# Phase Shifts

Discussion in 'Homework Help' started by extremeads1, Feb 17, 2007.

Feb 10, 2007
64
0
Hello,
I have been taught and seen that there is a lead of current in a capacitor by 90degrees and lag of current in a inductor by 90 degrees.
What is the reason behind the phase shifts in these components !
pls do let me know fast..........

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Read the E-book on this site - Volume 2, chapters 3 & 4.

3. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
Essentially its because the current-voltage relationship for capacitors and inductors is of a variable that is dependant on a rate of change of an instantaneous value in the other variable, i.e. for a capacitor i = C(dv/dt) and for an inductor v = L(di/dt); where the derivative expression is the rate of change of an instantaneous value in the other variable.

For an explanation of the situation for a capacitor see: Volume II - Chapter 4.2

For an explanation of the situation for an inductor see: Volume II - Chapter 3.2

Dave

4. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
That and the following little nuggets
Code ( (Unknown Language)):
1.
2. d(sin(x))/dx = cos(x)
3.
4. d(cos(x))/dx = -sin(x)
5.
6. so cos(x) = sin(x-90degrees)
7.
8. and -sin(x) = cos(x+90degrees)
9.
Curious how things unfold