# Phase Shifts

Joined Feb 10, 2007
64
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..........

#### beenthere

Joined Apr 20, 2004
15,819
Read the E-book on this site - Volume 2, chapters 3 & 4.

#### Dave

Joined Nov 17, 2003
6,970
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

#### Papabravo

Joined Feb 24, 2006
14,389
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
That and the following little nuggets
Rich (BB code):
d(sin(x))/dx = cos(x)

d(cos(x))/dx = -sin(x)

so cos(x) = sin(x-90degrees)

and -sin(x) = cos(x+90degrees)
Curious how things unfold