# Ac through a resistor

My book says, that in a purely resistive AC circuit, the applied voltage has to overcome the DROP IN POTENTIAL across the resistance only. What does it mean? How will the voltage OVERCOME the potential drop?
Furthermore, it says that in a purely inductive AC circuit, the applied voltage has to overcome the back EMF only? Can you please explain this as well?
Original post by Imanxfaps
My book says, that in a purely resistive AC circuit, the applied voltage has to overcome the DROP IN POTENTIAL across the resistance only. What does it mean? How will the voltage OVERCOME the potential drop?

Original post by Imanxfaps
Furthermore, it says that in a purely inductive AC circuit, the applied voltage has to overcome the back EMF only? Can you please explain this as well?

You will need to give us the context for this question.

What example is the book using for the description?

As written and with no context, neither statement makes sense.
Original post by uberteknik
You will need to give us the context for this question.

What example is the book using for the description?

As written and with no context, neither statement makes sense.

The topic is " A.C through a resistor." The lines are: as a result of alternating voltage provided by the ac source, an alternating current will flow in the circuit. The applied voltage has to overcome the potential drop in the resistance only i.e, V= IR. And then they've derived the formula for alternating current through a resistor.
Original post by Imanxfaps
The topic is " A.C through a resistor." The lines are: as a result of alternating voltage provided by the ac source, an alternating current will flow in the circuit. The applied voltage has to overcome the potential drop in the resistance only i.e, V= IR. And then they've derived the formula for alternating current through a resistor.

It's very poorly worded, however, I believe the text is trying to lay the foundation for describing both current and voltage waveforms when applied to a) purely resistive circuits and following on b) reactive circuits with a mix of resistive, inductance and capacitance.

Of course, resistance is as described: resisting the flow of current through the circuit. The voltage source provides 'pressure' to drive electrons around the circuit. When the electrons meet resistance, work is performed. The electrons give up energy provided by the supply and the resistor heats up.

Think of the electrons in a circuit forming a continuous chain like that of a bicycle. The chain moves (electrons flow) when the supply voltage (pedal power) pushes them. Now imagine the bicycle brakes are applied (resistance in the circuit): there is resistance to the motion of the chain (current). This is fed back along the chain to the pedals and the rider feels that resistance and has to then push harder to keep the speed up. i.e. the resistance felt at the pedals is like a back e.m.f. opposing the electron flow and the chain effect means the supply has to work harder to keep the current flowing.

In this way and re-reading the original text, I hope you can see what it's trying to get at.

It should be noted, that with a purely resistive circuit, both applied voltage and current are in phase with each other.

Things get more complicated when inductance and capacitance are added in that the current no longer follows the AC supply voltage and either leads or lags the voltage. i.e. hence the term 'reactance' because the current reacts to the inductance or capacitance in a different way than to a pure resistance.

I agree with you though, the text is horribly written and confusing.
(edited 1 year ago)