Question E7A10:
What is a truth table?  

Choices:  
A: A list of inputs and corresponding outputs for an op-amp  
B: A list of inputs and corresponding outputs for a digital device  
C: A diagram showing logic states when the digital gate output is true  
D: A table of logic symbols that indicate the logic states of an op-amp    

Correct Answer is  B: A list of inputs and corresponding outputs for a digital device  

Correct answer: B — A list of inputs and corresponding outputs for a digital device

1) Why B is correct
- A truth table enumerates all possible combinations of digital inputs and shows the resulting output(s) of a logic function or device.
- It fully defines the behavior of a digital gate or circuit.

Example (2-input AND gate):
- 00 → 0
- 01 → 0
- 10 → 0
- 11 → 1

2) Why the other choices are incorrect
- A: Op-amps are analog devices; their behavior isn’t defined by discrete input/output combinations in a truth table (unless used as a comparator, but that’s not the standard meaning).
- C: A “diagram showing logic states when the digital gate output is true” is not a truth table; that sounds more like a conditional diagram or timing diagram, and it omits cases where the output is false.
- D: A “table of logic symbols” for an op-amp is unrelated; truth tables don’t list symbols, they list input/output relationships.

3) Useful formulas and rules of thumb
- For $n$ independent binary inputs, a complete truth table has $2^n$ rows.
- Truth tables can have multiple output columns for multi-output devices.
- You can derive Boolean expressions (SOP or POS) directly from a truth table.