Rise time is defined as the time it takes for the output to go from what fraction to what fraction of its maximum value?

Rise time is defined as the time it takes for the output to go from what fraction to what fraction of its maximum value?

• A. A 0.0 to 1.0
• B. B 0.5 to 0.95
• C. C 0.1 to 0.9
• D. D 0.2 to 0.8

Answer: (C)

Rise time tells you how quickly a system’s output climbs from its initial level to its final, steady value after a step input. The standard definition uses the interval from 10% to 90% of the final value, because it captures the main part of the transition while avoiding the effects of the very start (where delays can dominate) and the final plateau (which can be noisy or influenced by the settling process).

For a simple first‑order response V(t) = Vf(1 − e^(−t/τ)), the times to reach 10% and 90% are t10 ≈ 0.105τ and t90 ≈ 2.303τ, so the rise time t_r = t90 − t10 ≈ 2.20τ. This shows why 10% to 90% is used: it reflects the characteristic speed of the transition without being tied to the exact initial delay or final overshoot.

So the rise time corresponds to the time for the output to go from 10% to 90% of its maximum value.