Here’s your task: given a capacitor of unknown capacitance, determine the capaci

Question

Here’s your task: given a capacitor of unknown capacitance, determine the capacitance by charging and then discharging the capacitor. A few words of caution: first, do not charge a capacitor to potentials differences greater than they are intended to withstand. Second, discharge your capacitors between every trial. Lastly, do not touch the terminals of a charged capacitor: the resulting shock can be harmful to you and damaging to the capacitor.

These rather large capacitors take a non-negligible amount of time to charge and discharge. Start by connecting one of the “unknown” capacitors to a resistor in series. The resistor is both for safety and to slow down the charging and discharging process. Connect the voltmeter across the capacitors terminals, turn on the power supply, and observe the increase in potential.

Question 1: What are we doing to the capacitor?

Question 2: Can you say anything about the charge on the capacitor’s terminals?

Question 3: What about the energy stored in the capacitor?

Question 4: Where is the work coming from to enact this process?

Once fully charged, quickly disconnect the power supply from the loop and close the circuit measure while measuring voltage across the capacitor as a function of time.

Question 5: Why does the potential decrease?

Explanation / Answer

Q1: when connecting to the battery, we're charging the capacitor

Q2: they are the same, but of opposite signs

Q3: increases until the maximum charge the capacitor can acquire: W=CU2/2

U=potential difference between the plates

C=capacitance

Q4: from the battery

Q5: the capacitor discharge through the resistor; this means its energy goes to the resistor.

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