Question

X and Y plates of a CRO are connected to unequal voltages of equal frequency with phase shift of $90^\circ$. The Lissajous pattern observed on the CRO screen is ............

• A. circle
• B. straight line
• C. ellipse
• D. figure of eight

Hint:

For Lissajous figures: equal frequency + $90^\circ$ phase + unequal amplitude $⇒$ ellipse.

Answer 1

The Correct Option is C

Lissajous patterns are formed on the CRO screen when two sinusoidal voltages are applied to the X and Y plates.
If the voltages are of equal frequency and phase shift is $90^\circ$ but their amplitudes are unequal, the resulting pattern is an ellipse.
- If the amplitudes were equal, the pattern would be a perfect circle.
- If there were no phase shift, the pattern would be a straight line.
- A figure of eight (or more complex loops) is seen with multiple frequency ratios.
Since unequal amplitudes and $90^\circ$ phase shift are specified, the correct answer is an ellipse.