welcome to lecture online with this video we're starting a new series in electrical engineering on RC and RL circuits now what are RC and RL circuits the R stands for resistance the C stands for capacitance and the L stands for inductance now notice here we have two examples one circuit that has a capacitor and the resistor so therefore we call that an RC circuit and here we have an inductor and a resistor we call that an RL circuit in this chapter we're not yet going to mix capacitors inductors and resistors all in the same circuit because then you end up with a different kind of circuit here our C circuits and our L circuits are known as first-order circuits the reason for that is when you try to calculate the current through a capacitor you find that it's defined as being the capacitance times the change in the voltage over time and here if you're trying to find the voltage across an inductor it is equal to the inductance times changed in the current through the inductor with respect to time and therefore when we did when we try to put together a an equation that defines the voltage in an RC circuit or an equation that defines the current in an RC circuit you end up with a first-order differential equation hence the name first-order circuits in the next chapter we'll deal with second order to order circuits when we combine capacitors inductors and resistors all in the same circuit now let's start with the relatively easier type of circuit and easier type of differential equation now what this is all about in this chapter is we're going to learn how to calculate the current through any of the branches and the voltage across any of the branches and of course we'll see more complicated examples than what we have over here but we need to learn how to find the current and the voltage in these various types of circuits again limiting the circuit to either being resistors and capacitors and or I should say resistors and inductors so that's what we're going to do in this section so if you're interested in it stay tuned we'll have lots of more videos on this topic