Question,help with sinusoidal voltage

Thread Starter

Sahilp

Joined May 21, 2020
3
A sinusoidal voltage has a value of 80 V at 2.4 ms and it takes time of 20 ms to complete one cycle. Determine the maximum value and time to reach it for the first time after zero
 

ci139

Joined Jul 11, 2016
1,463
if you are an electrical engineer your AC is RMS . . . if you are a physicist your AC is peak amplitude . . . considering how the question is asked you likely are an EE
 

Thread Starter

Sahilp

Joined May 21, 2020
3
if you are an electrical engineer your AC is RMS . . . if you are a physicist your AC is peak amplitude . . . considering how the question is asked you likely are an EE
Sorry I didn't get it. Can you please solve my question in a paper
 

WBahn

Joined Mar 31, 2012
25,760
Sorry I didn't get it. Can you please solve my question in a paper
No, we cannot solve your question in a paper. This is YOUR homework and this is NOT the Homework Done For You forum.

You need to show YOUR best attempt to solve YOUR homework problems. We will then help you get past specific spots where you are getting stuck.
 

MrAl

Joined Jun 17, 2014
7,592
A sinusoidal voltage has a value of 80 V at 2.4 ms and it takes time of 20 ms to complete one cycle. Determine the maximum value and time to reach it for the first time after zero
Some hints:
1. You know the frequency from the cycle time of 20ms.
2. I see you know the form of the function is f(t)=Vm*sin(2*pi*f*t).
3. Using the frequency you find from #1 insert that into the function.
4. Equate the resulting function to the voltage you know 80v and the time you know 2.4ms when it reaches 80v.
5. Now the only thing you dont know is Vm, so solve for that.

This is a basic method for solving a lot of different problems. Form an expression, then insert all of the known data and see if you can solve for any unknown variables that are left.
 

WBahn

Joined Mar 31, 2012
25,760
there's nothing told about the phase shift in the task description - if one is involved - you can't find anything
That was my first thought when I saw the OP. The TS may be expected to assume that it is a sine (as opposed to a cosine) wave with zero phase shift).

We'll probably never know since it appears that the TS has gone elsewhere to find someone to do their homework for them.
 

ci139

Joined Jul 11, 2016
1,463
TS has gone elsewhere to find someone to do their homework for them.
shame , that today's computerized education leaves the kids impression that all must(/can) be done fast . . . even learning the new stuff . . . no any persistence . . .

. . . it's just missing some lessons at the beginning guiding people what and with what expense (time, skills) can be done with computers . . . and what is much faster done without . . . with the pen and paper
 

MrAl

Joined Jun 17, 2014
7,592
as in fact - i never considered such as option - that until you proposed it
i was thinking they thought the 80V is the amplitude value at 2.4ms and they ask for RMS of it . . . funny
Hi,

Well yes, and when they state an amplitude value and a time value they usually refer to the actual waveform not some derived unit or measure, but that is an interesting question about RMS vs Peak values.
So for me the question to be answered is what is Vm in this:
80=Vm*sin(2*pi*(1/0.020)*0.0024)
and then solve for Vm.
I think the TS took a hike anyway though.
 

WBahn

Joined Mar 31, 2012
25,760
as in fact - i never considered such as option - that until you proposed it
i was thinking they thought the 80V is the amplitude value at 2.4ms and they ask for RMS of it . . . funny
The explicitly asked for the maximum value, not the RMS value.

In order to come up with an answer based on the information given, we have to make some assumptions, namely that it is a sine wave with no phase shift. We don't really have to assume that it has zero DC offset because that is strongly implied by stating that the voltage is sinusoidal.

We don't have to assume anything about what is meant by the 80 V because they state that that is the voltage of the waveform at a specific time. So we have

80 V = Vm * sin(2π·(2.4 ms / 20 ms))

Of course the time to reach the first max after zero is determined by the assumption of the waveform and we don't need to know what Vm is in order to find the time.
 
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