Practice portal › Alternating Current › Alternating Quantities: RMS and Mean

In an A.C. circuit the direction of the electric current gets reversed after every 2×10⁻² s. What is the frequency of the A.C.?

Asked in GSEB Board March 2016 · Instantaneous values and timing

• (1) 100 Hz
• (2) 3.14 Hz
• (3) 314 Hz
• (4) 25 Hz

Step-by-step solution

Why the other options are wrong

• (1) Halves the interval instead of doubling it: T = (2×10⁻²)/2 = 10⁻² s gives 100 Hz. A cycle contains two reversals, so the period is twice the interval.
• (2) No single slip gives 3.14 Hz. Sanity check: two reversals per cycle make T = 4×10⁻² s, and 1/T = 25 Hz.
• (3) Takes 2×10⁻² s as the full period and then quotes (2π)/T = 314, which is an angular frequency in rad s⁻¹, not a frequency in hertz. The period is wrong too: it is twice the reversal interval.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.