Light reflection and refraction Worksheet-8

Light reflection and refraction Worksheet-8

1. The refractive index of glycerin is 1.46. What is the speed of light in air if its speed in glycerin  is 2.05 × 10⁸ m/s ?

2. The refractive index of glass is 1.6 and that of diamond is 2.4. Calculate refractive index of diamond with respect to glass.

3. The refractive index of glass is 1.6 and that of diamond is 2.4. What is the refractive index of glass w.r.t. diamond ?

4. A ray of light is traveling from glass to air. The angle of incidence in glass is 35°, and angle of refraction in air is 60°. What is the refractive index of glass w.r.t. air ?

5. A ray of light is traveling from air to water. What is the angle of incidence in air, if angle of refraction in water is 41° ? Take refractive index of water = 1.32.

6. The image obtained with a convex lens is erect and its length is 4 times the length of the object. If the focal length of the lens is 20 cm, calculate the object and image distances.

7. A needle placed 45 cm from a lens forms an image on the screen placed 90 cm on the other side of the lens. Identify the type of the lens and determine its focal length.  What is the size of the image if the size of needle is 5.0 cm ?

8. The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose ?

9. Calculate the distance at which an object should be placed in front of convex lens of focal length 10 cm to obtain an image of double its size.

10. The image of a needle placed 10 cm from a lens is formed on a wall 20 cm on the other side of the lens. Find focal length of the lens and size of image, formed, if the size of object needle is  2.5 cm.

Answer:

1. Here, 

From   

              = 2.99 × 10⁸ m/s.

2. = 1.5

4. Here, i = 35°, r = 60°,  ^an_g = ?

From

5. Here,  i = ?, r = 41°,   ^an_w = 1.32

From  

Using tables of natural sines; I = 60°

6. Here,   

              f = 20 cm,     u = ?,      v = ?

As          

          u = –15 cm

          v = 4u = 4(–15) = –60 cm.

7. Here,

From

          f = 30 cm

As f is positive, the lens must be convex.

From  

As h₂ is negative, the image is inverted.

8. Here, distance between the object and image

          u + v = 3 m.

focal length of lens, f = ?

As maximum distance between an object and image in case of convex lens = 4 f

∴ 4 f = 3 metre

          = 0.75m.

9. Here, f = 10 cm, object distance, u = ?

In a convex lens, the image can be real as well as virtual.

∴ magnification,

As    

∴    

or     

or     

∴     u = –5 cm

∴     u = –15 cm         

10. Here,   u = –10 cm,    v = 20 cm,    f = ?

As    

          6.67 cm.

Also,

          h₂ = –5 cm. As h₂ is negative is inverted.