Light reflection and refraction Worksheet-18

Light reflection and refraction Worksheet-18

1. A convex lens of focal length 20 cm is placed in contact with a concave lens of focal length 10 cm. What is the focal length and power of the combination?

2. If the magnification of a body of size 1 m is 2, what is the size of the image ?

3. What is the power of a concave lens of focal length 25 cm ?

4. What will be the focal length of a lens whose power is given as + 2.0 D ?

5. Where will the image be formed by a concave mirror when an object is placed between the pole and the focus point of the mirror ?

6. What is the value of focal length of a plane mirror?

7. A ray of light is incident on a convex mirror as shown in the image

Redraw the  diagram after completing the path of the light ray after reflection from the mirror.

8. Show the direction of the light ray after reflection.

9. The refractive index of diamond is 2.42. What is the meaning of this statement in relation to speed of light?

10. Show the formation of image of the object AB with the help of suitable rays.

Answer:

1. Here, f₁ = +20 cm,  f₂ = –10 cm; F = 7, P = ?

From

          F = -20cm.

          P =   diopter.

2. Here, m = 2, h₁ = 1 m, h₂ = ?

As    

∴     h₂ = m h₁ = 2 × 1 = 2m.

3. Here, P = ? f = –25 cm

As     P =

∴     dioptre .

4. Here f  = ?, P = + 2.0 D

As            ∴ 50 cm.

5. At the back of concave mirror and it will be virtual, erect and magnified.

6. The focal length of a plane mirror is infinity.

7. The complete path of light ray

The ray is reflected from the mirror and appears to come from focus F of the mirror.

8. As the ray is passing through principal focus  F of concave mirror, on reflection, it would become parallel to the principal axis of the mirror

This is the speed of light in diamond.

10. The course of rays for the formation of image of object AB is shown in the. The image A'B' is virtual, erect and magnified.