Two identical capacitors A and B , charged to the same potential 5 V are connected in two different circuits…

Two identical capacitors A and B, charged to the same potential 5V are connected in two different circuits as shown below at time t=0. If the charge on capacitors A and B at time t=CR is QA and QB respectively, then (Here e is the base of natural logarithm)

  1. QA=VCe,QB=CV2
  2. QA=VC,QB=CV
  3. QA=VC,QB=VCe
  4. QA=CV2,QB=VCe

Solution

Charge on capacitor after charging with a battery of potential VQ=CV

Now, capacitor A is connected as shown in the figure.

As diode is in reverse bias, so capacitor charge remains same after time t=CR.

 QA=CV

In case B, capacitor is connected as shown in the figure.

Here, diode is in forward bias, so capacitor discharges and its charge decays as 

QB=Q·e-tRC

where, t=RC

Asked in: JEE Main 2020 (09 Jan Shift 2)

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