Ray Optics and Optical Instruments
41 Board Physics previous year questions on Ray Optics and Optical Instruments — options free on every question; 4 include the answer & explanation free, the rest unlock with PYQ Pass.
A plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of \({f}_{1}\) in air. Another plano-convex lens with first surface radius of curvature 3 cm has focal length of \({f}_{2}\) when it is immersed in a liquid of refractive index 1.2 . If both the lenses are made of same glass of refractive index 1.5 , the ratio of \({f}_{1}\) and \({f}_{2}\) will be
[JEE Main 2025, 24 Jan (Shift 1)]
1:3
Using the lens maker's formula
\(\frac{1}{{f}_{1}}=\left({n}_{\text{glass }}-{n}_{\text{air }}\right)\left(\frac{1}{{R}_{1}}-\frac{1}{{R}_{2}}\right)\)
Since one surface is flat, \({R}_{2}\) is infinity, so
\(\frac{1}{{R}_{2}}=0\)
For the first lens in air (with refractive index 1.5 and radius of curvature 2 cm ):
\(\frac{1}{{f}_{1}}=(1.5-1)\left(\frac{1}{2}\right)\\ {f}_{1}=4cm\)
For the second lens:
\(\frac{1}{{f}_{2}}=\left(\frac{1.5}{1.2}-1\right)\left(\frac{1}{3}-0\right)\\ {f}_{2}=12cm\)
Ratio of focal lengths:
\({f}_{1}:{f}_{2}=4:12=1:3\)
A point object is placed in air at a distance of 4R on the principal axis of a convex spherical surface of radius of curvature R separating two mediums, air and glass. As the object is moved towards the surface, the image formed is :
first real and then virtual
To determine the nature of the image formed by a convex spherical surface separating air and glass, we need to consider the refraction of light at the convex surface. The nature of the image (real or virtual) depends on the position of the object relative to the focal point of the convex surface.
Identify the given parameters: object distance (\(u = -4R\)), radius of curvature (\(R\)), and the refractive indices of air (\(n1 = 1\)) and glass (\(n2 > 1\)).
Use the refraction formula for a spherical surface:
\(\frac{n_2}{v} - \frac{n_1}{u} = \frac{n_2 - n_1}{R}\)
where \(u\) is the object distance, \(v\) is the image distance, and \(R\) is the radius of curvature.
Substitute the given values into the formula:
\(\frac{n_2}{v} - \frac{1}{-4R} = \frac{n_2 - 1}{R}\)
Solve for the image distance \(v\). As the object moves towards the surface (\(u\) increases from \(-4R\) to \(0\)), analyze how the image distance \(v\) changes. Initially, when the object is far (\(u = -4R\)), the image is virtual. As the object moves closer to the surface, the image becomes real when the object is within the focal length of the convex surface.
Final Answer:
D. first real and then virtual
A beaker is filled with water (refractive index \(\frac{4}{3}\)) upto a height H . A coin is placed at its bottom. The depth of the coin, when viewed along the near normal direction, will be
\(\frac{3\mathrm{H}}{4}\)
The apparent depth (\({d}_{a}\)) is given by the formula:
\({d}_{a}=\frac{d}{n}\)
where \(d\)is the actual depth of the coin and \(n\) is the refractive index of the medium (water in this case).
\({d}_{a}=\frac{H}{\frac{4}{3}}\)
To solve this, multiply \(H\) by the reciprocal of \(\frac{4}{3}\):
\({d}_{a}=H\times \frac{3}{4}=\frac{3H}{4}\)
A concave mirror of focal length \(f\) in air is dipped in a liquid of refractive index \(\mu\). Its focal length in the liquid will be:
[JEE Main 2025, 23 Jan (Shift 2)]
\(f\)
There is no effect of medium on focal length of Spherical mirror.
A beaker is filled with water (refractive index \(\frac{4}{3}\)) upto a height H . A coin is placed at its bottom. The depth of the coin, when viewed along the near normal direction, will be
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Given a thin convex lens (refractive index \(\mu_2\) ), kept in a liquid (refractive index \({\mu }_{1},{\mu }_{1}<{\mu }_{2}\) ) having radii of curvatures \(\left|{\mathrm{R}}_{1}\right|\) and \(\left|{\mathrm{R}}_{2}\right|\). Its second surface is silver polished. Where should an object be placed on the optic axis so that a real and inverted image is formed at the same place?
