# Help with sketching the current graph

Discussion in 'Homework Help' started by ENG99, Sep 1, 2014.

1. ### ENG99 Thread Starter Member

Feb 13, 2014
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Hello there, I have hard time sketching this graph and I don't know if my answer is correct or not, the question in the attachment + my answer please help me out

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2. ### shteii01 AAC Fanatic!

Feb 19, 2010
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515
What is the formula for current in terms of charge?

Feb 13, 2014
37
0
I=dq/dt

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
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How many time intervals do you have?

5. ### ENG99 Thread Starter Member

Feb 13, 2014
37
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At t=2s and t=6s

6. ### shteii01 AAC Fanatic!

Feb 19, 2010
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There are three.
Interval 1: 0<=t<=2
Interval 2: 2<=t<=6
Interval 3: 6<=t<=8

You got Interval 1 and Interval 3 right.

What is your equation of q for Interval 2?

7. ### ENG99 Thread Starter Member

Feb 13, 2014
37
0
(y2-y1)/(x2-x1)

8. ### shteii01 AAC Fanatic!

Feb 19, 2010
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That looks like formula for slope. You got -8.33 for slope? Is that what you are trying to say?

9. ### ENG99 Thread Starter Member

Feb 13, 2014
37
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No I got -8.33 from I=C/t => I=-50/6 =>-8.33

10. ### shteii01 AAC Fanatic!

Feb 19, 2010
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That looks like bull shit.
C is unit of charge, Coulomb, named in honor of Charles-Augustin de Coulomb.
So you got some nonesence and you divide that nonesense by some time that you picked, and you got some number. That aint gonna work bro.

What is the equation of q in the interval 2<=t<=6?

11. ### Jony130 AAC Fanatic!

Feb 17, 2009
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Charge in the interval 2s to 6s ramps down -100C per 4s. So in one second the charge ramps down in rate equal to ?

12. ### ENG99 Thread Starter Member

Feb 13, 2014
37
0

q = integral (i)t dt

13. ### shteii01 AAC Fanatic!

Feb 19, 2010
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I think I am done here. Good luck.

Feb 13, 2014
37
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25 ?

15. ### Jony130 AAC Fanatic!

Feb 17, 2009
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1,117
well -25. But do you finally understand how you can find dq/dt ?