CONCAVE AND CONVEX LENS, IDENTIFICATION AND RELATED TERMS

THE PHYSICS CAFE                                                                                    

CHAPTER TEN - LIGHT - REFLECTION AND REFRACTION

 

1.16 Spherical Lens and their Identification and Related terms**                                       

Spherical Lens: A curved and smooth piece of glass whose surfaces are curved. These are called curved lens due to their shape is curved.

 

Hint: The surfaces are curved to bend the light when passes through it.

 

Types and Identification

Types of spherical lens: Two (according to syllabus)

1. Concave lens: If incident ray enter into cave like surface.

1. Convex lens: If incident ray don’t enter into cave like surface.

Hint: If light ray falls normally (Perpendicularly) to lens it does not bend and passes straight through the lens.

To see video proof click on the link

Concave lens spreads the incident parallel light rays so called diverging lens

Convex lens concentrate the incident parallel light rays so called converging lens

Related terms**:

Centre of curvature (C): The centre of the hollow sphere of glass from which the piece if glass is taken for making lens.

 

Focus (F): The point where all the parallel light rays to principal axis, meet after refraction by lens.

 

Optical centre (O): The centre of lens.

 

Principle axis: An imaginary line which passing through the centre of curvature and optical centre of lens.

 

Radius of curvature (R): Distance between the optical centre and centre of curvature.

 

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

f = R / 2

Aperture: It is the diameter of the spherical lens.

 

 

1.17 Rules for Image Formation and Terms Related About Images**                                    

 

Rules for Image Formation:

 

1. Always place the object left side of lens.

 

2. Take two light rays from the head of object. One parallel to principal axis and second incident at optical centre.

 

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

 

4. Incident light ray falling at optical centre will always refract in the direction of incident light ray (without bending).

 

 

 

Terms Related About Images:

 

5. Image will be formed at the point where both the refracted light ray meets. The distance of this point from optical centre is called Position of image

 

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

 

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

  

8. Size of the image is told as compared to object’s size, like image formed is point sized, small sized, same sized, large sized, very large sized as compared to object’s size.

 

Hint:

Real Image: Real image formed where refracted light ray actually meets

Virtual Image: Virtual image formed where backside extended refracted light rays meets.

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