[JEE Main 2025, 23 Jan (Shift 1)]
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The focal lengths of the objective and the eyepiece of a compound microscope are 1 cm and 2 cm respectively. If the tube length of the microscope is 10 cm , the magnification obtained by the microscope for most suitable viewing by relaxed eye is :
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A spherical surface of radius of curvature \(R\), separates air from glass (refractive index \(=1.5\) ). The centre of curvature is in the glass medium. A point object ' O ' placed in air on the optic axis of the surface, so that its real image is formed at ' I ' inside glass. The line OI intersects the spherical surface at P and \(\mathrm{PO}=\mathrm{PI}\). The distance PO equals to
[JEE Main 2025, 23 Jan (Shift 1)]
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What is the relative decrease in focal length of a lens for an increase in optical power by 0.1 D from 2.5D? ['D' stands for dioptre]
[JEE Main 2025, 24 Jan (Shift 1)]
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A concave mirror of focal length \(f\) in air is dipped in a liquid of refractive index \(\mu\). Its focal length in the liquid will be:
[JEE Main 2025, 23 Jan (Shift 2)]
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A plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of \({f}_{1}\) in air. Another plano-convex lens with first surface radius of curvature 3 cm has focal length of \({f}_{2}\) when it is immersed in a liquid of refractive index 1.2 . If both the lenses are made of same glass of refractive index 1.5 , the ratio of \({f}_{1}\) and \({f}_{2}\) will be
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The speed of light in two media ' 1 ' and ' 2 ' are \({v}_{1}\) and \({v}_{2}\left(>{v}_{1}\right)\) respectively. For a ray of light to undergo total internal reflection at the interface of these two media, it must be incident from
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Given a convex lens of refractive index \({\mu }_{2}\) in a liquid of refractive index \({\mu }_{1},{\mu }_{1}<{\mu }_{2}\) having radii of curvature \({\mathrm{R}}_{1},{\mathrm{R}}_{2}\mathrm{and}{\mathrm{R}}_{2}\) surface is silver polished. Where should an object be placed on the optical axis so that the real and inverted image is formed at the same place.
(Shift - I Memory Based)
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The focal lengths of the objective and the eyepiece of a compound microscope are 1 cm and 2 cm respectively. If the tube length of the microscope is 10 cm , the magnification obtained by the microscope for most suitable viewing by relaxed eye is :
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The optical power of a lens is increased from \(0.1\text{ }\text{D}\) to \(2.5\text{ }\text{D}\). What is the relative shift in the focal length of the lens?
(Shift I Memory Based)
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For a concave mirror, the distance between the object and image is 20 cm , and the magnification is -3 . Find the focal length of the mirror.
(Shift - II Memory Based)
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The speed of light in two media ' 1 ' and ' 2 ' are \({v}_{1}\) and \({v}_{2}\left(>{v}_{1}\right)\) respectively. For a ray of light to undergo total internal reflection at the interface of these two media, it must be incident from
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The speed of light in two media ' 1 ' and ' 2 ' are \({v}_{1}\) and \({v}_{2}\left(>{v}_{1}\right)\) respectively. For a ray of light to undergo total internal reflection at the interface of these two media, it must be incident from
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A spherical surface of radius of curvature \(R\), separates air from glass (refractive index \(=1.5\) ). The centre of curvature is in the glass medium. A point object ' O ' placed in air on the optic axis of the surface, so that its real image is formed at ' I ' inside glass. The line OI intersects the spherical surface at P and \(\mathrm{PO}=\mathrm{PI}\). The distance PO equals to
[JEE Main 2025, 23 Jan (Shift 1)]
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A beaker is filled with water (refractive index \(\frac{4}{3}\)) upto a height H . A coin is placed at its bottom. The depth of the coin, when viewed along the near normal direction, will be
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The refractive index of a prism with apex angle A is \(\cot \frac{A}{2}\). The angle of minimum deviation is :
[JEE Main 2024, 31 Jan (Shift 1)]
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What is the lateral shift of a ray refracted through a parallel-sided glass slab of thickness ' \(h\) ' in terms of the angle of incidence ' \(i\) ' and angle of refraction ' \(r\) ', if the glass slab is placed in air medium?
