 Welcome to Truth Tables. In this video, you'll learn how to use and construct a truth table for digital devices. A truth table is a formal specification chart that describes the exact output behavior of a circuit for every possible set of input conditions. It is often used to show the operation of a particular circuit because its graphical characteristics are much easier to understand than a worded explanation. Truth tables are often used to describe the operation of a logic circuit. A truth table consists of an input section and an output section. Below is the truth table for the series circuit on the right that represents a two input AND gate. It is two switches that function as the inputs and one light bulb that serves as the output. A closed switch represents a logic 1 input signal and the light bulb turned on represents a logic 1 at the output. Observe how the truth table illustrates each possible set of inputs and their corresponding output. The only time the light bulb is on is when both switches are closed. When developing a truth table, the first step is to determine the number of inputs of the circuit. By using this number as the exponent for the binary number 2, the number of possible input combinations of 1s and 0s applied to the input is determined. Suppose a hypothetical logic device has three inputs and four outputs, as shown at the right. Since there are two possible binary states that exist at each input, and since there are three different input terminals, there are a total of eight different sets of 1s and 0s that can be applied. A digital circuit with five inputs will have 32 different combinations of binary numbers that can be applied. When determining the number of rows in the truth table, the number of outputs doesn't matter. To ensure that all possible combinations are written in the input section of the truth table, the 1s and 0s should be written in a binary counting sequence, as shown below, for a three input device. Now you give it a try. Choose the letter that matches the correct answer. You can pause the video if you need more time to think about your answer. The truth table graphically describes the operation of a circuit by showing the inputs and outputs, answer C. A digital circuit with four inputs will have 16 different possible combinations of binary numbers applied. This was answer C. This completes the video truth tables. Thanks for watching.