# 50 Hz waveform

Discussion in 'Homework Help' started by liam, Apr 27, 2008.

1. ### liam Thread Starter New Member

Apr 22, 2008
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could any one help us with this i have no idea where to start Find the instantaneous value of a 50 Hz waveform with a maximum value of 200v. 0.001 sec after it has passed through a voltage zero. many thanks . liam

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
v=Asin(2πft)
where v is the instantaneous voltage
A is the peak (maximum) voltage
f is the frequency
t is the time

so v=200sin(2πx50x0.001) =1.097 Volts

You said when it has passed through zero: so it may be positive like + 1.098 or negative like - 1.097

3. ### silvrstring Active Member

Mar 27, 2008
159
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Shouldn't this be done using radians? v(.001) would then be (+/-)61.8V.

4. ### mik3 Senior Member

Feb 4, 2008
4,846
63
No, he said 0.001 seconds not radians

5. ### silvrstring Active Member

Mar 27, 2008
159
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Yes, I know .001 is time, but omega(2pif) is in radians.

6. ### mik3 Senior Member

Feb 4, 2008
4,846
63
no its in radians per second and time is in seconds so id you multiply them you get radians

7. ### silvrstring Active Member

Mar 27, 2008
159
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Right. So you get 200sin(pi/10), or 200sin(18degrees). Both are 61.8V, right? Am I doing something wrong?

8. ### Caveman Active Member

Apr 15, 2008
471
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The dimensional analysis is:

t in seconds.
f = cycles/sec.

So, take the sine in radians. The 61.8 magnitude is correct.

9. ### hgmjr Moderator

Jan 28, 2005
9,030
214
I got 61.8 as well.

hgmjr

Mar 27, 2008
159
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Ok. Thanks.

11. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Oh yes you are right i forgot to make radians in degrees thanks for the correction. Stupid i am !!

12. ### liam Thread Starter New Member

Apr 22, 2008
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Thanks for the replies guys. but im still none the wiser as were you got the answer from . i understand that the answer is 61.8v. but where did this come from . when i tried working out the equation v=200sin(2πx50x0.001) =1.097 Volts i got - 0.107 ????

13. ### Caveman Active Member

Apr 15, 2008
471
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Okay, step by step
1. 2*PI radians/cycle * 50 cycles/second * 0.001 seconds = 0.314 radians

This is just stating that 0.001 seconds into a 50Hz sine wave is 0.314 radians in.

2. Take the sine of this, but remember to set up your calculator to calculate your trigonometric functions in radians. So, sin(0.314 radians) = 0.309

Just so you understand, what this says is that at 0.001 seconds into a 50Hz sine wave, the voltage is 0.309 times the peak.

3. Multiply by the peak voltage, 200V. 200V*0.309 = 61.8V.

Got it?

14. ### liam Thread Starter New Member

Apr 22, 2008
9
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your a absolute star! thanks for the really easy explanation. ive managed to work it out