Electronics SAC folio

[shokstar]

Hey guys, if you want to, it would be of great help if some of you could help me with some questions from my SAC folio i am having trouble with, and half of the physics students at my school are as well.

This first one is related to the capacitor prac of our folio. Why does the rate of charging decrease over time? and also what happens to the capacitor when the external voltage is put higher than the capacitor voltage?

Thanks for your help. More coming.

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Hey Shoka
 
the rate of the capacitor charging decreases over time beacause of the build up charge within the capacitor.

u should kno that a capacitor consists of two plates. When charge (electrons) flows within the circuit they build up on ONE of the plates within the capacitor.
This accumalation of charge on that plate gives that plate an overall NEGATIVE charge; this creates resistance to the flow of charge because of the effect of LIKE CHARGES REPELS.

Charge entering the capacitor towards the negative plate is repeled (which reduces current on one side of the capacitor)
and charge already within the capacitor ON THE OTHER PLATE is also repeled by the negative plate (thus the OTHER plate has an overall postive charge).
The overall positive charge on the OTHER plate also has an attraction to the negative charge flowing towards power supply (which in turn reduces current on the other side of the capacitor).

The effect of the postive plate and the negative plate increases over time, hence we can also say the rate at which charge flows within the circuit (i.e. current) decreases over time.   

Hence as the amount of charge on the plate increases,
-the resistance of the capacitor within the circuit increases due to build up of charge within the capacitor
-plates within the capacitor gain an overall negative or positive charge which increases over time
-this causes the rate at which charge flows in the circuit (i.e. current) into the capacitor to decrease over time. (directly translates to rate of a capacitor chraging decreasing over time)

hope this helps, and that i wasnt too confusing or too long winded

rashmi_34

[shokstar]

RASHMIII thanks man, that helped a lot. Also if you dont mind sharing how to explain the clipping in the transistor part 3 with relation to Vs and Vc, everyone I've asked has no idea.

thanks rashmi youre a legend

[rashmi_34]

NPS!!!!!!

Ask ashwin about the transistor stuff. We are both goin thru it but everytime i look at it it just gives me headaches,
So i let ashwin do all the work! He'll be happy to help you out.

Ps

to tidy up the answer by what i mean to the OTHER side is the side of the capacitor closer to the negative end/0v rail