Physics · Semiconductor Electronics : Materials, Devices And Simple Circuits · NEET
They are the two allowed voltage levels of a digital signal. 1 means HIGH (a fixed positive voltage, often taken as +5 V) and 0 means LOW (near 0 V). A logic gate only understands these two states - there is no value like 0.5 in between. This is why the signals are called binary (two levels).
An analog signal can take any value smoothly (like a wave), for example your voice. A digital signal has only two fixed levels, 0 and 1. Logic gates work only on digital signals. So before a gate can act, the information must already be in binary 0/1 form.
A truth table is a chart that lists every possible combination of the inputs and the output the gate gives for each. If a gate has 2 inputs, there are 2 to the power 2 = 4 input rows (00, 01, 10, 11). The truth table is the full definition of the gate - if you know the truth table, you know the gate. Almost every NEET logic-gate question is solved by building or reading a truth table.
A logic gate can have one or more inputs but always exactly one output. The NOT gate has just 1 input; AND, OR, NAND, NOR usually have 2 inputs (they can have more). No matter how many inputs, there is only a single output line.
Yes. Even though the latest rationalised NCERT trimmed some digital-electronics text, NEET has asked logic-gate questions every year from 2019 to 2025 (AND, OR, NOT, NAND, NOR, truth tables and Boolean output). So this topic is scoring and must not be skipped.
No. A diode or transistor is a single component. A logic gate is a small circuit (often built using diodes and transistors) that performs a logic operation. Think of the gate as the finished tool, and diodes/transistors as the parts used to build it.
A logic circuit provides the output Y as per the following truth table: for inputs (A,B) = (0,0),(0,1),(1,0),(1,1) the outputs Y are 1,0,1,0. The expression for the output Y is:
The output (Y) of the given logic gate (each input first inverted, then both fed to a NOR gate) is similar to the output of an/a:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a tiny digital circuit that reads binary inputs (0 or 1) and gives one binary output (0 or 1) using a fixed rule. It is the basic building block of all digital devices like calculators and computers.
The three basic gates are AND, OR and NOT. From these we build the universal gates NAND and NOR. NEET asks about all five.
They are directly asked in NEET Physics almost every year (2019-2025). Questions are quick and formula-free - you mainly build or read a truth table, so they are easy marks once you know the rules.
Binary means only two possible values: 0 and 1. Here 1 stands for HIGH voltage (like +5 V) and 0 stands for LOW voltage (near 0 V). Logic gates work only with these two states.
Make a truth table. Write every input combination (00, 01, 10, 11 for two inputs), apply the gate rules step by step through the circuit, and read off the output column. Then match it with the options.
