# maths

Given the the instantaneous voltage across a capacitor is VC=40(1-e -t/CR) Volts When being charged by a 40 volt DC supply, find the time, t for VC to reach 18 volts after the charging process has started if C = 100ìF and R = 20kÙ

1. 👍 0
2. 👎 0
3. 👁 112
1. R = 20K Ohms.
C = 100uF.

R*C = 20*10^3 * 100*10^-6 = 2000*10^-3=
2 s.

E/e^(t/RC) = E-Vc.
40/e^(t/2) = 40-18 = 22
e^(t/2) = 40/22 = 1.8182.
t/2*lne = ln1.8182
(t/2)*1 = 0.59785
t = 1.2 s.

1. 👍 0
2. 👎 0
posted by Henry

## Similar Questions

1. ### Physics

A series RCL circuit contains only a capacitor (C=6.60 F), an inductor (L=7.20 mH), and a generator (peak voltage=32.0 V, frequency=1.50x10^3 Hz). When t  0 s, the instantaneous value of the voltage is zero, and it rises to a

asked by Anonymous on March 25, 2014
2. ### Physics

What value of voltage will be reached across the plates of a capacitor, after two time constants, if the maximum value of voltage when fully charged, reaches 200 volts?

asked by Jacob on June 10, 2013
3. ### physics

Consider a circuit with an input voltage, a resistor, and a capacitor,Imagine that the input voltage initially has size 12 volts at t = 0. At t = 10 it drops down to a value of 5 volts, which it then maintains indefinitely.Setting

asked by tendeukai on September 2, 2015
4. ### physics

Consider a circuit with an input voltage, a resistor, and a capacitor, as shown in • Imagine that the input voltage initially has size 12 volts at t = 0. At t = 10 it drops down to a value of 5 volts, which it then maintains

asked by tendeukai on September 2, 2015
5. ### Math (Confused, no idea where to begin)

The voltage V across a charged capacitor is given by V(t) = 2e^-0.16t volts, where t is in seconds (A) what is the voltage V(5) after 5 seconds? Find the time t when the voltage will be 1 volt Enter your answers to two decimal

asked by Picard on October 3, 2014
6. ### Physics

suppose you want to design a capacitor that uses mica as the dielectric material which has K = 7 and a dielectric strength of 150 MV/m. It is intended to store at least 1.- J of energy and be able to withstand a voltage up to 250

asked by Heidi on September 16, 2015
7. ### Physics

suppose you want to design a capacitor that uses mica as the dielectric material which has K = 7 and a dielectric strength of 150 MV/m. It is intended to store at least 1.- J of energy and be able to withstand a voltage up to 250

asked by Heidi on September 16, 2015
8. ### Physics Help!

A 220 uF capacitor with a 10% tolerance rating is charged. The voltage across the capacitor is measured to be 110 +/- 5.5 volt. Calculate the electrical charge stored in the capacitor. Estimate the error in the charge by

asked by Mary on January 27, 2012
9. ### physics

Having trouble with this one: A capacitor having a capacitance of 10uF is charged by 100v battery. A.)Calculate the charge on the capacitor? B.)calculate the energy stored in the capacitor? C.) the terminals of the capacitor is

asked by morgan on February 28, 2010
10. ### physics

Capacitor A has a capacitance CA =29.4 uF and us initially charged to a voltage of V1= 10.70 V. Capacitor B is initially uncharged . When the switches are closed, connecting the two capacitors, the voltage on capacitor A drops to

asked by Jp on November 23, 2011

More Similar Questions