# AC circuits

Discussion in 'Homework Help' started by xx123321, Apr 27, 2011.

1. ### xx123321 Thread Starter New Member

Apr 27, 2011
15
0
Hi guys, I am a freshmen of learning about AC circuits.
I got a question about the form of ac current.

Giving an ac current as follow,
i=100sin(314,15t)
what does above mean?I don't understand the meaning of comma between 314 and 15t

In addition,which 's the answer of the peak to peak of i? 200sin(314,15t) or just write down 200A?

2. ### Georacer Moderator

Nov 25, 2009
5,142
1,266
It's the european (metric) notation of decimal numbers. "." is the thousand marker and "," is the decimal spot in this side of the Atlantic. So in essense your sine is $i=100\cdot \sin(100\cdot \pi \cdot t)$

The peak to peak current (or voltage in other applications) is a constant number, and thus the answer is 200A. It expresses the "width", if you may, of the sine signal under examination.
Peak to peak amplitude can be defined in other waveforms too (triangular, square, etc).

3. ### xx123321 Thread Starter New Member

Apr 27, 2011
15
0
first,thanks for your help.
more one question,how about i=100sin(314,28t) ? The answer is also i=100sin(100pit),if yes,why?

4. ### Georacer Moderator

Nov 25, 2009
5,142
1,266
3.1415 is a valid truncation of pi at the fourth decimal place. 4.1428 is not. If it 's a result of numerous sequential operations and you know that this is the result you want, it's ok. But otherwise, two numbers can be equal or not. Period.

5. ### BillO Well-Known Member

Nov 24, 2008
985
136
In addition to what Georacer said, it depends on your margin of error and the resulting precision. If your precision is 3 significant digits them 314,15 and 314,28 are the same within that precision. In other words, they are both just 314. If however the situation demands 5 significant digits, then no, 314,28 is not a reasonable representation ∏.