PHYSICS 10TH

THE PHYSICS CAFE                                                   

CHAPTER TEN

LIGHT - REFLECTION AND REFRACTION

 

1.05 Spherical Mirror and their Identification and Related terms**                                      1

Spherical Mirror: A curved and smooth piece of glass which is silver metal polished from one side. These are also called curved mirror due to their shape is curved.

 

Hint: For this type of mirror the piece of glass is cut from hollow sphere of glass.

 

Types and Identification

Types of spherical mirrors: Two

1. Concave mirror: If reflecting surface is toward the center of curvature or if incident ray enter into cave like reflecting surface and polished surface is other side.
2. Convex mirror: If reflecting surface is other side of center of curvature.

Hollow Sphere of glass: A sphere made up of glass and empty from inside like football.

 

Reflecting surface: The front side of the mirror at this surface reflection takes places.

 

Polished surface: The back side of the mirror at this surface polish is done

 

Center of curvature (C): The center of the hollow sphere of glass from which the piece if glass is taken for making mirror.

 

Focus (F): The point where all the parallel light rays to principle axis, meet after reflection by mirror.

 

Pole (P): The center of piece of glass which is used for making mirrors.

 

Principle axis: An imaginary line passing through the center of curvature and the pole.

 

Radius of curvature (R): Distance between the pole and center of curvature.

 

Focal length (f): It is the half of distance between the pole and center of curvature.

f = R / 2

Aperture: It is the diameter of the spherical mirror.

 

1.06     Rules for Image Formation and Terms Related About Images**                            1

 

Rules for Image Formation:

 

1. Always face the mirror towards left side.

 

2. Always place the object left side of mirror.

 

3. Take two light rays from the head of object. One parallel to principal axis and second incident at pole.

 

4. Incident light ray parallel to principal axis will always pass through focus.

5. Incident light ray parallel at pole will always reflected at the angle equal to incidence angle.

 

Hint: to draw reflected ray, place a point just below the image at a distance equal to height of the object as shown in figure by red color. Now pass the reflected light ray from this point.

 

Terms Related About Images:

 

6. Image will be formed at the point where both the reflected light ray meets. This is called Position of image

 

7. If both reflected light ray meets actually then the image formed will be Real image and if both reflected light ray don’t meet actually then extend them backside of mirror then the image will be formed at the point where extended rays meet and this type of image is called Virtual image.

 

8. Hint: The arrow head represents the head of the object/image and foot will always lie on principle axis.

9. Size of the image is told as compared to object like image formed is point sized, small sized, equal, large sized, very large sized.

 

Hint:

Real Image: Real image will be in front of the mirror, that why we can touch it because reflected light ray actually meets there and can see it on screen (screen means it can be any white color smooth material)

Virtual Image: Virtual image will be in back side of the mirror, that why we can touch it because reflected light ray don’t cross the mirror and can see it on screen.