LIGHT-REFLECTION & REFRACTION

 

LIGHT-REFLECTION & REFRACTION

Light is a form of energy, which enable us to see the object. In this chapter we will study the phenomena of reflection and refraction using the property of light i.e., straight line propagation (Light wave travel from one point to another, along a straight line).

Reflection of Light

When the light is allowed to fall on highly polished surface, such as mirror, most of the light gets reflected.

Laws of Reflection

1. The angle of incidence is always equal to angle of reflection.

2. The incident ray, reflected ray and the normal to the reflecting surface at the point of incidence lie in the same plane.

Image formed by Plane Mirror (Plane reflecting surface)

1) Virtual (imaginary) & Erect (Virtual The image that do not form on screen.)

2) Laterally inverted (The left side of object appear on right side of image)

3) The size of image is equal to that of object

4) The image formed is as for behind the mirror as the object is in front of it.

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VOLTE

← Light-Reflection and Refraction

4) The image formed is as for behind the mirror as the object is in front of it. Reflection of light by spherical Mirrors

Mirrors, whose reflecting surface are curved inward or outward spherically are

called spherical mirror. For example - Spoon) The curved surface of shinning spoon can be considered

as curved mirror.

If it is curved inward - Act as concave mirror

If it is curved outward - Act as a convex mirror. Few Basic terms related to Spherical Mirror

1. Principal axis: Line joining the pole and centre of curvature of the spherical mirror.

2. Pole: The geometrical central point of the reflecting spherical surface. (aperture), denoted by (P).

3. Aperture: The width of reflecting spherical surface.

4. Centre of curvature: The reflecting surface of a spherical mirror forma part of sphere. It has a centre, which is known as centre of curvature, denoted by (C)

5. Radius of curvature: The separation between the pole and the centre of curvature, i.e., PC = R

6. Focus point: The point on the principal axis, where all parallel rays meet after reflection, denoted by (F)

7. Focal length: The length between the pole and focus point i.e., PF=f

Uses of Concave Mirror

1. Used in torches, search light and headlight of vehicle.

2. Used to see large image of face as shaving mirror

3. Used by dentist to see large images of the teeth

4. Large concave mirror used to focus sunlight (heat) in solar furnaces.

Uses of Convex Mirror

1. Used as rear-view mirror in vehicles because it gives erect image. It also helps the driver to view large area.

Sign Convention for Reflection by Spherical Mirror

1. The object is always placed to the left side of mirror.

2. All distance should be measured from pole (P); parallel to principal axis.

3. Take 'P' as origin. Distances measured

Right of the origin (+ x - Axis) are taken positive Left of the origin (-x-Axis) are taken negative

Perpendicular to and above principal axis (+y-Axis) are taken positive Perpendicular to and below principal axis (-y-Axis) are taken negative

MIRROR FORMULA

f-distance between F and Pole, v- distance of image from Pole, u-distance of object from Pole, R-distance between centre of curvature and pole.

wheref=

MAGNIFICATION

It is expressed as the ratio of the height of the image to height of the object

m= height of image h' height of object h

It is also related to 'u' and 'v'