So I've been studying AC Circuits lately and I've come across a few things that I'm not able to digest. Let's take a pure inductive circuit for example.
This is the first time I'm experiencing current and voltage are not in sync with each other it's really weird why is the inductor doing that.
I mean If I think about think about certain points, there are some points where voltage is zero in the circuit zero voltage but we have current to be maximum. How does that make any sense
And then you have these points over here where the voltage is maximum in the circuit but the current is at zero. Just what is going on here?
Never experienced anything like this in previous circuits so I'm really really trying to figure out what's going on over here. Any help will be appreciated.
Best Answer
This is because in an inductor, current does not follow voltage version of Ohm's law.
Voltage and current are simply two very different things; voltage characterizes how much electric charges are separated, it is a measure of single-sign charge concentration and of its Coulomb electric field; while current characterizes how much the mobile charges are moving, it is a measure of electric charge flow. In general these two things could be totally unrelated, but in special cases they are related.
Ohm's law is intuitive and simple relation between voltage and current:
$$ I = U/R $$
valid in metals when current does not change in time too quickly. But you have to realize that in general, current does not require force to be causing it; current can simple be, just like moving asteroids move around the Sun without any force pushing them around. Current can just flow due to inertia. It can also be driven by other forces than the force of the Coulomb field (quantified by voltage in AC circuits). For example, it can be driven by chemical reactions (inside electrochemical cell or a battery of them) even against the voltage. Or it can be driven by induced electric field, which is a separate kind of electric field independent of the Coulomb field and thus independent of the voltage concept.
In the simplest case where ideal inductor is connected to harmonic AC voltage source, current is driven by both the AC voltage source, and also by the inductor's induced electric field. These two forces cancel each other so that finite current can exist in the circuit. This is because inside ideal inductor conducting body, electric field has to vanish, so voltage on the inductor is exactly minus induced EMF. This induced EMF is proportional to rate of change of current (Faraday's law). So when the current is changing the most, the induced EMF has the greatest magnitude. Consequently, voltage has the greatest magnitude as well. This happens when the current is zero.