RP09: Charging and discharging capacitors Flashcards
What must always be checked when using an electrolytic capacitor in a circuit?
The electrolytic capacitor is a polarised component and so must be connected with the correct polarity in the circuit. If connected incorrectly, it can overheat and become a safety hazard.
BOOM
What equation is used to calculate the time constant of a resistor capacitor circuit?
T = RC
What information does the time constant tell us?
How long it takes for the capacitor to charge to 63% of its full capacity as well as how long it takes for it to discharge to 37% of its full capacity.
What device is used to measure the potential difference across a capacitor and how should it be connected?
A voltmeter should be connected in parallel across the ends of the capacitor.
What equation shows how the potential difference across a capacitor varies with time as it discharges?
V=V0 e ^(-t/RC)
Where v0 is initial pd across capacitor.
What is the advantage of taking logarithms before plotting an exponential relationship?
Means that it is plotted as a straight line so the desired variables can more easily be obtained.
What graph can be plotted to confirm the exponential decay of a capacitor’s potential difference as it discharges?
A graph of ln (V/V0) against t can be plotted which should form straight line graph.
When plotting a discharge graph ln(V/V0) against t, how can the capacitor’s time constant be obtained?
The graph will have an equation@
ln(V) = ln(V0) -t/RC
So the time constant RC is given by -1/gradient
What is the benefit of doing a trial discharge before carrying out this experiment in full?
A trial discharge with your chosen values of R and C allows you to choose a suitable time interval to take recordings at depending on how quickly the capacitor discharges.
State the equation that shows how the potential difference across a capacitor varies with time as it charges.
V = V0 (1 - e^-t/RC)
Where V0 is the pd across the fully charged capacitor.
