Calculating Voltage Decay in a Resistor-Capacitor Circuit

AI Thread Summary
To calculate the time for the voltage to fall to 10^6/D of its original value in a resistor-capacitor circuit with a 35 microfarad capacitor and a 120-ohm resistor, the time constant T is determined using T = cR, which equals 4.2 milliseconds. The final voltage can be expressed as V(final) = V(initial) e^(-t/T), and logarithms may be necessary to solve for time. In a separate circuit with a switch, capacitor, and bulb, the bulb will initially remain off as the capacitor charges, then gradually brighten as the capacitor reaches its maximum charge. This behavior reflects the charging process of the capacitor over time. Understanding these principles is essential for analyzing RC circuits effectively.
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If a charged capacitor c=35 micro farads is connected to a resistor R=120 ohms how much time will elapse until the voltage falls to 10^6/D of its original max value?

Ciruit contains a switch, resistor, emf and a capacitor in series.

Relevant equations are Time constant= T=cR and V(Final)=V(initial) e^-t/cr


I think it requires logarithms but i am not sure.

Can you please help me how to answer this.
 
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Another question is:

A circuit containing a switch, Vo, a capacitor and a bulb in series.

The capacior is originally uncharged. Describe the behaviour of the bulb from the instant the switch is on until a long time later.

I think there will be a delay for the bulb to emit light and then it will emit light getting slowly brighter as the capacitor is getting charged up.

Is this right?
 

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