Resolving Power and Wavelength – Rankers Physics

Diffraction: Practice Problem & Solution

Assertion (A): On increasing wavelength of light used, resolving power increases. Reason (R): On increasing wavelength, width of central maxima decreases.  
(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

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Diffraction. Understanding the underlying formula is key to arriving at the correct answer below:

Assertion (A) is false. Resolving power of optical instruments (e.g., telescope, microscope) is inversely proportional to the wavelength (\(RP \propto 1/\lambda\)). So, increasing wavelength decreases resolving power. Reason (R) is also false. In diffraction, the width of the central maximum is directly proportional to the wavelength (\(w \propto \lambda\)). Thus, increasing wavelength increases the width of the central maximum.

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