Image formation by covex and concave lenses

 

IMAGE FORMATION BY CONVEX LENS (6 CASES)

When object is at

1)1)  Infinity:

Applying rule1

Nature: Image formed is real, inverted (the rays below principal axis go above principal axis and rays above principal axis go below principal axis after reflection), highly diminished and forms at F.

This application is used in solar cookers.

1)  2)  Beyond C:

Applying rule1 and rule2

Nature: Image formed is real, inverted, diminished and forms between C and F.  

3)    At C:

Applying rule1 and rule2

Nature: Image formed is real, inverted, same size and forms at C.

4)    Between C and F:

Applying rule1 and rule2

Nature: Image formed is real, inverted, enlarged and forms behind C.

5)    At F:

Applying rule1 and rule3

Nature: Image formed is real, inverted, highly enlarged and assumed to be   forms at infinity.

6)    Between F and P:

Applying rule1 and rule2

Nature: Image formed is virtual, erect, enlarged and forms at same side of the lens.

This case6 of the convex lens is used by some doctors (like Dentists and E.N.T specialists) to see the image of the object with enlarged size.

IMAGE FORMATION BY CONCAVE LENS (2 CASES)

Object is kept at

1                 1) At infinity:

Applying rule1

Nature: Image formed is virtual, erect, highly diminished and forms at F.

1        2) Anywhere between infinity and optic centre: 

Applying rule1 and rule3

Nature: Image formed is virtual, erect, diminished and forms between P and F. Here image will be shifted between F and P depending upon the object distance.

This case2 of concave lens is the application of spy hole lens fixed to main doors of our houses. This lens reduces the size of the virtual image and can show wide area.

How to show the formation of image when a parallel beam of rays falls on the lens by making certain angle with principal axis?

Convex lens:

See the solved figure below

We use simple steps to show the image formation like above

Step 1: Draw a dotted line perpendicular to principal axis at F1. This is         called focal plane.

Step 2: extend a ray passing through optic centre (un deviated ray) until it cuts at a point on focal plane.

Step 3: Join all the remaining rays to this point. That’s it here is a point size image formed on focal plane.

Concave lens:

see the solved figure below

Step 1: Draw focal plane at F1. And locate a point where a ray passing through optic centre is meeting the focal plane.

Step 2: join this point on the focal plane with all the points of incidence on the lens with virtual rays (dotted lines).

Step 3: now extend these virtual rays on the other side of the lens to get a diverged beam of rays. (the image we got is at the point on focal plane where all virtual rays are meeting)

                        thank you