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# Alternating current graph help?

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1. Hey guys i'm not really sure how to draw the graph

A current i(t) = 10cos(200πt) flows through a 100Ω resistance. Sketch i(t) andthe power p(t) to scale versus time. Find the average power delivered to theresistance.

For the power i just i drew two humps that are max at 10KW, they start from -2.5ms and then rise to the max at 0s at 10kW and then back down to 0 at 2.5ms then rises back up to max at 5ms and goes back to 0 at 7.5ms. So i didn't draw it like a proper cosine graph because it is squared and not sure if this is correct. With the current i drew it with the first half similar as it rises to max current at 10A and then goes down to -10A at 5ms where the power would be at max again in opposite phase, so the graph and two waves look out of phase and quite dodgy.
2. (Original post by ErniePicks)
Hey guys i'm not really sure how to draw the graph

A current i(t) = 10cos(200πt) flows through a 100Ω resistance. Sketch i(t) andthe power p(t) to scale versus time. Find the average power delivered to theresistance.

For the power i just i drew two humps that are max at 10KW, they start from -2.5ms and then rise to the max at 0s at 10kW and then back down to 0 at 2.5ms then rises back up to max at 5ms and goes back to 0 at 7.5ms. So i didn't draw it like a proper cosine graph because it is squared and not sure if this is correct. With the current i drew it with the first half similar as it rises to max current at 10A and then goes down to -10A at 5ms where the power would be at max again in opposite phase, so the graph and two waves look out of phase and quite dodgy.
The power curve should be >= 0 and double the frequency of the current curve. it doesn't seem like you've done anything wrong.
3. (Original post by Joinedup)
The power curve should be >= 0 and double the frequency of the current curve. it doesn't seem like you've done anything wrong.
Thank you, but just to be clear it is still a cosine graph and not a sin graph right?
4. (Original post by ErniePicks)
Thank you, but just to be clear it is still a cosine graph and not a sin graph right?

well it's a cos^2(x) graph really, doesn't cross y=0
does have a maximum at x=0 though

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