux is called the direction of polarization of the wave. If the electrostatic flux lines are vertical the wave is vertically polarized; when the electrostatic flux lines are horizontal and the electromagnetic flux lines are vertical, the wave is horizontally polarized.
III. After-text Exercises:
1. Agree or disagree with the next statements:
1. Radio waves consist of magnetic and electrostatic fields at right angles to each other and also at right angles to the direction of travel.
2. The radio waves produced by alternating current will not vary in intensity with the frequency of the current and will not therefore be alternately positive and negative:
3. The distance occupied by one complete cycle of such an alternating wave is equal to the velocity of the wave divided by the number of cycles that are sent out each second and is called the wave length.
4. The quantity 200 000 000 is the velocity of light in meters per second.
5. The frequency is ordinary expressed in kilocycles or in megacycles.
2. Find the information about:
1) the velocity of radio waves;
2) the form of existence of the electrical energy in the wave;
3) the essential properties of a radio wave;
4) the relation between wave length in meters and frequency in cycles per second;
5) the expression of frequency.