# Direct current circuits 16 1 and resistance relationship

### Introduction to circuits and Ohm's law (video) | Khan Academy

Chapter 16 - RC and L/R Time Constants In a series RC circuit, the time constant is equal to the total resistance in ohms If plotted on a graph, the approach to the final values of voltage and current Since the time constant (τ) for an RC circuit is the product of resistance and capacitance, we obtain a value of 1 second. For this issue, every electronics / electrical circuit consist three basic . In this graph If R = 1 then the current and Voltage will increase. DIRECT-CURRENT CIRCUITS. § initially. Positive work has been done on the . this is the relationship between the equivalent resistance R and the individ - .. A voltmeter having a resistance of , ohms and a full-scale.

If only we knew what the total resistance was for the circuit: This brings us to the second principle of series circuits: This should make intuitive sense: Knowing this, we could re-draw the circuit with a single equivalent resistor representing the series combination of R1, R2, and R3: Knowing that current is equal through all components of a series circuit and we just determined the current through the batterywe can go back to our original circuit schematic and note the current through each component: Notice the voltage drops across each resistor, and how the sum of the voltage drops 1.

This is the third principle of series circuits: However, the method we just used to analyze this simple series circuit can be streamlined for better understanding. You begin your analysis by filling in those elements of the table that are given to you from the beginning: The 9 volts of battery voltage is not applied directly across R1, R2, or R3.

In this case, we can use the series rule of resistances to determine a total resistance from the sum of individual resistances: Well, the water's immediately gonna drop straight down. That potential energy is gonna be converted to kinetic energy. And you could look at a certain part of the pipe right over here, right over here. And you could say, well, how much water is flowing per unit time? And that amount of water that is flowing through the pipe at that point in a specific amount of time, that is analogous to current.

Current is the amount of charge, so we could say charge per unit time. Q for charge, and t for time. And intuitively you could say, how much, how much charge flowing, flowing past a point in a circuit, a point in circuit in a, let's say, unit of time, we could think of it as a second.

**Introduction to circuits and Ohm's law - Circuits - Physics - Khan Academy**

And so you could also think about it as coulombs per second, charge per unit time. And the idea of resistance is something could just keep that charge from flowing at an arbitrarily high rate.

And if we want to go back to our water metaphor, what we could do is, we could introduce something that would impede the water, and that could be a narrowing of the pipe. And that narrowing of the pipe would be analogous to resistance.

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.

## Voltage and Current Calculations

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.

- Introduction to circuits and Ohm's law
- Simple Series Circuits

And so we can provide a path. 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. This tells us that current has decreased rather than increased with the passage of time. Since we started at a current of 1. Either way, we should obtain the same answer: Using the Universal Time Constant Formula for Analyzing Inductive Circuits The universal time constant formula also works well for analyzing inductive circuits.

If we start with the switch in the open position, the current will be equal to zero, so zero is our starting current value. If we desired to determine the value of current at 3. Given the fact that our starting current was zero, this leaves us at a circuit current of Subtracted from our battery voltage of 15 volts, this leaves 0.

### Simple Series Circuits | Series And Parallel Circuits | Electronics Textbook

Identify the quantity to be calculated whatever quantity whose change is directly opposed by the reactive component. For capacitors this is voltage; for inductors this is current. Determine the starting and final values for that quantity.

Plug all these values Final, Start, time, time constant into the universal time constant formula and solve for change in quantity.