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:

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 is section A-003 of the Advanced exam: Measurements: meters, oscilloscopes, counters, signal generators, and what a reading actually tells you.

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