Question

X and Y plates of a CRO are connected to unequal voltages of equal frequency with phase shift of 90°. The Lissajous figure on the screen will be?

(a) Circle

(b) Straight line

(c) Ellipse

(d) Figure of eight

I had been asked this question in quiz.

Enquiry is from Advanced Problems on CRT and CRO topic in chapter Oscilloscopes of Electrical Measurements

Answer 1

Right option is (c) Ellipse

For explanation: The pattern observed on the CRT, when two sinusoidal signals are applied to the X-X and Y-Y plates of the CRT are known as Lissajous pattern.

sin φ = \(\frac{y_1}{y_2} = \frac{X_1}{X_2}\)

Here, the voltages are unequal and frequencies are equal with a phase shift of 90°. Therefore the Lissajous figure on the screen will be an ellipse.