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I have this circuit

enter image description here

My task is to match these four statements.

  1. "\$v_1=0\$ for a very long time. The time constant for the charging time for the capacitor immediately after \$v_1\$ jumps to \$v_1=10V\$ is ...

  2. "\$v_1=10V\$ for a very long time. The time constant for the discharge time for the capacitor immediately after \$v_1\$ jumps to \$v_1=0\$ is ...

  3. \$R_2\cdot C\$

  4. \$(R_1+R_2)\cdot C\$

I can't really find any arguments as to why these statements belong together.

Has it something to do with the diodes not being forward biased? I hope someone can clarify this for me.

Edit

The main problem I have with this, is that I don't exactly understand how the capacitor is charging and discharging through the resistors, and when and why the diodes are conducting and non-conducting.

I just saw the answers to this problem. For number 1 they have this drawing.

enter image description here

For number 2 they have this drawing.

enter image description here

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  • \$\begingroup\$ You should match "question" 1 with "answer" 3 or "answer" 4 and "question" 2 with the remaining "answer" (answer 3 or answer 4) \$\endgroup\$ – Huisman Dec 11 '19 at 14:02
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    \$\begingroup\$ Has it something to do with the diodes not being forward biased? So all the diodes are in reverse mode? Are you sure? Consider the cases where C has no charge and V1 is 1) a negative voltage 2) V1 = 0 V and 3) When V1 = a positive voltage. \$\endgroup\$ – Bimpelrekkie Dec 11 '19 at 14:03
  • \$\begingroup\$ Huisman, can you please explain why this is? \$\endgroup\$ – Carl Dec 11 '19 at 14:04
  • \$\begingroup\$ There are other relations as well: All four statements relate to each other because they all address the same circuit. Statement 3 and 4 relate because the only consist of component value variables. But assuming this is a homework assignment, I think my first comment makes most sense. \$\endgroup\$ – Huisman Dec 11 '19 at 14:56
  • \$\begingroup\$ Do you understand that V1 either changes from 0V to 10V, or from 10V to 0V, and you have to align these two conditions with the time constants given in 3. and 4.? \$\endgroup\$ – Chu Dec 11 '19 at 14:57
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A diode is only conducting when its anode side has a higher voltage than its cathode side.

So you can think of it as a one-way street for current, where current can only flow in the direction of the arrow symbol of the diode.

This is why you have two different current paths for charging and decharging of the capacitor and thus two different time constants.

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