[JEE Main 2025, 23 Jan (Shift 1)]
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What is the relative decrease in focal length of a lens for an increase in optical power by 0.1 D from 2.5D? ['D' stands for dioptre]
[JEE Main 2025, 24 Jan (Shift 1)]
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A beaker is filled with water (refractive index \(\frac{4}{3}\)) upto a height H . A coin is placed at its bottom. The depth of the coin, when viewed along the near normal direction, will be
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A convex refracting surface curved towards medium A separates two media A and B, where medium A has a refractive index of 1.3 and medium B has a refractive index of 1.4. An object is placed 26 cm in medium A along the principal axis. If the image is formed at infinity, find the radius of curvature of the surface.
(Shift - II Memory Based)
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A point object is placed in air at a distance of 4R on the principal axis of a convex spherical surface of radius of curvature R separating two mediums, air and glass. As the object is moved towards the surface, the image formed is :
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Given is a thin convex lens of glass (refractive index \(\mu\) ) and each side having radius of curvature \(R\). One side is polished for complete reflection. At what distance from the lens, an object be placed on the optic axis so that the image gets formed on the object itself ?
[JEE Main 2025, 22 Jan (Shift 1)]
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A point object is placed in air at a distance of 4R on the principal axis of a convex spherical surface of radius of curvature R separating two mediums, air and glass. As the object is moved towards the surface, the image formed is :
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A thin prism \({P}_{1}\) with angle 4° made of glass having refractive index 1.54 , is combine with another thin prism \({P}_{2}\) made of glass having refractive index 1.72 to get dispersion without deviation. The angle of the prism \({P}_{2}\) in degrees is
(Shift - I Memory based)
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A plano-convex lens has a radius of curvature of 2 cm and a refractive index of 1.5. Its focal length is \({f}_{1}\) in air and \({f}_{2}\) in a medium with a refractive index of 1.2. Calculate the ratio \(\frac{{f}_{1}}{{f}_{2}}\).
(Shift - I Memory Based)
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The focal lengths of the objective and the eyepiece of a compound microscope are 1 cm and 2 cm respectively. If the tube length of the microscope is 10 cm , the magnification obtained by the microscope for most suitable viewing by relaxed eye is :
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If angle of prism is equal to the angle of minimum deviation. Given \(\mu =\sqrt{3}\), then find the angle of prism.
(Shift - II Memory Based)
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At the interface between two materials having refractive indices \({n}_{1}\) and \({n}_{2}\), the critical angle for reflection of an em wave is \({\theta }_{1C}\). The \({n}_{2}\) material is replaced by another material having refractive index \({n}_{3}\) such that the critical angle at the interface between \({n}_{1}\) and \({n}_{3}\) materials is \({\theta }_{2C}\). If \({n}_{3}>{n}_{2}>{n}_{1};\frac{{n}_{2}}{{n}_{3}}=\frac{2}{5}\) and \(\sin {\theta }_{2C}-\sin {\theta }_{1C}=\frac{–1}{2}\), then \({\theta }_{1C}\) is
[JEE Main 2025, 29 Jan (Shift 1)]
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Assertion (A) : Plane and convex mirrors cannot produce real images under any circumstance.
Reason (R) : A virtual image cannot serve as an object to produce a real image.
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Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R).
Select the correct answer from the codes (A), (B), (C) and (D)as given below.
Assertion (A) : Although the surfaces of a goggle lens are curved, it does not have any power.
Reason (R) : In case of goggles, both the curved surfaces are curved on the same side and have equal radii of curvature.
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Two statements are given - one labelled Assertion (A) and the other labelled Reason \((R)\). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A) : Plane and convex mirrors cannot produce real images under any circumstance.
Reason ( \(R\) ): A virtual image cannot serve as an object to produce a real image.
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Two statements are given - one labelled Assertion (A) and the other labelled Reason \((R)\). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A) : A convex lens, when immersed in a liquid, disappears.
Reason ( \(R\) ): The refractive indices of material of the lens and the liquid are equal.
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Assertion (A) and Reason (R) type questions. Two statements are given one labelled Assertion (A) and the other labelled Reason
(R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A) : The magnifying power of a compound microscope is negative.
Reason (R) : The final image formed is erect with respect to the object.
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A ray of monochromatic light propagating in air, is incident on the surface of water. Which of the following will be the same for the reflected and refracted rays?
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The radii of curvature for a thin convex lens are 10 cm and 15 cm respectively. The focal length of the lens is 12 cm. The refractive index of the lens material is:
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The magnifying power of a telescope with tube length \( 60 \mathrm{~cm} \) is 5 . What is the focal length of its eye piece ?
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