# plz help !!!!circuits

#### kitibwa

Joined Apr 10, 2008
3
see attachment

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#### Caveman

Joined Apr 15, 2008
471
What's the deal? You have time for four exclamation marks, but not to type the details to your question? Type it out for cripes sake!

#### Dave

Joined Nov 17, 2003
6,970
Can you scan the question and upload it as an attachment?

Dave

#### mik3

Joined Feb 4, 2008
4,843
For all t0SummaryV(t) = { 10cos(2t), t 0}Find and sketch i(t) for t>0Hint: try sketching using microsoft excel.
It is just the graph of a cosine with t>0 but with double the frequency of an ordinary cosine graph. Also to amplitude is not from 1 to -1 but from 10 to -10.

#### Caveman

Joined Apr 15, 2008
471
That's what I thought, but then I noticed that he defined V(t), but asked for i(t).

#### mik3

Joined Feb 4, 2008
4,843
That's what I thought, but then I noticed that he defined V(t), but asked for i(t).
If the voltage is applied on a resistor, the current (i(t)) will have the phase as the voltage but divided by the resistors value.

If the voltage is applied to an inductor the current will lag the voltage waveform by 90 degrees, thus it will be a sine wave. Also divide by the reactance to find its amplitude.

If the voltage is applied to a capacitor the current will lead the voltage by 90 degrees, thus it will be a sinewave. Also divide by the reactance to find its amplitude.