Parallel RC Circuits: Charging to 0.75V in Seconds

[erisedk]

Homework Statement

A parallel combination of 0.1M Ω resistor and a 10 μF capacitor is connected across a 1.5 V source of negligible resistance. The time (in seconds) required for the capacitor to get charged upto 0.75 V is approximately

(A) ∞
(B) ln 2
(C) log 2
(D) Zero

Homework Equations

$V = V_0(1-e^{\frac{-t}{RC}})$

The Attempt at a Solution

So, V₀ should be 1.5 V, and C is 10 μF. However, should't the voltage across the capacitor be 1.5 V at all times because it's in parallel with the resistance? Even if I use Thevenin's theorem, I get the resistance across the capacitor as 0 ⇒ time constant is 0. Please help?

 

[gneill]

If the 1.5 V source has negligible resistance then your Thevenin idea is correct and the circuit's time constant will be correspondingly negligible (effectively zero seconds). So how long will it take to fully charge the capacitor from 0 V to 1.5 V?

 

[erisedk]

Zero, so that should be the answer.

 

[gneill]

Yup.

 

[erisedk]

Thanks!