A periodic event occurs 240 times per second. What is its period in seconds?

• A. 0.0042 s
• B. 0.42 s
• C. 4.2 s
• D. 24 s

Answer: (A)

Period is the time for one cycle, and it equals the reciprocal of frequency: T = 1/f. If something happens 240 times per second, f = 240 Hz, so T = 1/240 s ≈ 0.0041667 s, which rounds to 0.0042 s. Thus the period is 0.0042 s. The other values would correspond to much longer periods (lower frequencies) and don’t match the reciprocal relationship.