Revision of Circuits and Electronics Part 1 - Lumped Circuit Abstraction (lecture 1)

Suppose we wish to answer a question like-
What is the current through a bulb?


 We could do it the hard way  with Maxwell's equations or the easy  way where certain conditions are ignored. So to do it the easy way, replace the bulb with a discrete resistor and use Ohm's law to find the current. The discrete resistor becomes the lumped element abstraction of the bulb.

From Maxwell's equations, a problem arises where  the rate of change of charge w.r.t. time may not be equal to zero when finding the current.

(1) To be unstuck from this problem, we have to make it equal to zero!

(2) The voltage also needs to be defined and for this, rate of change of flux  w.r.t. time outside the element is equal to zero.

(3)Signal speeds should be less than the speed of light.

The above is not really true in general but  is the playground for EECS.


KVL- sum of voltages in loop is zero
KCL- sum of currents in node is zero



Video:-
http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/video-lectures/lecture-1/



Lecture notes:-  http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/lecture-notes/