The power of a lens is defined as the reciprocal of its focal length in meters. It indicates the degree of convergence or divergence of light rays produced by the lens. Its SI unit is the dioptre (D).
More Questions on Light – Reflection and Refraction
1An object is placed at the center of curvature of a concave mirror. If the radius of curvature is 20 cm, what is the position of the image?
→ 2What is the principal focus (F) of a concave mirror?
→ 3A convex lens of focal length 10 cm forms a virtual image 15 cm from the lens. Where is the object placed?
→ 4What is the difference between real and virtual images?
→ 5A light ray passes through a prism. Does it deviate towards the base or away from the base of the prism?
→ 6Assertion (A): It is easier to see through fog or smoke when a powerful beam of light is used. Reason (R): Fog and smoke particles scatter blue light more effectively than red light.
→ 7A man is standing in a room and can see his full image in a plane mirror. If the man's height is H, what is the minimum height of the plane mirror required?
→ 8What happens to the focal length of a spherical mirror if it is immersed in water?
→ 9Explain how the lateral displacement changes for a light ray passing through a glass slab if the thickness of the slab increases.
→ 10An object of height 5 cm is placed 20 cm in front of a concave mirror which produces a real image of height 10 cm. Find the focal length of the mirror.
→ 11What is the common term for a lens that has a positive focal length and always forms a real image when the object is beyond its focal length?
→ 12A student places a pencil at the focal point of a concave mirror. What will be the nature of the reflected rays?
→ 13An object is placed 10 cm from a convex lens of focal length 15 cm. Describe the characteristics of the image formed.
→ 14Why does a coin appear to rise when water is poured into a mug where the coin is initially not visible?
→ 15Two mirrors, one concave and one convex, both have the same focal length magnitude. If an object is placed at the same distance (less than focal length) from both, compare the nature of the images formed.
→ 16What happens to the light ray that passes through the principal focus of a concave lens?
→ 17A light ray passes from a medium A to a medium B. If the speed of light in medium A is greater than that in medium B, what can be concluded about the refractive indices?
→ 18Why are the headlights of a car fitted with concave mirrors?
→ 19If an object is placed at 2F of a convex lens, and a screen is placed at 2F on the other side, what will be the magnification of the image?
→ 20Define the term 'optical center' of a lens.
→ 21A concave mirror is used in a torch. Where is the bulb usually placed relative to the mirror?
→ 22Assertion (A): The absolute refractive index of a medium is always greater than or equal to 1. Reason (R): The speed of light in any medium is always less than or equal to the speed of light in vacuum.
→ 23What is the significance of the pole (P) in spherical mirrors?
→ 24If a beam of parallel light rays is incident on a concave lens, what happens to the rays after refraction?
→ 25Compare the field of view of a plane mirror with that of a convex mirror of the same size.
→ 26What is the condition for a lens to have infinite focal length?
→ 27A convex lens is used to produce a real, inverted image of a candle flame. If the object distance is 30 cm and the image distance is 60 cm, calculate the focal length of the lens.
→ 28An object is placed at the 2F position of a concave lens. Describe the characteristics of the image formed.
→ 29Assertion (A): Convex mirrors are used in street lights. Reason (R): They diverge light over a large area.
→ 30What is the range of possible values for the refractive index of a medium (excluding vacuum)?
→ 31A light ray is incident on a plane mirror at an angle of 40° with the mirror surface. What is the angle of reflection?
→ 32Explain why a converging lens is sometimes called a "burning glass."
→ 33The image formed by a mirror is always virtual, erect, and diminished. What type of mirror is it?
→ 34An object is placed at the focus (F) of a concave mirror. Where is the image formed?
→ 35What is the angle of deviation when a light ray passes through the center of curvature of a spherical mirror?
→ 36A diverging lens always produces a virtual image. Where is this image located relative to the lens and object?
→ 37Why does a fish in water appear shallower than its actual depth?
→ 38If the refractive index of water is 4/3, and that of glass is 3/2, what is the refractive index of glass with respect to water?
→ 39An object is placed between the focal point (F) and the center of curvature (C) of a concave mirror. Describe the characteristics of the image formed.
→ 40Assertion (A): A spherical lens formula is given by 1/f = 1/v - 1/u. Reason (R): All distances for lenses are measured from the optical center.
→ 41What type of image is formed by a simple camera lens (which is typically a convex lens)?
→ 42Explain the phenomenon of lateral inversion with respect to a plane mirror.
→ 43A convex mirror is used as a security mirror in a shop. The owner observes a customer 5 m away, and her image appears to be 1/5th the actual size. Calculate the focal length of the mirror.
→ 44What is the absolute refractive index of a vacuum?
→ 45An incident ray passing through the focus of a convex lens will emerge how after refraction?
