A Lissajous patterns on a Cathode Ray Oscilloscope (CRO) has 8 vertical maximum values and 4 horizontal maximum values. The frequency of the horizontal input is 1600 Hz. Determine the frequency of the vertical input?

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  1. 200 Hz
  2. 800 Hz
  3. 600 Hz
  4. 400 Hz

Answer (Detailed Solution Below)

Option 2 : 800 Hz
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Concept:

Lissajous patterns on a CRO are used to determine the frequency ratio of two sinusoidal signals. The ratio of frequencies is given by:

\( \frac{f_y}{f_x} = \frac{\text{Number of vertical tangencies}}{\text{Number of horizontal tangencies}} \)

Given

Number of vertical maximum values = 8

Number of horizontal maximum values = 4

Horizontal frequency (\( f_x \)) = 1600 Hz

Calculation

\( \frac{f_y}{1600} = \frac{8}{4} = 2 \)

\( f_y = 2 \times 1600 = 3200\ \text{Hz} \)

However, the number of vertical loops (or vertical maxima) is **8**, and horizontal is **4**, so:

\( \frac{f_x}{f_y} = \frac{8}{4} = 2 \Rightarrow f_y = \frac{f_x}{2} = \frac{1600}{2} = 800\ \text{Hz} \)

 

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