# Phase difference in CR and LR circuit

I have just done an experiment on CR and LR circuits.
http://img9.picsplace.to/img9/21/RC.jpg [Broken]

Connect channel 1 of the CRO across both the capacitor and resistor and channel 2 across the resistor.The trace on channel 1 is taken as the p.d. across the capacitor and that on channel 2 as ths current throught the capacitor.
http://img9.picsplace.to/img9/21/RL.jpg [Broken]

Replace the capacitor waith a high inductance coil fitted on a double C-core.

1.Why is channel 1 is connected across both the capacitor and resistor and not only the capacitor?

2.Why the trace on channel 2 gives the current through the capacitor?

3.When we increased the resistance value, the phase difference decreased.Why?

4.what is the phase difference between the p.d. and the current?

5.Change the resistance value and observe how this affects the phase
difference.Describle and explain the change,if any,in the phase difference.

6.Replace the capacitor with a high inductance coil fitted on a double c-core.Observe the CRO traces and note the phase diff between the p.d. across the inductor and the current through it.What is the phase diff. between the p.d. and the current?Why is it not 90°? How to sketch the CRO traces?

7.Change the resistance value and observe how this affects the phase difference.Describle and explain the change, if any, in the phase difference.

I have so many question to ask ..

Last edited by a moderator:

## Answers and Replies

Related Advanced Physics Homework Help News on Phys.org
berkeman
Mentor
Welcome to the PF, cash. It's a great resource for your learning. We have a rule here that you must show some of your own work in order for us to help you. We don't just give out answers to homework questions -- we try to help you to figure out the answers yourself.

So, to that end, I'll mention a couple things and ask a couple questions. First, you are connecting your oscilloscope so that you can see the voltage waveforms at the input to the circuit and the midpoint of the circuit. That lets you see the AC voltage waveform phase shift that results from going through the first component. Now, if you are monitoring the voltage across the bottom resistor with a 'scope probe, why does that tell you something about the current?

And tell us what you know so far about why there is a phase shift in LR and CR circuits. Have you seen the differential equations yet for the voltage-to-current relationship for a capacitor? For an inductor?