Light -Reflection and Refraction

A plane mirror is a mirror with a flat (planar) reflective surface.[1][2] For light rays striking a plane mirror, the angle of reflection equals the angle of incidence.[3] The angle of the incidence is the angle between the incident ray and the surface normal (an imaginary line perpendicular to the surface). Therefore, the angle of reflection is the angle between the reflected ray and the normal and a collimated beam of light does not spread out after reflection from a plane mirror, except for diffraction effects.

A plane mirror makes an image of objects in front of the mirror; these images appear to be behind the plane in which the mirror lies. A straight line drawn from part of an object to the corresponding part of its image makes a right angle with, and is bisected by, the surface of the plane mirror. The image formed by a plane mirror is always virtual (meaning that the light rays do not actually come from the image), upright, and of the same shape and size as the object it is reflecting. A virtual image is a copy of an object formed at the location from which the light rays appear to come. Actually, the image formed in the mirror is a perverted image (Perversion), there is a misconception among people about having confused with perverted and laterally-inverted image. If a person is reflected in a plane mirror, the image of his right hand appears to be the left hand of the image.

Angle of glancing is the angle made by incident ray with the reflecting surface.

Angle of deviation is the angle between original path of light ray and its final direction.

In this video i have taken  numericals on  two plane inclined mirrors . Calculating angle of deviation . This is one of the best problem based on calculating angle of deviation in two plane mirrors inclined to each other.

Plane mirrors produce images with a number of distinguishable characteristics.

Images formed by plane mirrors are virtual, upright, left-right reversed, the same distance from the mirror as the object's distance, and the same size as the object.

A curved mirror is a mirror with a curved reflecting surface. The surface may be either convex (bulging outward) or concave (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices.

A convex mirror or diverging mirror is a curved mirror in which the reflective surface bulges towards the light source.[1] Convex mirrors reflect light outwards, therefore they are not used to focus light. Such mirrors always form a virtual image, since the focal point (F) and the centre of curvature (2F) are both imaginary points "inside" the mirror, that cannot be reached. As a result, images formed by these mirrors cannot be projected on a screen, since the image is inside the mirror. The image is smaller than the object, but gets larger as the object approaches the mirror.

A concave mirror, or converging mirror, has a reflecting surface that is recessed inward (away from the incident light). Concave mirrors reflect light inward to one focal point. They are used to focus light. Unlike convex mirrors, concave mirrors show different image types depending on the distance between the object and the mirror.

These mirrors are called "converging mirrors" because they tend to collect light that falls on them, refocusing parallel incoming rays toward a focus. This is because the light is reflected at different angles at different spots on the mirror as the normal to the mirror surface differs at each spot.

1. Centre of curvature (C): Centre of the sphere of which the mirror is a part.

2. Radius of curvature (R): Radius of the sphere of which the mirror is a part.

3. Pole (P/O): Geometric centre of the spherical surface of the mirror.

4. Principal axis: Straight line joining the pole of the mirror to its centre of curvature.

Rules for drawing Ray Diagram in Lenses

• Rule 1 - Ray parallel to principal axis will pass through focus. For a convex lens , ...

• Rule 2 - Ray passing through focus will become parallel to principal axis. For a convex lens, ...

• Rule 3 - Ray passing through Optical Center will emerge without deviation.

Have you ever used a pair of binoculars to observe objects that are far away?

The size of the objects seen through the binoculars is not the same as what we see with our naked eyes. The binoculars focus the light from distant objects and help us to view the object in greater detail by making them appear bigger.

Mirror Formula and Magnification

The mirror formula is represented by the following equation:

1/f=1/v+1/u

Where f is the focal length of the mirror, uu the object distance is the distance of the object from the mirror and vv the image distance is the distance the image is formed from the mirror. This formula is valid in all situations, for all kind of spherical mirrors and for all positions of the object.

Using this equation to solve for uu and vv allows us to determine the magnification (mm ) of the object using the equation below.

m=−v/u     

The size of the image as compared to the object is related to the magnification. The size of an object’s image is larger (or smaller) than the object itself by its magnification, m.m. The level of magnification is proportional to the ratio of vv and u.u. An image that appears to be double the size of the actual object would have magnification m=2.m=2.

The radius of curvature of a mirror is twice its focal length.

R=2f       

We need to apply the new Cartesian Sign Convention while putting the values of u,vu,v and ff into the mirror formula.

All distances measured to the right of the origin (along positive x-axis) are taken as positive while those measured to the left of the origin (along negative x-axis) are taken as negative.

Cause of refraction is the change in the speed of light when light travels from one medium to another

Snell's law (also known as Snell–Descartes law and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.

In optics, the law is used in ray tracing to compute the angles of incidence or refraction, and in experimental optics to find the refractive index of a material. The law is also satisfied in metamaterials, which allow light to be bent "backward" at a negative angle of refraction with a negative refractive index.

Snell's law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction:

Sin i/ sin r = n2/ n1 = v1/ v2

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In optics, the refractive index (also known as refraction index or index of refraction) of a material is a dimensionless number that describes how fast light travels through the material. It is defined as

n=c/v

where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times slower in water than in a vacuum. Increasing the refractive index corresponds to decreasing the speed of light in the material.