Absolute value of Sine Wave

[Basra123]

What is the period of the absolute value of
sin(120.pi.t)?

 

[charlie b]

Re: Absolute value of Sine Wave

1/120 second. Why?

 

[rattus]

Re: Absolute value of Sine Wave

Charlie, you must not have had your caffeine!

The period is 1/60 sec. Think about it.

 

[ron]

Re: Absolute value of Sine Wave

If the period of sin (t) is 2pi seconds (because every 2pi units of time t the function takes the same value, i.e. it takes 2pi units of time to complete a cycle), then the sin (120pi x t) has a period of 2pi/120pi which equals 1/60 second.

I'll admit cheating and looking at a reference book.

[ February 19, 2006, 10:32 PM: Message edited by: ron ]

 

[steve66]

Re: Absolute value of Sine Wave

I only have a few seconds to think about this, but isn't the period of Sin (120 pi t) = 1/60 sec?

Then isn't the period of |sin (120 pi t)| twice that? That would make it 1/120 sec.

Steve

 

[rattus]

Re: Absolute value of Sine Wave

Simply put,

2*pi*f*t = 120*pi*t
2*f = 120
f = 60
T = 1/60

or,

2*pi*f*T = 120*pi*T = 2*pi
T = 2*pi/(120*pi) = 1/60

 

[Basra123]

Re: Absolute value of Sine Wave

Steve,

I agree with your answer. I think the key here is that this is the absolute value of a sine wave and not the actual sine wave. This is like a rectified sine wave with a period of 1/120 rather 1/60.

 

[steve66]

Re: Absolute value of Sine Wave

One atta-boy for Charlie.

Did you see the absolute value Rattus?

Steve

 

[rattus]

Re: Absolute value of Sine Wave

Originally posted by steve66:
One atta-boy for Charlie.

Did you see the absolute value Rattus?

Steve

I see it now. Never heard a full wave rectified sine wave described that way though.

If it were a half wave rectified sine wave, the period would be 1/60.

 

[charlie b]

Re: Absolute value of Sine Wave

I saw it as a math question, not an electrical engineering question. That is why I did not question the manner in which the question was presented. But I still would like to know the reason for the question.

 

[Basra123]

Re: Absolute value of Sine Wave

Charlie,

This was a tricky question that I had encountered. Now I can see that the reason for the question is to account for the effect of the absolute sign on the period. I along with others forgot or missed this sign and didn't account for it and came up with 1/60 as opposed to 1/120 that you correctly calculated. It is mathematical question but it is also an engineering one since it represents a full wave rectification of the sine wave. if you plot it you will see a rectified full wave.