NEET Physics Question - Wave Optics - Young's Double Slit Experiment

Assertion (A): If in YDSE, wavelength of light used is increased, angular width remain unchanged only linear width of fringes increases.

Reason (R): Only linear fringe width proportional to wavelength and angular fringe width does not depends on wavelength.

(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)

(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

(3) (A) is true but (R) is false

(4) Both (A) and (R) are false

Solution:

In YDSE, angular fringe width is \(\beta_\theta = \frac{\lambda}{\text{d}}\) and linear fringe width is \(\beta = \frac{\lambda \text{D}}{\text{d}}\). Both are directly proportional to the wavelength \(lambda\). Thus, Assertion (A) is false as angular width also changes. Reason (R) is false as angular width does depend on wavelength.

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YDSE Wavelength and Fringe Width

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