Light reflection and refraction Worksheet-15

Light reflection and refraction Worksheet-15

 

  1. The image of a distant object is formed at 30 cm from a concave mirror. What is the focal length of the mirror ?

 

  1. The radius of curvature of concave mirror is 50 cm. Where should an object be held from the mirror so as to form its image at infinity ?

 

  1. A man standing in front of a special mirror finds his image having a small face, big tummy and legs of normal size. What are the shapes of three parts of the mirror ?

 

  1. On what factors does the focal length of a spherical mirror depend ?

 

  1. Can you change focal length of a given spherical mirror by changing the object distance from the mirror?

 

  1. Can you change linear magnification of a spherical mirror by changing the object distance from the mirror ?

 

  1. For the same angle of incidence in media P, Q and R, the angles of refraction are 35°, 25°, 15° respectively. In which medium will the velocity of light be minimum?

 

  1. What is the basic cause of refraction ?

 

  1. A ray of light traveling in air is incident on a rectangular glass slab. What will happen?

 

  1. If refractive index of glass w.r.t air is 3/2, what is the refractive index of air w.r.t. glass ?

 

Answer:

  1. As image of a distant object is formed at the principal focus of the mirror, therefore, focal length of the mirror is 30 cm.

 

  1. Here, R = 50 cm, = 25 cm. The object held at focus, i.e., at 25 cm from the mirror will have its image at infinity.

 

  1. The upper part of mirror showing smaller face must be convex.

The middle part of the mirror showing big tummy must be concave.

The lower part of mirror showing normal legs must be plane.

 

  1. Focal length of a spherical mirror depends on radius of curvature of the mirror.

 

  1. No, we cannot change focal length of a spherical mirror by changing the object distance (u). By changing u ; will change, but  f  will remain the same.

 

  1. Yes, magnification of a concave mirror is different in different positions of the object or  m can be changed by changing the object distance.

 

  1. According to Snell's law,

Also,

For given angle of incidence (i), v will be minimum, when angle of refraction r  is minimum, which is for medium R. 

 

  1. The basic cause of refraction is the change in the speed of light in going from one medium to the other.

 

  1. In passing through a rectangular glass slab, a ray of light undergoes two refractions and emerges from opposite side of the slab in a direction parallel to the direction of incidence of light. And the emergent ray is displaced laterally.

 

  1. ang 3/2,  gna = ?