# Relationship between current resistance and capacitance

### Introduction to circuits and Ohm's law (video) | Khan Academy How electrical charge relates to voltage, current, and resistance. a quick way to reference the relationship between voltage, current, resistance, and power. George Simon Ohm discovered the relationship between current, Impedance includes resistance, capacitive reactance, and inductive. The electrical resistance of a circuit component is defined as the ratio of the applied voltage to the electric current that flows through it.

So in this situation, once again, I have my vertical water pipe, I have opened it up, and you still would have that potential energy, which is analogous to voltage, and it would be converted to kinetic energy, and you would have a flow of water through that pipe, but now at every point in this pipe, the amount of water that's flowing past at a given moment of time is gonna be lower, because you have literally this bottleneck right over here.

So this narrowing is analogous to resistance. How much charge flow impeded, impeded. And the unit here is the ohm, is the ohm, which is denoted with the Greek letter omega. So now that we've defined these things and we have our metaphor, let's actually look at an electric circuit. So first, let me construct a battery. So this is my battery. And the convention is my negative terminal is the shorter line here.

So I could say that's the negative terminal, that is the positive terminal. Associated with that battery, I could have some voltage.

### Resistors (Ohm's Law), Capacitors, and Inductors - Northwestern Mechatronics Wiki

And just to make this tangible, let's say the voltage is equal to 16 volts across this battery. And so one way to think about it is the potential energy per unit charge, let's say we have electrons here at the negative terminal, the potential energy per coulomb here is 16 volts. These electrons, if they have a path, would go to the positive terminal. And so we can provide a path.

Electrical Engineering: Ch 6: Capacitors (8 of 26) Current - Voltage Relationship (2 of 2)

Let me draw it like this. At first, I'm gonna not make the path available to the electrons, I'm gonna have an open circuit here. I'm gonna make this path for the electrons. And so as long as our circuit is open like this, this is actually analogous to the closed pipe. The electrons, there is no way for them to get to the positive terminal.

But if we were to close the circuit right over here, if we were to close it, then all of a sudden, the electrons could begin to flow through this circuit in an analogous way to the way that the water would flow down this pipe.

Now when you see a schematic diagram like this, when you just see these lines, those usually denote something that has no resistance.

But that's very theoretical. In practice, even a very simple wire that's a good conductor would have some resistance. And the way that we denote resistance is with a jagged line.

## Voltage and Current Calculations

And so let me draw resistance here. So that is how we denote it in a circuit diagram. Now let's say the resistance here is eight ohms. So my question to you is, given the voltage and given the resistance, what will be the current through this circuit?

What is the rate at which charge will flow past a point in this circuit?

### Voltage and Current Calculations | RC and L/R Time Constants | Electronics Textbook

For capacitorsthis quantity is voltage; for inductorsthis quantity is current. The final value for this quantity is whatever that quantity will be after an infinite amount of time.

Calculating the Time Constant of a Circuit The next step is to calculate the time constant of the circuit: In a series RC circuitthe time constant is equal to the total resistance in ohms multiplied by the total capacitance in farads.

The rise and fall of circuit values such as voltage and current in response to a transient is, as was mentioned before, asymptotic.

Being so, the values begin to rapidly change soon after the transient and settle down over time. If plotted on a graph, the approach to the final values of voltage and current form exponential curves. As was stated before, one time constant is the amount of time it takes for any of these values to change about 63 percent from their starting values to their ultimate final values. For every time constant, these values move approximately 63 percent closer to their eventual goal.

The mathematical formula for determining the precise percentage is quite simple: It is derived from calculus techniques, after mathematically analyzing the asymptotic approach of the circuit values. The more time that passes since the transient application of voltage from the battery, the larger the value of the denominator in the fraction, which makes for a smaller value for the whole fraction, which makes for a grand total 1 minus the fraction approaching 1, or percent. The symbol for a resistor: Try wikipedia for more on resistors and for the resistor color codes. The relationship between the current through a conductor with resistance and the voltage across the same conductor is described by Ohm's law: The power dissipated by the resistor is equal to the voltage multiplied by the current: If I is measured in amps and V in volts, then the power P is in watts. The potential on the straight side with the plus sign should always be higher than the potential on the curved side.

Notice that the capacitor on the far right is polarized; the negative terminal is marked on the can with white negative signs. The polarization is also indicated by the length of the leads: A capacitor is a device that stores electric charges. The current through a capacitor can be changed instantly, but it takes time to change the voltage across a capacitor.