11 Analyse the PD Across a Charging and Discharging Capacitor

Question 1

what must always be checked when using an electrolytic capacitor in a circuit

Answer 1

it is a polarised component and so must be connected with the correct polarity. if connected incorrectly it could overheat and explode

Question 2

what graph can be plotted to confirm that the change in potential difference across a capacitor as it discharges is exponential

Answer 2

a graph of ln(V/Vo) against t. expected to form a straight line

Question 3

when plotting the discharge graph of ln(V/Vo) against t, how can the capacitors time constant be calculated.

Answer 3

-1/gradient

Question 4

what are the advantages of doing a trial discharge before carrying out the full experiment

Answer 4

a trial with your chosen values of R and C allow for suitable time intervals to be chosen depending on the speed of discharge

Question 4

equation of pd as capacitor charges

Answer 4

V=Vo(1-e^-t/RC)

Question 5

how can the time constant be found using an oscilloscope and a stopwatch

Answer 5

use the lap function to time when voltage falls to predetermined values on the oscilloscope. this can then be plotted on a graph