# AC and DC signals

If a AC+DC signal passes through a junction from where a capacitor is connected to ground and resistor is also connected from the same junction to the ground ,will the voltage measured across resistor and capacitor be same? IF yes then how?AC signal will pass through capacitor while dc signal through resistor...wont it make a difference?

From your description it sounds like you are looking at a resistor and capacitor in parallel with respect to a voltage source and that this voltage source can either be AC or DC. Correct this if my interpretation is wrong. Maybe something like this: simulate this circuit – Schematic created using CircuitLab

It is important ot remember that anytime you hook anything up directly across a volage source, it must have the same electric potential across its pins. You can view this as you are effectively measuring the voltage across the terminals of the voltage source. Similarly, two devices that are connected in parallel both must be at the same potential (or have the same voltage) across their terminals. You can again view this as you are effectively measuring the voltage of the source.

My other interpretation of your question is that you are asking if both types of current flow are going through these two devices in parallel, will the voltage be the same? If this was your question then you need to realize that there are only two types of current flow and voltage sources cannot produce both (at least not at the same time). If a signal contains postive and negative voltages, then it is definitionally AC. If a signal contains only positive voltages, then it is definitionally DC. (These are slightly oversimplified but represent the effective definitions). Following this, either source signal (AC or DC) will have a voltage across it so any components must also have that potential.

For the future you should clarify your questions a little more.

An AC signal simply means that your signal level is changing sinusoidaly. In your situation Both AC and DC signal will flow through resistor and Only AC through capacitor. Due to AC signal in both componants current in them will vary in them such that the voltage across them remain constant. Consider input voltage as,

$$V_i=a+bsinwt$$ $$I_r =\frac{a+bsinwt}{R}$$ $$V_c=C\frac{dV_i}{dt}=Cbcoswt$$

Therefore as these equation explained that current in both componants is different and hold it's value such that voltage across them remain input voltage.

Well it seems that you decribed a parallel RC circuit. The voltage will be the same. How? The components are in parallel. Please read about the superposition theorem: Link for the superposition theorem

Basically, the current over the resistor will have an Ac+DC component, while the capacitor's current will have only the AC component, value is depending on the frequency of the AC signal and capacitance. Again, check for the superposition theorem and the calculation of impedance in AC circuits.

Yes. Whenever two circuit elements are connected in parallel, the potential difference across them will be the same.

how? AC signal will pass through capacitor while dc signal through resistor...wont it make a difference?

Because the capacitor can sustain a DC voltage across it without passing any current.

And a resistor can sustain an AC voltage across it while passing much less current than a capacitor (when $C \gt\gt 1/\omega{}R$).