AP Physics 2‎ > ‎Unit 5‎ > ‎Current Flow‎ > ‎

RC Charging Lab

RC Charging Lab

Purpose:

The purpose of this lab is to look at the charging of a capacitor through a resistor.  

Info:

  • Lab Setup:


Procedure:

Part 1:  Qualitative

  1. Open up the program found here.

  2. Set your resistor to some value between 90 and 150 Ohms.  Put your capacitor at 50 µF and set the battery to 10 V.

  3. Throw the switch and watch all the values changing.  Discharge the capacitor if you need to watch it again.

  4. Answer these questions in your lab book.

  5. Q1:  What is the voltage across the capacitor immediately after the switch is thrown?

  6. Q2:  What is the voltage across the resistor immediately after the switch is thrown?

  7. Q3:  What happens to the voltage on the resistor as time progresses?

  8. Q4:  What happens to the voltage on the capacitor as time progresses?

  9. Q5:  What happens to the current as time progresses?

  10. Q6:  What happens to the charge on the capacitor when time progresses?

  11. Q7:  After a long time has progresses, what should be the voltage across the resistor?

  12. Q8:  After a long time has progresses, what should be the voltage across the capacitor?

  13. Q9:  After a long time has progresses, what should be the current in the circuit?

  14. Q10:  What is the final charge on the capacitor?

  15. Q11:  Why does the charge on the capacitor eventually stop changing?

  16. Keep everything else the same and change the voltage of the battery to 3 V.  Again watch the charging of the capacitor over a period of time.

  17. Q12:  Is the final charge on the capacitor larger, smaller or the same as it was when we used the 10 V battery?  Why?

  18. Return the battery to 10 V.  Lower the value of the capacitor to 5 µF.  Open the switch.  Discharge the capacitor.  Close the switch and observe the charging of this new capacitor.  

  19. Q13:  How is the charging of the smaller capacitor different than the charging of the big capacitor?

  20. Return the value of the capacitor to 50 µF.   Raise the resistance by a factor of 10. Open the switch.  Discharge the capacitor.  Close the switch and observe the charging of the original capacitor through a bigger resistor.

  21. Q14:  How does the charging of the capacitor change with a larger value of R?

Part 2:  Quantitative

  1. Put your capacitor at 50 µF and your resistor in the 1000 to 3000 Ω range.  Set your battery to 10 V.

  2. Create a data table with 10 rows of data that will track the time elapsed, the voltage across the resistor, the voltage across the capacitor, the charge of the capacitor, and the current in the circuit.

  3. Close your switch and reopen it almost immediately.  Record your first set of data.

  4. Repeat this procedure.  Try to open the switch each time the voltage on the resistor drops by 1 V.

  5. Make a graph of your each of your columns as functions of time.  Put your times in seconds, charge in C and current in A.

  6. Make a graph of your voltage on the resistor as a function of current.  What is your slope?

  7. Make a graph of your charge stored on your capacitor as a function of voltage across the capacitor.  What is your slope?

Part 3:  Live Part (Watching it Happen)

  1. Build a RC series circuit using the capacitor and resistor given to you by your teacher.  Include a battery and a switch to make your circuit just like the one we used virtually.

  2. Hook a voltage probe across the resistor in your circuit.

  3. Attach the voltage probe to channel 1 of the Lab Quest.

  4. Hook a second voltage probe across the terminals of your battery and attach it to channel 2 of your Lab Quest.

  5. Hook the Lab Quest to the USB port of one of the desktop computers in the room.

  6. Open Logger Pro

  7. Set the time of collection to 10 second and the number of points to 1000 samples per second.

  8. Don't set triggering.

  9. Start collecting data and throw your switch simultaneously. 

  10. Once you are done collecting data, create a new calculated column that will determine the voltage on the capacitor.

  11. Display all three graphs simultaneously.  Transfer this mass of graph into your lab book.

Stuff to have in your lab book:
  1. Purpose
  2. Picture of the lab setup
  3. Data Table
  4. Graph and equation
  5. Conclusion
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