Q.Draw the symbol and write the truth table and Boolean expression of a two-input NOR gate, and show how a NOR gate can be built by combining an OR gate with a NOT gate.

A NOR gate's symbol is the OR-gate symbol with a small inversion bubble added at its output tip. Its truth table is the row-for-row complement of the OR gate's own table: output $Y=1$ only in the single row where $A=0$ and $B=0$, and $Y=0$ in every other row. Its Boolean equation is $Y=\overline{A+B}$. Since $\overline{A+B}$ is literally 'NOT (A OR B)', a NOR gate is built directly by feeding an OR gate's output into a NOT gate. …

Take the OR gate's truth table and invert every output row; write the equation as the OR expression under …

• Forgetting to invert EVERY row of the OR truth table, inverting only some.
• Writing $Y=\overline{A}+\overline{B}$ (inverting the inputs, a different expression by De …