A sine wave has a maximum value of 560 V. At what angle of rotation will the voltage reach a value of 123 V?

Answer 1

560 = 560 * sin(90) (where it is at it's maximum value)
123 = 560 * sin(a)

123/560 = sin(a)
0.2196 = sin(a)
a = 12.7 degrees (use the inverse-sine function on your calculator)

The voltage will also be 123 volts at 180 - 12.7 = 167.3 degrees.

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