Top 10 Notes, 10th Sci.1, 7. lenses... 🎷

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🦅 Definition of lens

A transparent medium that focuses / converges or disperses / diverge light rays which bound by two surfaces through refraction.

Different types of lenses are present.

There are three types of convex lenses , 

Biconvex , 

Plano convex , 

positive meniscus ,

There are three types of concave lens present. 

Biconcave , 

Plano concave and 

negative meniscus.

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💫 Uses of lens

A. Spectacles

B. Watch repairing

C. Telescope and microscope

D. In the front door of the house.

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🎷Convex lens

1. Definition of convex lens :-The lens which has two spherical surfaces which are puffed outwards is called convex lens.

2.. The convex lens is thicker near the centre as compared to the edges.

3. By convex lens we get two types of images real and virtual.

4. By the convex lens we get pointed , smaller , same size , larger , very large image means we get all types of images.

5. The focal length (f) of the convex lens is positive +ve .

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🥁 1. Definition of Concave lens :- The lens with both surfaces spherical on the inside is called a concave lens.( surface that curves inward).

2. Concave lens is thinner at the centre as compared to its edges.

3. By concave lens we get only virtual image.

4. By concave lens we get only two types of images pointed or small.

5. The focal length of concave lens is negative -ve.

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Now It is very easy to write the difference between convex and concave lens from above point.

 Definition Refraction of light

When a light rays goes from one transparent medium to another transparent medium they change in their direction this change in direction is called refraction of light.

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💐 A Ray of light gets refracted twice in passing through a lens. The direction of rays changes because of refractions.

Now we will see some definitions related to the lens.

A. Centre of curvature C. A lens which is part of Circle it's center is called center of curvature.

B. Radius of curvature R : A lens which is part of a circle its radius is called radius of curvature.

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C. Principal axis :- The imaginary line passing through both centre of curvature is called the principle axis. The imaginary line which passes through the centre of the curvature C and optical centre O is called principal axis. 

D. Optical centre O :- The centre point of lens which is on the principal axis through which the rays of light pass without any deflection / deviation.

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E. Principle focus F :- 

1. Principal focus of convex lens:- the rays of light parallel to the principal axis after refraction get concentrated on a principal axis that point is called as principal focus of convex lens.

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2. Principal focus of concave lens:- 

The rays of light parallel to the principal axis after refraction appear to be diverged from a point which is on the principle axis it's called the principle focus of the concave lens.

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F. Focal length f :- The distance between the optical centre and principal focus is called focal length.

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 🌈 Write rules for obtaining an image formed by a convex lens.

1. The Ray of light which is parallel to the principal Axis after refraction goes through the principle focus.

2. The Ray of light which goes through the principal focus after refraction is parallel to the principal axis.

3. The Ray of light which goes through the optical centre goes straight.

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🥁 Six 6 Image formation by a convex lens lens for different positions of the object.

1. Position of the object :- at infinity

@ Position of the image :- at focus F.

Size of the image :- pointed image

Nature of the image :- real and inverted.

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2. Position of the object :- beyond 2F1 .

position of the image :- between F2 and 2F2 .

size of the image :- smaller than an object .

nature of the image :- real and inverted.

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3. The position of the object :- at 2F1 .

position of the image :- at 2F2 . size of the image :- same size .

nature of the image :- real and inverted.

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4. Position of the object :- between F1 and 2F1 . 

position of the image :- beyond 2F2 . 

size of the image :- larger than the object . nature of the image :- real and inverted.

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5. The position of the object :- at the focus F1 .

position of the image :- at the infinity .

 size of the image :- very large .

 nature of the image :- real and inverted .

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6. Position of the object :- between F1 and optical centre O.

Position of the image :- on the same side of the lens as the object. size of the image :- very large .

 Nature of the image :- virtual and Erect .

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