# Science talk:Math Exam Resources/Courses/MATH152/April 2016/Question A 26

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Thread title | Replies | Last modified |
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Answer updated- please check the signs | 0 | 22:01, 26 March 2018 |

Hint and Solution Unclear | 2 | 21:57, 26 March 2018 |

Hi everyone,

I am pretty sure I got the signs right in this answer. The point is that a current pointing in the direction of i_1 will reduce the voltage V_1, because the current takes the positive charge away from the capacitor. A current pointing in the direction of i_2 will increase the voltage V_2 for the same reason.

Finally, Lenz's law states that a potential difference in an inductor induces a current pointing in the opposite direction, so dI/dt should point in the opposite direction of the potential difference.

-Rob

Hi Aili,

Perhaps it would help students if you did the following. Cite the names of the laws that you stated in your hint (if such equations have any), and justify how you obtained that system of equations in your solution (for instance, mention that you are applying your hint to the system of linear equations given in the question).

Best,

Brian

Hey Brian,

Thanks for your message.

I wrote my hint and solution based on the lecture notes http://www.math.ubc.ca/~elyse/152/2018/13LCR.pdf Unfortunately, I do not know the names of these differential equations. There are no names stated in the lecture notes as well. I am not an expert on this kind of circuit questions, so feel free to help me make any corrections or add more details to the solution.

Thanks. Aili

I don't like these notes because I thought that a "voltage drop" was the negative of the difference in voltage, and they seem to be using the opposite convention.