Which system type has output not directly proportional to input?

• A. Non-linear System
• B. Linear System
• C. Cyclic System
• D. Proportional System

Answer: (A)

Direct proportionality means output changes at a constant multiple of the input. When that isn't the case, the system is non-linear. In a non-linear system, the relationship between input and output isn’t a straight line: doubling the input might more than double the output, less than double it, or even produce a completely different pattern (like quadratic, exponential, or saturated responses). That variability in the ratio y/x with different input levels is what defines non-linearity.

Linear systems have output = k times input, so the ratio stays constant. A system described as cyclic relates to repeating behavior over time and doesn’t inherently address proportionality, and a system described as proportional would imply direct proportionality by definition. So the non-linear option best fits the idea of output not being directly proportional to input.