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I'm new to EE, and I am reading a text book which says:

Phase describes the position of the waveform relative to time 0.

The a quiz asks What is the phase shift for a sine wave with the maximum amplitude at time zero, the answer is 90 degrees.

I'm confused, why it is not 0 degree?

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    \$\begingroup\$ What is sin(0)? \$\endgroup\$
    – TimWescott
    Oct 10, 2019 at 23:25
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    \$\begingroup\$ You misunderstand the question. They are asking - "If you move the waveform along the axis so that it's maximum amplitude is at 0 degrees, how many degrees do you need to (phase) shift it?". Draw some pictures. A "normal sine wave" starts at V=0 at time 0 - so it certainly isn't at maximum value at time o, as you suggest. Now phase shift the wave until the peak is at 0 degrees. How many degrees did you have to move it? \$\endgroup\$
    – Russell McMahon ♦
    Oct 10, 2019 at 23:27
  • \$\begingroup\$ Does my answer make sense to you? \$\endgroup\$
    – Russell McMahon ♦
    Oct 11, 2019 at 5:36
  • \$\begingroup\$ @RussellMcMahon yes thanks, already accepted your answer \$\endgroup\$
    – secondimage
    Oct 11, 2019 at 11:30

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You misunderstand the question.
They are asking - "If you move the waveform along the axis so that it's maximum amplitude is at 0 degrees, how many degrees do you need to (phase) shift it?".

Draw some pictures.
A "normal sine wave" starts at V=0 at time = 0 - so it certainly isn't at maximum value at time 0, as you suggest.

Now (phase) shift the wave until the peak is at 0 degrees.
How many degrees did you have to move it?

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