PAG 9.1 Investigating Charging and Discharging Capacitors Flashcards
What must always be checked when using an electrolytic capacitor in a circuit?
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
State the equation for time constant for 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
Also how long it takes to discharge to 37% of full capacity
What device is used to measure the potential difference across a capacitor and how should it be connected
Voltmeter in parralel across ends of capacitor
What graph can be plotted to confirm the exponential decay of a capacitor’s potential difference as it discharges?
Graph of ln(V/Vo) against t
Straight line graph
When plotting a discharge graph of ln(V/Vo) against t, how can time constant be obtained?
(-)gradient
What is the benefit of doing a trial discharge before carrying out the experiment in full?
Allows you to choose suitable time intervals to take recordings at, depending how quickly capacitor discharged with values R and C
What is the maximum voltage that you should use in this experiment?
Capacitors have voltage ratings - do not exceed this
How can the time constant of a discharging capacitor be measured using an oscilloscope and stop-clock?
Lap function on stop-clock to record the times that the voltage falls to predetermined values on oscilloscope.
Data plotted on graph to determine time constant
What is the advantage of using the lap function rather than writing down the time at each voltage interval
Avoid you having to look between screens
May result in lower uncertainty
What measuring device could be used to measure the resistance of an unknown resistor?
Multimeter or ohmmeter
How can you determine the length of your error bars for time?
Picking the mid-range time measurements and calculating the range of the repeat readings at that time
Range as error bar length
