The duty cycle is defined as the proportion of on time relative to the total cycle time. Which expression correctly represents this ratio?

• A. On time divided by (on time plus off time)
• B. On time divided by off time
• C. On time plus off time
• D. On time multiplied by off time

Answer: (A)

The duty cycle is the fraction of a cycle during which the signal is ON. It compares the on-time to the total cycle time, so the expression is on-time divided by (on-time plus off-time). For example, if something is on for 2 ms and off for 3 ms in each cycle, the duty cycle is 2 / (2 + 3) = 0.4, or 40%. This shows what portion of each cycle the system is active. The other options don’t represent a ratio of on-time to total cycle duration: dividing by off-time ignores the total cycle length, adding on-time and off-time gives the cycle duration but not a ratio, and multiplying the two doesn’t yield a fraction of time.