Q.Write the circuit symbol and truth table for an OR gate.

The Intuition: "Any One Will Do"

Imagine you are at home and the doorbell rings. You want to know: Did someone press the doorbell? There are two possible buttons — one at the front gate and one at the back gate. If either button is pressed (or both), the bell rings. If neither is pressed, silence.

That is the OR gate in everyday life. It answers the question: "Is at least one of my inputs active?"

The Precise Definition

An OR gate is a digital logic gate with two or more inputs and one output. The output is 1 (HIGH) if at least one of its inputs is 1 (HIGH). The output is 0 (LOW) only when all inputs are 0 (LOW).

For two inputs $A$ and $B$, the output $Y$ is written as:

The Truth Table (Two-Input OR)

Notice the last row: both inputs are 1, yet the output is still 1. That is the Boolean rule — once you have at least one 1, the output locks to 1.

The Logic Symbol

In circuit diagrams, the OR gate looks like a curved body with a pointed output:

   A ──\
        )── Y = A + B
   B ──/

The curved left side suggests "any input can enter", and the single output on the right says "if any one of you is active, I am active."

Real-World Example

Think of a lift call button in a building. There are two floors: Ground (G) and First (F). If someone on either floor presses the call button, the lift comes. The lift controller has an OR gate:

• $G = 1$ (someone on ground floor presses) → lift comes
• $F = 1$ (someone on first floor presses) → lift comes
• $G = 1$ and $F = 1$ (both press) → lift still comes (it cannot come twice) …