# Voltage across capacitor

## Homework Statement

Voltage across 0.2-F cap is given by

v(t)=4(1-Є^(-10t)) for t>0

determine expression for the current i(t)

## Homework Equations

i(t)=c (dv(t))/dt

## The Attempt at a Solution

I'm really not sure were to begin with this problem what is the Є symbol and how do you take the derivative of it?

Mapes
Homework Helper
Gold Member
pmontone, you're in luck. That's not a Є symbol, but rather the constant e (= 2.718), the basis for the exponential function.

## Homework Statement

Voltage across 0.2-F cap is given by

v(t)=4(1-Є^(-10t)) for t>0

determine expression for the current i(t)

## Homework Equations

i(t)=c (dv(t))/dt

## The Attempt at a Solution

I'm really not sure were to begin with this problem what is the Є symbol and how do you take the derivative of it?

First, look at your given equation v(t) and try to understand its meaning. What happens to v(t) as t increases? Is this equation representative of a "charging" or "discharging" capacitor? Now, based on this answer, how do you expect the current across the capacitor to behave over time? Use your equation and then analyze the result for physical accuracy. Remember that a fully-charged capacitor acts as an open circuit (no current).