1-7
Q-8. What is the mathematical formula for computing the output voltage from a moving coil in a
magnetic field?
AMPLITUDE
A sine wave is used to represent values of electrical current or voltage. The greater its height, the
greater the value it represents. As you have studied, a sine wave alternately rises above and then falls
below the reference line. That part above the line represents a positive value and is referred to as a
POSITIVE ALTERNATION. That part of the cycle below the line has a negative value and is referred to
as a NEGATIVE ALTERNATION. The maximum value, above or below the reference line, is called the
PEAK AMPLITUDE. The value at any given point along the reference line is called the
INSTANTANEOUS AMPLITUDE.
PHASE
PHASE or PHASE ANGLE indicates how much of a cycle has been completed at any given instant.
This merely describes the angle that exists between the starting point of the vector and its position at that
instant. The number of degrees of vector rotation and the number of degrees of the resultant sine wave
that have been completed will be the same. For example, at time position 2 of figure 1-3, the vector has
rotated to 60 degrees and 60 degrees of the resultant sine wave has been completed. Therefore, both are
said to have an instantaneous phase angle of 60 degrees.
FREQUENCY
The rate at which the vector rotates determines the FREQUENCY of the sine wave that is generated;
that is, the faster the vector rotates, the more cycles completed in a given time period. The basic time
period used is 1 second. If a vector completes one revolution per 1 second, the resultant sine wave has a
frequency 1 cycle per second (1 hertz). If the rate of rotation is increased to 1,000 revolutions per second,
the frequency of the sine wave generated will be 1,000 cycles per second (1 kilohertz).
PERIOD
Another term that is important in the discussion of a sine wave is its duration, or PERIOD. The
period of a cycle is the elapsed time from the beginning of a cycle to its completion. If the vector shown
in figure 1-3 were to make 1 revolution per second, each cycle of the resultant sine wave would have a
period of 1 second. If it were rotating at a speed of 1,000 revolutions per second, each revolution would
require 1/1,000 of a second and the period of the resultant sine wave would be 1/1,000 of a second. This
illustrates that the period is related to the frequency. As the number of cycles completed in 1 second
increases, the period of each cycle will decrease proportionally. This relationship is shown in the
following formulas:
