What system type has output directly proportional to input?

• A. Linear System
• B. Non-linear System
• C. Dynamic System
• D. Static System

Answer: (A)

Direct proportionality between input and output points to a linear response, where the output equals a constant gain times the input. In a linear system, doubling the input doubles the output, and the response to a sum of inputs is the sum of the responses (the superposition principle). This linear behavior is what makes the output directly proportional to the input across the input range. A non-linear system would not maintain this proportionality everywhere; a dynamic system involves time dependence or memory, so the current output can depend on past inputs; a static system is memoryless but can still be nonlinear. So the best fit is a linear system.