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The two inputs of a CRO are fed with two stationary periodic signals. In the X-Y mode, the screen shows a figure below which changes from ellipse to circle and back to ellipse with its major axis changing orientation slowly and repeatedly. Which of the following inference can be made from this?
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- The signals are not sinusoidal
- The amplitudes of the signals are very close but not equal
- The signals are sinusoidal with their frequencies very close but not equal
- There is a constant but small phase difference between the signals
Correct Option: D
The signals are sinusoidal with their frequency very close but not equal The phase difference of two signals is varying li
nearly with time. So we can write.
X = A sin ωt
Y = A sin (ωt – φ)
∴ Phase difference = φ
Alternately
X = A1 sin ωt
Y = A2 cosωt = A2 sin (ωt – φ)
For ellipse, A1 ≠ A2
For circle, A1 = A2
