The Lissajous pattern observed in a CRO is shown here. What is the frequency ratio of the vertical signal to the horizontal signal?

This question was previously asked in

DMRC AM Electrical Official Paper 2020

Option 3 : 4 : 1

ST 1: Building Materials

1159

20 Questions
20 Marks
20 Mins

Concept:

The following is a procedure to measure the frequency of a Lissajous pattern obtained form CRO.

- For a given Lissajous figure, draw both horizontal and vertical lines passing through the Lissajous figure (Never draw either horizontal line (or) vertical line via pre-existing intersection in the Lissajous figure)
- Count the number of cuts made by both lines
- The unknown to known frequency ratio can be measured as follows.

\(\dfrac{{{f_v}}}{{{f_h}}} = \dfrac{{{n_h}}}{{{n_v}}}\)

Where

fv = unknown vertical frequency

fh = known horizontal frequency

nh = no. of cuts as made by horizontal

nv = no. of cuts as made by a vertical line

Calculation:

From the given Lissajous figure,

Vertical cuts (nv) = 2

Horizontal cuts (nh) = 8

The frequency ratio of the vertical signal to the horizontal signal is

\(\dfrac{{{f_V}}}{{{f_H}}} = \dfrac{{{n_h}}}{{{n_v}}} = \dfrac{8}{2} = \dfrac{4}{1}\)