Hi, for number 18 what topic should I study for this? I have reviewed electricity etc. but have not seen such anywhere? Is this related to motors and generators?
P.S: Are time constants on the exam alot?
Hi Jacob, that’s a good question. I think that possibly it may have been a mistake by the examiners to set question 18: if you look at the examiners’ report for 2011 it refers to a part of one question that was off the syllabus. However, transformers could at a pinch be considered to be part of the ‘electromagnets’ topic, so it’s maybe worth having a quick read of a basic tutorial on transformers like http://www.learnabout-electronics.org/ac_theory/transformers01.php.
By time constants, you mean RC circuits? If so, it is worth being familiar with how the capacitor law Q = VC, and Ohm’s law V = R dQ/dt lead to the differential charge/discharge equation Q = (-) RC dQ/dt, and how to solve this to get an exponential decay.
do you have any source for the derivation of the exponential decay?
Hi Rickardo, you can check out the derivation here: http://web.mit.edu/sahughes/www/8.022/lec09.pdf or a quick google search of ‘exponential decay of charge derivation’ can get you some other websites 🙂
Thanks for that link Jess. Looks good.
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