→ 46Assertion (A): When an object is placed at 2F of a convex lens, its image is formed at 2F on the other side. Reason (R): The magnification of the image formed when the object is at 2F is -1.
→ 47The power of a lens is +4.0 D. Is the lens thick or thin compared to a lens of power +2.0 D? Explain.
→ 48Which type of spherical mirror is used by dentists to see larger images of teeth?
→ 49A spherical mirror forms a real, inverted image of magnification -1. Where is the object placed relative to the mirror?
→ 50Why is the focal length of a concave mirror considered negative by convention?
→ 51An object is placed at a distance of 15 cm from a concave lens of focal length 10 cm. What is the nature of the image formed?
→ 52A light ray passes from a medium P to a medium Q. If the angle of incidence is 40° and the angle of refraction is 25°, which medium is optically denser?
→ 53Assertion (A): A ray passing through the optical center of a lens goes undeviated. Reason (R): The optical center is the midpoint of the lens.
→ 54What is the focal length of a plane mirror?
→ 55A ray of light traveling in a medium of refractive index n1 strikes the interface of a medium of refractive index n2. If n1 > n2, under what condition can total internal reflection occur?
→ 56Explain why a virtual image cannot be projected on a screen.
→ 57A convex lens of focal length 20 cm is placed in contact with a concave lens of focal length 25 cm. What is the nature of the combined lens system?
→ 58I will proceed to generate the rest of the questions carefully.An object is placed 30 cm from a concave mirror. If the focal length of the mirror is 10 cm, find the position of the image and its nature.
→ 59Let's use a numerical problem based on image formation properties and mirror formula. An object is placed 30 cm from a concave mirror. If the focal length of the mirror is 10 cm, find the position of the image and its nature.
→ 60An object is placed 60 cm from a screen. A convex lens is used to form a real image of the object on the screen. If the image is formed at a distance of 40 cm from the object, find the focal length of the lens.
→ 61Why is a real image always inverted, while a virtual image is always erect (for single mirror/lens setups)?
→ 62What is meant by the principal axis of a spherical mirror?
→ 63A light ray passes from a medium A to a medium B. If the angle of incidence is 45° and the angle of refraction is 30°, calculate the refractive index of medium B with respect to medium A. (sin 45° = 0.707, sin 30° = 0.5)
→ 64Why do convex lenses have a real focal point, while concave lenses have a virtual focal point?
→ 65Assertion (A): A magnifying glass uses a convex lens. Reason (R): A convex lens can form a virtual, magnified image.
→ 66An object is placed 10 cm from a convex mirror of focal length 15 cm. Calculate the position and nature of the image.
→ 67How does the speed of light change when it passes from a rarer medium to a denser medium? What effect does this have on its wavelength and frequency?
→ 68A ray of light incident normally on a plane mirror. What is the angle of reflection?
→ 69What is the relationship between the radius of curvature (R) and the focal length (f) of a spherical mirror?
→ 70A boy is trying to focus sunlight using a spherical mirror. At what position should he place the paper to get the sharpest image of the sun?
→ 71Assertion (A): It is difficult to read a newspaper through a sheet of clear glass placed on it. Reason (R): The refractive index of glass is different from that of air.
→ 72A pencil appears thicker and shorter when viewed from the side through a cylindrical glass of water. Explain this phenomenon.
→ 73An object is placed 10 cm in front of a concave mirror producing a real image 20 cm from the mirror. Calculate the focal length of the mirror.
→ 74Why are large parabolic mirrors used in solar furnaces?
→ 75A student holds a reading glass (convex lens) in the sun to burn a piece of paper. Where should the paper be placed relative to the lens?
→ 76If a convex lens is immersed in a liquid having a refractive index greater than that of the lens material, how will its focal length and nature change?
→ 77A plane mirror is rotated by an angle θ. By what angle does the reflected ray rotate?
→ 78An object is placed at a distance equal to twice the focal length (2F) of a convex lens. Describe the characteristics of the image formed.
→ 79Which of the following optical phenomena is responsible for the twinkling of stars?
→ 80Assertion (A): The power of a convex lens is positive. Reason (R): A convex lens is a converging lens and its focal length is positive.
→ 81Why does a convex mirror always produce a virtual, erect, and diminished image, regardless of the object's position?
→ 82A light ray travels from a medium X to a medium Y. The speed of light in X is 2.5 x 10⁸ m/s, and in Y it is 2.0 x 10⁸ m/s. What is the refractive index of medium Y with respect to medium X?
→ 83A student uses a concave mirror to project the image of a candle flame on a screen. If the image formed is inverted and three times the size of the flame, and the screen is 60 cm from the mirror, what is the object distance?
