Register to reply

Conservation of charge, but not conservation of energy

by imsickofweed
Tags: charge, conservation, energy
Share this thread:
Nov19-09, 12:58 PM
P: 1
1. The problem statement, all variables and given/known data

A DC voltage (V) in series with a resistor of value R and in series with a capacitor (C1) at time t=0 a switch closes to put another capacitor (C2) in parallel with C1 and in series with V and R. The charge on C1 at t=0- Q1(0-)=/0 (doesn't equal 0) and charge on C2 at t=0- Q2(0-)=0 at time t=0+ C2 begins to charge and eventually comes to equilibrium. Show conservation of charge exists and that conservation of energy doesn't exist

2. Relevant equations

energy lost = power x time = ∫I(t)2 R dt

I(t) = \frac{V_1\,-\,V_0}{R}\,e^{-\frac{1}{CR}\,t}

V_1\ -\ V(t) = (V_1\,-\,V_0)\,e^{-\frac{1}{CR}\,t}

Energy lost (to heat in the resistor):

\int\,I^2(t)\,R\,dt\ =\ \frac{1}{2}\,C (V_1\,-\,V_0)^2[/itex]

Efficiency (energy lost per total energy):

[tex]\frac{V_1^2\,-\,V_0^2}{V_1^2\,-\,V_0^2\,+\,(V_1\,-\,V_0)^2}\ =\ \frac{1}{2}\,\left(1\,+\,\frac{V_0}{V_1}\right)

3. The attempt at a solution

I'm just not sure how to set up the equations to show that it works.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
Phys.Org News Partner Science news on
Physical constant is constant even in strong gravitational fields
Montreal VR headset team turns to crowdfunding for Totem
Researchers study vital 'on/off switches' that control when bacteria turn deadly

Register to reply

Related Discussions
Conservation of momentum vs conservation of kinetic energy Introductory Physics Homework 18
Kirchhoff's First Rule - Electrical Charge / Energy Conservation Classical Physics 2
Simulatenous Conservation of Momentum and Conservation of Energy Engineering Systems & Design 9
Conservation of energy or conservation of momentum Introductory Physics Homework 2
Conservation of momentum (with conservation of energy) Introductory Physics Homework 1