Hi,
I have read the topic on inductors,my understanding so far is as following.
a) Current carring straight wire's megnetic flux:
On a current carring straight wire of any conductive material, megnetic flux builds up,
How much flux build up, it depends on the amount of current and cunductivity of the wire material.Even when i bend the wire, flux remains there.
so this flux is because of self induction ?
please help me understanding these terms in detail, becouse i got confused
a) self induction
b) mutual induction
c) induction
tks
Sid
Hi there,
Self induction or rather self inductance is the measure of something's ability to produce an effect of inductance. That's probably the easiest way to understand this. It happens because something produces a current that is opposite to the original current that was the source of activation in the first place, and that something is called inductance.
Inductance is the phenomenon where a changing magnetic field causes (induces) an electric current to flow in a wire. Self inductance occurs when a changing magnetic field caused by a current in turn causes another current to flow in the opposite direction and so partly cancels out the original current. Currents add algebraically, so the total current would be the original minus the self induced current. We dont actually measure these two currents individually however, we only measure the total current.
So we have induction, which is a change in magnetic field producing a current in a wire, and self induction where a change in current produces a change in magnetic field which in turn produces another current in the opposite direction and so cancels out some of the original current which reduces the total current flow at that point in time. An inductor exhibits this behavior so we measure the inductance and this is what is called the self inductance. It's in units of Henries.
Mutual inductance is almost the same, except there are two or more wires or coils that are close enough together so that their magnetic fields influence each other. Current in one coil affects its magnetic field which in turn affects the magnetic field around the second coil which in turn affects the current in the second coil. So we have overall the current in the first coil affecting the current in the second coil. The amount of mutual inductance depends on a lot of factors like the distance between the two coils. Coils that are close together are said to be tightly coupled, and may have a coupling factor as high as 0.99 for example, where 1.00 is perfect coupling and 0.00 is no coupling at all.
There are a couple of equations if you would like to try to work out some examples. The first and simplest one for inductance is:
V=L*di/dt
where
V is the voltage across the coil,
di is the change in current through the coil,
dt is the change in time between points we are looking at, and
L is the self inductance we talked about above.
The above is sometimes estimated by calling di and dt "delta i" and "delta t" where these two are relatively small changes in the variables i and t.
For example, we might look at this equation at two points in time at t=10.0us and t=10.1us, so dt=0.1us here, and measure current levels i=1.000 amps and i=1.001 amps, where di would be 0.001 amps here. Knowing the self inductance L for that coil, we could then calculate V.