Calculating Voltage Across a Capacitor

In summary, the conversation discusses a circuit containing a capacitor and the equation for current as a function of time. The time constant of the circuit is determined to be 7 seconds and the initial current in the circuit is calculated to be 0.2A. However, when plugging in this value into the equation, the resulting voltage is incorrect, causing confusion. The question remains whether V=IR represents the voltage across a capacitor.
  • #1
roam
1,271
12

Homework Statement



[PLAIN]http://img189.imageshack.us/img189/4555/capacitorh.jpg


Homework Equations



[itex]I(t)=I_0 e^{-t/\tau}[/itex] (current as a function of time for a capacitor being charged)


The Attempt at a Solution



The time constant of the circuit is τ=RC=7s. And the initial current in the circuit is

v/Req=300/1489=0.2A (I know this is correct)

Now pluging into the equation:

[itex]I(5)=0.2 e^{-5/7}=0.0979 \ A[/itex]

[itex]V=IR= 0.0979 \ A \times 1489 \Omega = 145.73 \ V[/itex]

But the correct solution must be 153V. I'm very confused, what's wrong with my working? :confused:
 
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  • #2
Is V=IR the voltage across a capacitor? ehild
 

FAQ: Calculating Voltage Across a Capacitor

What is the definition of voltage across a capacitor?

Voltage across a capacitor is the difference in electric potential between the two plates of the capacitor. It is measured in volts and represents the amount of charge stored on the plates.

How is the voltage across a capacitor calculated?

The voltage across a capacitor can be calculated by dividing the charge on the plates by the capacitance of the capacitor. This can be represented by the equation V = Q/C, where V is the voltage, Q is the charge, and C is the capacitance.

What factors affect the voltage across a capacitor?

The voltage across a capacitor is affected by the amount of charge stored on the plates, the capacitance of the capacitor, and the type of material used for the plates. It is also affected by the frequency and amplitude of the applied AC voltage.

How does the voltage across a capacitor change over time?

When a capacitor is connected to a voltage source, the voltage across it increases until it reaches the same value as the source voltage. When the source is disconnected, the voltage across the capacitor decreases exponentially over time, with the time constant depending on the capacitance and resistance in the circuit.

What is the significance of the voltage across a capacitor in electronic circuits?

The voltage across a capacitor is an important aspect of electronic circuits as it determines the energy storage capacity of the capacitor. It also plays a role in filtering out AC signals and smoothing out the output of a power supply. The voltage across a capacitor is also used in various applications such as timing circuits and signal processing.

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