Light reflection and refraction Worksheet-10

Light reflection and refraction Worksheet-10


  1. A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it Where is the image located ?


  1. A ray of light traveling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal ?  Give Reason.


  1. Light enters from air to glass having refractive index 1.5. What is the speed of light in glass ? The speed of light in vacuum is 3 × 108 m/s.


  1. The refractive index of diamond is 2.42. What is the meaning of this statement ?


  1. Define one dioptre of power of a lens.


  1. A 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 size of the object ? Also, find the power of the lens.


  1. Find the power of a concave lens of focal length 2 m.


  1. 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.


  1. Name the type of mirror used in the following situation :

Head lights of a car.

Support your answer with reason.


  1. Name the type of mirror used in the following situation also give reason:

Side rear view mirror of a vehicle.



  1. Here, linear magnification, u = –3 (negative sign for real image, which is inverted)

object distance, u = –10 cm

image distance, v = ?


The image is located at 30 cm in front of the mirror.


  1. When a ray of light travels from air into water obliquely, it bends towards the normal. This is because water is optically denser than air. On entering water, speed of light decreases and the light bends towards normal.


  1. Here, refractive index  n = 1.5, speed of light in vacuum c = 3 × 108 m/s

speed of light in glass, v = ?



  1. Refractive index of diamond is the largest (= 2.42).

Therefore, optical density of diamond is the largest. As therefore . As n is the largest, v is the smallest, i.e., velocity of light in diamond is minimum.


  1. One dioptre is the power of a lens of focal length 1 metre.


  1. Here, the image distance, v = 50 cm

          Object distance, u = ?

          Power of lens, P = ?

As the image is of the same size as the object, therefore, object must be at a distance equal to twice the focal length of the lens. In this case,

          –u =  v = 2f = 50 cm.

∴     u = –50 cm and f = 25 cm.

As     P = ∴ P = = 4 dioptre.


  1. Here, Power,  p = ?,  focal length, f = –2 m = –200 cm


–0.5 dioptre.


  1. To obtain an erect image of an object in a concave mirror, the object is placed between pole and principal focus of the mirror.

Therefore, range of distance of the object from the mirror must be less than 15 cm.

 The image will be erect and virtual. The size of image would be larger than the size of the object. 


  1. For head lights of a car, we use a concave mirror. The light source is held at the focus of the mirror. On reflection, a strong parallel beam of light emerges.


  1. A convex mirror is used as side rear view mirror, because its field of view is larger, and it forms virtual, erect and diminished images of objects behind.