RC Circuits

This java applet shows the transient behavior that occurs when a capacitor is charged and discharged in a RC circuit.

1. You will find a 10 Volt Voltage source, Click within the green area and drag the mouse up/down to change its value.

2. A 100k ohms resistor and a 100uF in series。（ k=103 , u=10-6 ). There is a switch to control the flow path of the circuit.

3. Click near the (Black) switch to change between horizontal position: charging and vertical position: discharging.

If you click the mouse button twice, the timing record t will be reset to zero. You can get a plot of V_c vs t similar to this (click me).

4. Press Start to start the animation, The program will show the voltage across the capacitor(Vc) and resistor.It also draws the Vc vs t(ime) curve.

5. You can change the switch at any time.

6. If the mouse is inside the Vc-t plot area, Its values corresponse to mouse position will be displayed. If you drag the mouse, It will show relative value.

7. The animation is suspended when you press the mouse button. If you click with left mosue button, the animation continues when you release the mouse button. If you click with the right mouse button, you will need to press the mouse again to resume.

From Kirchoff's loop Rule

During the changing process: Vo = VR + Vc

= I R + ∫I dt/C

During the discharging process Vc = -VR

= ∫I dt/C = -I R

How to do the calculation?

If the time interval dt is very small,

integral become summation.

During the charging process:

1. Find current I => I = (Vo - Vc )/ R

2. Then calculate the new Vc => Vc = Vc + I *dt/C

3. calculate VR = I * R

You should be able to figure out the rest.

Your suggestions are highly appreciated. E-mail ： hwang@phy03.phy.ntnu.edu.tw

`Author：Fu-Kwun Hwang, Dept. of physics, National Taiwan Normal University`
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