Instructables

Step 8: What does a capacitor do in a circuit?

Picture of What does a capacitor do in a circuit?
Lesson Objectives:
  • Investigate what a capacitor does in a circuit.
  • Investigate how a capacitor is constructed.
Materials: mini incandescent bulbs, bulb sockets, batteries, battery cases, connecting wires, compass, 0.025 F capacitor, 0.1 F capacitor, stopwatch, dissected capacitor

Capacitors have positive and negative ends and must be connected to the battery in the correct orientation to operate properly. Each capacitor specifies the maximum electric potential difference (voltage) that can be safely connected to the capacitor, please do not exceed this limit. The negative lead of the capacitor is labeled, this end is connected to the positive end of the battery.

Design and complete an investigation to determine what a capacitor does in a circuit. An important piece of evidence for these investigations is the time it takes to charge and discharge the capacitor. Begin your investigation by connecting these two circuits:
  • Connect three D cell batteries, two mini incandescent bulbs, and the capacitor all in series and use the compass to observe what is happening with charge flow once the batteries are connected.
  • Once the charge flow has stopped, disconnect the batteries but leave the rest of the circuit intact. Connect the two wires that were connected to the battery to each other and use the compass to observe what is happening with charge flow.

As you continue your investigation, explore circuits with different numbers of batteries in the charging circuit, bulbs of different resistances, bulbs in parallel with the capacitor, and borrow a capacitor from another lab group to explore capacitors in series and in parallel with another when the capacitors are identical and when they are different.

Lab Questions
1.  Are the bulbs lit longer when charging the 0.025 F capacitor or the 0.1 F capacitor through the same circuit? Why do you think this happens?
2.  Does the charge that flows into the capacitor during charging get used up in the capacitor? Or does it get stored somewhere in the capacitor?  How do you know?
3.  Is the same thing happening in every wire during charging?  Is the same thing happening in every wire during discharging?  What is the evidence?
4.  Where do you think the charge comes from that lights each of the bulbs during capacitor charging?
5.  Where do you think the charge comes from that lights each of the bulbs during discharging?
6. When two identical capacitors are connected in series to each other, do they store more or less charge than they do individually? What about in parallel? What is your evidence?
7. When two different capacitors are connected in series to each other, do they store more or less charge than they do individually? What about in parallel? What is your evidence?
 
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