Advanced Qualification · A-003 Measurements · A-003-005-008
A 100-kHz signal is applied to the horizontal channel of an oscilloscope. A signal of unknown frequency is applied to the vertical channel. The resultant wave form has 5 loops displayed vertically and 2 loops horizontally. The unknown frequency is:
- A 20 kHz
- B 50 kHz
- C 30 kHz
- D 40 kHz
Correct answer: D — 40 kHz. From the official ISED question bank, verified word for word.
Why
The unknown frequency is 40 kHz because the oscilloscope shows a Lissajous pattern where the ratio of vertical loops to horizontal loops equals the ratio of the unknown frequency to the known 100 kHz signal. The full explanation — and one for every question — is in Pro.
Practise this section
Measurements: meters, oscilloscopes, counters, signal generators, and what a reading actually tells you.