Question

The two inputs of a CRO are fed with two stationary periodic signals. The figure changes from ellipse to circle and back to ellipse with its major axis changing orientation slowly and repeatedly. The following inference can be made from this.

(a) The signals are not sinusoidal in nature

(b) The amplitudes of the signals are very close but not equal

(c) The signals are sinusoidal with their frequencies very close but not equal

(d) There is a constant but small phase difference between the signals

The question was posed to me in an interview for job.

This interesting question is from Advanced Problems on CRT and CRO in division Oscilloscopes of Electrical Measurements

Answer 1

Right option is (d) There is a constant but small phase difference between the signals

To explain: X = A sinωt

Y = A sin (ωt-∅t)

Phase difference = ∅t

For ellipse, A1 ≠ A2

For circle, A1 = A2

Hence, there is a constant but small difference between the signals.