Title 09. RAY OPTICS AND OPTICAL INSTRUMENTS.pdf ✅

09. RAY OPTICS AND OPTICAL INSTRUMENTS NEET PREPARATION (MEDIUM PHYSICS PAPER) Date: March 12, 2025 Dura on: 1:00:00 Total Marks: 180 INSTRUCTIONS INSTRUCTIONS PHYSICS 1. () : Explana on For the surface , The angle between ray 2 and 3 is 2. () : Explana on or . 3. () : Explana on A concave mirror and a convex lens both have the same focal length in air. This is incorrect. Concave mirrors and convex lenses do not in‐ herently have the same focal length in air. Their focal lengths depend on the radii of curvature of their surfaces and the refrac ve indices of the surrounding media. The refrac ve index of water is smaller than the refrac ve index of air. This is not correct. In re‐ ality, the refrac ve index of water (typically around 1.33) is greater than the refrac ve index of air (which is approximately 1). Therefore, the Reason's explana on is incorrect. The correct explana on is that the focal length of a mirror doesn't depend on the refrac ve in‐ dex of the surrounding medium, while the focal length of a lens does depend on the refrac ve index of the surrounding medium. As a result, when a lens is submerged in a medium with a higher refrac ve index (like water), its focal length increases. The Asser on is correct in sta ng that the concave mirror and convex lens may have the same focal length in air, but the Reason's explana on is not accurate. AC √3 sin 30 0 = sin r⇒ r = 60 0 90 ∘ P = P1 + P2 = 2.5 − 3.75 P = −1.25D P = 100 f f = = −80 cm 100 −1.25
4. () : Explana on The apparent distance of the surface of water for the fish Also, from the surface, the bird is at an appar‐ ent distance . The total apparent distance 5. () : Explana on In this case, the light gets refracted twice Air-ice interface. From Snell’s law At Ice-glass interface From eq’s (1) and (2) From eq’s (1) and (2) Also, refrac ve index of ice w.r.t. glass So, the correct op on is (2) 6. () : Explana on Given that 7. () : Explana on For improving far point, concave lens is re‐ quired and for this concave lens So The posi on of near point for which the image is formed at is. 8. () : Explana on and 9. () : Explana on . 10. () : Explana on Given that 11. () : Explana on Focal length depends upon as Three materials are use to make a lens so there should be three focal lengths then three images will be produced. 12. () : Explana on The path traced by the light ray is shown in the figure. By applying Snell’s law at and From the above equa on’s we get = x ny ∴ = x + ny = sin 60 ∘ sin r1 μice 1 ⇒ sin r1 = = = (1) sin 60 ∘ μice √3/2 4/3 3√3 8 μIce sin r1 = μglass sin r2 (2) ⇒ sin r2 = = = = ( ) sin 60 ∘ μglass (√3/2) 1.5 √3/2 3/2 1 √3 ⇒ μice,glass = = = μice μglass 4/3 3/2 8 9 μw = 1.33, μg = 1.5 & μd = 2.4 μ w d = = 1.8 & μ d g = = = 0.625 μd μw μg μd 1.5 2.4 u = ∞, v = −30 cm 1 = − ⇒ f = −30 cm f 1 −30 1 ∞ 15cm = − 1 −30 1 −15 1 u ⇒ u = −30 cm = − 1 f 1 v 1 u ⇒ f = −20cm u = −25 cm, v = −100 cm ⇒ f = −20 cm P = = 5D 100 20 μ = sin( ) δmin + A 2 sin A 2 μ = sin( ) 30 + 60 2 sin 60 2 μ = = √2 sin 45 ∘ sin 35 ∘ μ = sin (A+δ) 2 sin A 2 δ = A = ⇒ cos = 3 2 2 sin cos A 2 A 2 sin A 2 A 2 3 4 A = 2cos−1 ( ) = 82 ∘ 42 3 ′ 4 μ = (μ − 1) ( − ) 1 f 1 R1 1 R2 A B sin 60 ∘ = μ sin r μ sin r = sin 2r r = 30 ∘&μ = √3

23. () : Explana on As we known As, . 24. () : Explana on If refrac ve index of lens is equal to refrac‐ ve index of liquid , then lens behaves as a plane glass plate and becomes invisible in the medium. 25. () : Explana on Shi 26. () : Explana on Convex mirror always produces virtual image in air. Correct op on is (1). 27. () : Explana on The propaga on of light ray through a prism is shown below When a light ray travel from air (rarer) to prism filled with water (denser) of higher redfrac ve index, then it bends towards the normal inside it. At other fae, the light is travelling from denser to rarer medium, so it bends away from normal. Thus, the prsim deviates the incident ray towards the base of prism as shown in fig‐ ure above. 28. () : Explana on We know that So red colour comes first 29. () : Explana on Given , 30. () : Explana on The light gathering power (or brightness) of a telescope So by increasing the objec ve diameter even stars may produce im‐ ages of op mum brightness. So op on (2) is correct. 31. () : Explana on and 32. () : Explana on If the mirror is rotated by then the light spot (reflected ray) rotates by i = 60 ∘ , A = 30 ∘ , δ = 30 ∘ i + e = A + δ e = A + δ − i = A + δ − i = 30 ∘ + 30 ∘ − 60 ∘ e = 0 ∘ , r2 = 0 ∘ r1 + r2 = A ∴ r1 = 30 ∘ μ = ⇒ = √3 = 1.732 sin i sin r sin 60 ∘ sin 30 ∘ μ = 1.732 n1 n2 = d (1 − μ 1 ) = 30 (1 − 1 ) = 10 cm 1.5 μV iolet > μRed ⇒ vRed > vV iolet sin 60 ∘ = μ sin r1 μ = sin i sin r i = 2r μ = 2 cos r ⇒ μ = = sin 2r sin r 2 sin r ⋅ cos r sin r r = cos−1( ) μ 2 ∴ i = 2 cos−1( ) μ 2 ∝ (diameter) 2 . m = f0 fe L = f0 + fe ⇒ = 50 f0 fe f0 + fe = 102 ⇒ f0 + = 102 f0 50 ⇒ f0 = 100 ⇒ fe = 2 Pe = = 50D, P0 = = 1m−1 = 1D 100 2 1 1m 2θ. 2θ = ; θ = y x y 2x