Light – Reflection and Refraction: Class 10 Science Q&A · Page 2
47 free answers on Light – Reflection and Refraction (Science) for Class 10 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- ScienceClass 10CBSE
1. Under which of the following conditions a concave mirror can form an image larger than the actual object? (a) When the object is kept at a distance equal to its radius of curvature (b) When object is kept at a distance less than its focal length (c) When object is placed between the focus and centre of curvature When object is kept at a distance greater than its radius of curvature
Soln: Answer is (c) When object is placed between the focus and centre of curvature Explanation: When object is placed between F and C an enlarged image is formed beyond C.
- ScienceClass 10CBSE
1. A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is (a) – 30 cm (b) – 20 cm (c) – 40 cm – 60 cm
Soln: Answer is (b) – 20 cm Explanation: Here, size of object = O = + 10.0 mm = + 1.0 cm (as, 1 cm = 10 mm) Size of Image size = I = 5.0 mm = 0.5 cm Image distance, v = − 30 cm (as image is real) Let, object distance = u Focal length, f =? Magnification m= I (Size of image) O(Size of image) Magnification is given by m=−𝑣 𝑢 𝐼 = −𝑣 𝑂 𝑢
- ScienceClass 10CBSE
1. Which of the following can make a parallel beam of light when light from a point source is incident on it? (a) Concave mirror as well as convex lens (b) Convex mirror as well as concave lens (c) Two plane mirrors placed at 90° to each other Concave mirror as well as concave lens
Soln: Answer is (a) Concave mirror as well as convex lens Explanation: Emergent beams are parallel and the image is produced at infinity when light rays from a point source are incident on a concave mirror and convex lens.
- ScienceClass 10CBSE
A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Answer- Power of lens (P) = 1/f P = 1.5D f = 1/1.5 = 10/15 = 0.66 m A convex lens has a positive focal length. Therefore, it is a convex lens or a converging lens.
- ScienceClass 10CBSE
Find the focal length of a lens of power -2.0 D. What type of lens is this?
Answer- Power of lens (P) = 1/f P = -2D f = -1/2 = -0.5 m A concave lens has a negative focal length. Therefore, it is a concave lens.
- ScienceClass 10CBSE
The magnification produced by a plane mirror is +1. What does this mean?
The positive sign means an image formed by a plane mirror is virtual and erect. Since the magnification is 1, it means that the size of the image is equal to the size of the object.
- ScienceClass 10CBSE
One-half of a convex lens is covered with black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
Answer- Yes, it will produce a complete image of the object, as shown in the figure. This can be verified experimentally by observing the image of a distant object, like a tree on a screen, when the lower half of the lens is covered with black paper. However, the intensity or brightness of the image will reduce.
- ScienceClass 10CBSE
Name the type of mirror used in the following situations. (a) Headlights of a car (b) Side/rear-view mirror of a vehicle (c) Solar furnace Support your answer with a reason.
(a) Concave Mirror: Concave mirrors can produce a powerful parallel beam of light when the light source is placed at their principal focus. (b) Convex Mirror: Because of its largest field of view. (c) Concave Mirror: Because it concentrates the parallel rays of the sun at a principal focus.
- ScienceClass 10CBSE
We 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? Draw a ray diagram to show the image formation in this case.
Answer- Range of the distance of the object = 0 to 15 cm from the pole of the mirror. Nature of the image = virtual, erect, and larger than the object.
- ScienceClass 10CBSE
Which 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
Answer – (c) A convex lens of focal length 5 cm can be used while reading small letters found in a dictionary
- ScienceClass 10CBSE
No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be (a) plane (b) concave (c) convex (d) either plane or convex
Answer – (d) The mirrors are likely to be either plane or convex
- ScienceClass 10CBSE
A spherical mirror and a thin spherical lens have a focal length of -15 cm. The mirror and the lens are likely to be (a) both concave (b) both convex (c) the mirror is concave, and the lens is convex (d) the mirror is convex, but the lens is concave
Answer – (a) Both are likely to be concave.
- ScienceClass 10CBSE
Where 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.
Answer – (b) The object should be placed at twice the focal length
- ScienceClass 10CBSE
The 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.
(d) The position of the object should be between the pole of the mirror and its principal focus.
- ScienceClass 10CBSE
Which one of the following materials cannot be used to make a lens? (a) Water (b) Glass (c) Plastic (d) Clay
Answer – (d) Clay cannot be used to make a lens because if the lens is made up of clay, the light rays cannot pass through it
- ScienceClass 10CBSE
Find the power of a concave lens of focal length 2 m.
The focal length of the concave lens (f) = 2 m Power of lens (P) = 1/f = 1/ (-2) = -0.5D
- ScienceClass 10CBSE
Define 1 dioptre of power of a lens.
Dioptre is the SI unit of power of lens is denoted by the letter D. 1 dioptre can be defined as the power of a lens of focal length 1 metre.
- ScienceClass 10CBSE
The refractive index of diamond is 2.42. What is the meaning of this statement?
A diamond has a refractive index of 2.42, which means that the speed of light in a diamond will reduce by a factor of 2.42 as compared to its speed in the air. In other words, the speed of light in a diamond is 1/2.42 times the speed of light in a vacuum.
- ScienceClass 10CBSE
You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in the table.
Material medium Refractive index Material medium Refractive index Air 1.0003 Canada Balsam 1.53 Ice </td
- ScienceClass 10CBSE
Find out, from the table, the medium having the highest optical density. Also, find the medium with the lowest optical density.
Material medium Refractive index Material medium Refractive index Air 1.0003 Canada Balsam 1.53 Ice </td