, having a simple and convenient waveform, namely, the sine wave. Such a sine wave is illustrated in Figure A.17. Any sine wave can be characterized by its frequency, phase, and amplitude. These were introduced in Section 2.3.3, and much of that information is repeated here for direct continuity. Note in the figure that half a cycle of the sine wave is designated by IT and a full cycle by 2. Remember that there are 2 radians in a circle or 360 degrees, and 1 IT radian is 180 degrees. Therefore 1 radian is 180°/IT or 57.29582791 That is an unwieldy number and is not exact. That is why we like to stick to using IT, and the value is exact. In Figure A.17 the maximum amplitude is +A and -A; the common notation for wavelength is i. To convert wavelength to frequency and vice versa we use the formula given in Section 2.3.3, or = 3 X 108 m/sec. (A.26) Figure A.17 A typical sine wave showing amplitude and wavelength. 6'In this text, unless otherwise specified, logarithms are to the base ten. These are called common logarithms. Under certain circumstances we will also use logarithms to the base 2 (binary system of notation). In the calculus, nearly all logarithms used are to the natural or Naperian base. This is named in honor of a Scottsman named Napier. However, Napier did not use the base E but used a base approximately equal to e-1. REVIEW OF FUNDAMENTALS OF ELECTRICITY WITH TELECOMMUNICATION APPLICATIONS We recognize the constant on the right-hand side of the equation as an accepted estimate of the velocity of light (or a radio wave). The period of a sine wave is the length of time it takes to execute 1 cycle (1 Hz). We then relate frequency, F, to period, T, with: F=1/T, (A.27) where F is in Hz and T is in seconds. Voltage and current may be out of phase one with the other. The voltage may lead the current or lag the current depending on circuit characteristics, as we will see. When an ac circuit is resistive-there is negligible capacitance and inductance-the voltage and current in the circuit will be in-phase. Figu