By: Aries Triwidajati Soenoko Smp Negeri 2 Cileunyi

Lens By : Aries Triwidajati Soenoko SMP Negeri 2 Cileunyi

Basic Competence Investigate the characteristic of light and the relation with mirror and lens

Learning Objectives After this lesson, student are able to : 2. Drawing of an image through a ruler in the Lens 3. Mention the characteristics of an image in the Lens 4. Calculate focus, object, image, and magnification positions.

Lens

Lens ..……….....? Lens is a portion of a transparent refracting medium bounded by two surfaces which are generally spherical or cylindrical or one curved and one plane surface.  

the lenses are classified as

 

1. convex lens or converging lens   2. concave or diverging lens  

Convex Lens

Convex Lens is a lens which is thicker in the middle and thinner at the edges

The convex lenses shape are classified as : 1. bi-convex or double convex   2. convex - plane   3. convex - concave  

The convex lenses shapes

Concave Lens

Concave Lens is a lens which is thinner at the middle and thicker at The concave lenses shape are classified as : the edges 1. bi-concave   2. concave - plane 3. concave - convex  

The concave lenses shapes

Formation of Image by a Convex Lens A ray of light passing through the optical center of the lens travels straight without suffering any deviation. This holds good only in the case of a

An incident ray parallel to the principal axis after refraction passes through the focus.

An incident ray passing through the focus of a lens emerge parallel to the principal axis after refraction.

Example Image is formed When the Object is Placed Between F1 and O

1. 2. 3. 4.

Formed on the same side of the lens virtual erect magnified

When the Object is placed at 2F1

The image are: 2. formed at 2F2 3. real 4. inverted 5. same size as the object

The table below gives at a glance the position, size and nature of the image formed by a convex lens corresponding to the different positions of

Like in the mirror, an equation can also be used to located the image and find its size in the lens. The focal length (f) the distance of the object from the lens (S0) and the distance of the image from the lens (Si) are related by the mirror equation :

The ratio of the size of the image (hi) to the size of the object (h0) is called the magnification (m). The magnification is related to the distances to the mirror by equation :

If Si and S0 positive, the both m and hi are negative. This means that the image is inverted.

Review 1. A concave mirror has a radius of curvature of 60 cm. Calculate the image position and magnification of an object placed in front of the mirror at distances of (a) 90 cm and (b) 20 cm. (c) Draw ray diagrams to obtain the image in each case. 2. Calculate the image position and magnification for an object placed (a) 20 cm and (b) 60 cm in front of a convex mirror of focal length 40 cm. (c) Use ray diagrams to locate image positions corresponding to the object positions in (a) and (b).

Orang bisa karena biasa, orang biasa karena dipaksa dan karena dipaksa orang bisa

Good 21