→ 84An object is placed at a distance of 10 cm from a plane mirror. If the object is moved 5 cm towards the mirror, how does the distance between the object and its image change?
→ 85A light ray passes through a rectangular glass slab. Explain why the emergent ray is parallel to the incident ray but is laterally displaced.
→ 86A doctor prescribes a corrective lens of power +2.0 D. Is this lens converging or diverging, and what is its focal length?
→ 87Why are silvered surfaces used in mirrors?
→ 88Two lenses, one convex with focal length +20 cm and another concave with focal length -10 cm, are placed in contact. What is the power of this combination?
→ 89Under what conditions will a convex lens form a virtual image? Draw a ray diagram to support your answer. (No drawing expected here, just descriptive answer.)
→ 90A ray of light is incident at an angle of 30° on a glass slab of refractive index 1.5. Calculate the angle of refraction. (sin 30° = 0.5)
→ 91A student performs an experiment with a convex lens and determines its focal length to be 10 cm. If an object is placed 8 cm from the lens, describe the characteristics of the image formed.
→ 92Assertion (A): The bottom of a tank filled with water appears raised. Reason (R): Light rays bend away from the normal when they travel from a denser medium to a rarer medium.
→ 93A person wishes to see a magnified image of an object using a spherical mirror. What type of mirror should they choose, and where should the object be placed?
→ 94Explain why a spoon appears bent when partially immersed in water.
→ 95Compare and contrast the image formation by a concave lens and a convex mirror when the object is placed at infinity.
→ 96Light enters from air into glass having refractive index 1.50. What is the speed of light in the glass? (Speed of light in vacuum is 3 x 10⁸ m/s).
→ 97A diverging lens is placed 15 cm from an object. If the image is formed 10 cm from the lens on the same side as the object, calculate the focal length and power of the lens.
→ 98An object of height 4 cm is placed 20 cm in front of a convex lens of focal length 12 cm. Find the position, nature, and height of the image.
→ 99The refractive index of diamond is 2.42. What is the meaning of this statement in relation to the speed of light?
→ 100A ray of light traveling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Explain your answer.
→ 101Assertion (A): A convex mirror is used as a rear-view mirror in vehicles. Reason (R): A convex mirror forms virtual, erect, and diminished images, and has a wider field of view.
→ 102Why does a concave mirror form a real image when an object is placed beyond its focal point (F), but a virtual image when the object is placed between the pole (P) and F?
→ 103New question for #2: An object is placed at 25 cm from a concave mirror of focal length 15 cm. What is the nature and magnification of the image formed?
→ 104Let's try a simpler one that leads to one of the options. A concave mirror has a focal length of 15 cm. At what distance should an object be placed from it so that it forms a real image at a distance of 30 cm from the mirror?
→ 105A concave mirror forms a real image of an object magnified 3 times. If the object is moved 10 cm towards the mirror, the image formed is still real and magnified 5 times. Calculate the focal length of the mirror.
→ 106A boy is standing 10 m in front of a plane mirror. If he walks 2 m towards the mirror, what is the new distance between the boy and his image?
→ 107We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object?
→ 108Which of the following lenses would you prefer to use while reading small letters found in a dictionary? (a) A convex lens of focal length 50 cm. (b) A concave lens of focal length 50 cm. (c) A convex lens of focal length 5 cm. (d) A concave lens of focal length 5 cm.
→ 109No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be (a) only plane. (b) only concave. (c) only convex. (d) either plane or convex.
→ 110Where should an object be placed in front of a convex lens to get a real image of the size of the object? (a) At the principal focus of the lens (b) At twice the focal length (c) At infinity (d) Between the optical centre of the lens and its principal focus.
→ 111The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object? (a) Between the principal focus and the centre of curvature (b) At the centre of curvature (c) Beyond the centre of curvature (d) Between the pole of the mirror and its principal focus.
→ 112Which one of the following materials cannot be used to make a lens? (a) Water (b) Glass (c) Plastic (d) Clay
→ 113Find the power of a concave lens of focal length 2 m.
→ 114A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
→ 115Define 1 dioptre of power of a lens.
→ 116The refractive index of diamond is 2.42. What is the meaning of this statement?
→ 117You are given kerosene, turpentine and water. In which of these does the light travel fastest?
→ 118Light enters from air into glass which has a refractive index of 1.50. If the speed of light in vacuum is 3 × 10⁸ meters per second, what is the speed of light in the glass?
→ 119A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
→ 120A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?
→ 121Find the focal length of a convex mirror whose radius of curvature is 32 cm.
→ 122Why do we prefer a convex mirror as a rear-view mirror in vehicles?
→ 123Name a mirror that can give an erect and enlarged image of an object.
→ 124The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
→ 125Define the principal focus of a concave mirror.
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