# Find time constant

1. Apr 22, 2014

### utkarshakash

1. The problem statement, all variables and given/known data
The time constant of charging for the capacitor shown in the figure is

2. Relevant equations

See attached diagram

3. The attempt at a solution

$\tau = R_{eq} C$

$R_{eq} = R/2$

So the answer should be t= RC/2. But the correct answer is 0!

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2. Apr 22, 2014

### Staff: Mentor

Once the switch is closed all the components are in parallel, right? What's the rule for the potential across components in parallel?

3. Apr 22, 2014

### utkarshakash

They all have the same potential difference.

4. Apr 22, 2014

### Staff: Mentor

Right. And if the voltage source is ideal and the wires have entirely negligible resistance, then the capacitor voltage immediately after the switch closes must be....

5. Apr 22, 2014

### utkarshakash

It should be V. Thus time constant must be 0. Thanks !

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