# What is Light?

With reference to classical wave theory, the light is an electromagnetic wave, which can travel through free space under various magnetic and electrical fields or through a material medium.

The wave flows straight in the absence of impact. Electromagnetic radiation, such as light, is, in terms of contemporary quantum theory, streaming of photons into space (‘small parquets of light’).

Light, thus, consists of photons. As light appears on the earth, like a slice of glass, the part is projected and partially reflected. This occurs on any surface that forms the boundary of different refractive indices between two transparent media.

Light reflections are the sudden change in light distribution direction, which influences the frontier of various media. Light reflects.

## Terms used:

Energy from a single point source is a beam of light (usually depicted in diagrams by a long direct arrow.

Ray of incidence is a light ray striking a wall.

Reflected beam is a surface ray of light.

Standard is a perpendicular imaginary line to an area where reflection is taking place.

Incidence angle I is the angle of the incidence ray to the normal angle.

Reflection angle (r) is the angle of the reflected ray from the normal.

## First law:

The event light, the mirrored light and the natural ray are on the surface of the same axis.

## Second law:

The incidence angle is the same as the mirror angle.

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Regular Reflection

• Normal reflection refers to rays that come from a smooth surface.
• Parallel mirrored rays are present in any incident ray.

Diffused Reflections (irregular)

• Represents radiation arising from raw materials •
• Radiation expressed is not in the same direction
• The rules of reflection are, therefore, obeyed at any point of the rough surface.

## Refraction of Light

Light refraction requires the change in direction of the transition from one optically translucent medium to another (bending of light rays).

Refraction Terms Used:

• The bent ray is the refracted ray when switching from one optical medium to another.
• Standard is an imaginary line perpendicular to the screen interface where refraction takes place.
• The incidence angle is the angle of the incident ray to the usual angle.
• Refractive angle is the angle between the refracted and regular rays.

## Law Of Refraction:

The first rule notes that the incident light, the light refracted and the interface usual are all located on the same level.

Second refractive law sets the ratio sinisinr = constant, where ii is the incidence angle and rr is the refractive angle for the two given mediums.

n = sinisinrn = sinisinr refractive index(n) of a medium

The larger the magnitude of a medium’s refractive index, the greater the “bending” effect from air to that medium.

An optically denser medium is a substance with a greater value of n.

A material with a larger value of n is an optically denser medium.

In summary, light traveling from:

denser medium to less dense medium – Bend away from normal

less dense medium to denser medium – Bend towards normal

However, if the light ray enters another medium perpendicularly to the boundary, there is no deviation of the ray even when there is a change in the speed of light.

## Another definition for refractive index:

The medium’s refractive index (n) is the vacuum velocity ratio (c) for that medium to light velocity ( v). N may then be determined by:

n = cvn = cv

This means that the higher the medium’s refractive index, the slower the speed of light. This implies that the optical density of a medium increases with the rising refractive index.

## A consequence of refraction of light: Apparent Depth

A pool of water looks shallower than it really is. A straight object placed in water looks bent at the surfaces.

## Refractive Index & Wavelength of Light

For visible light, the refractive indexes of most transparent medium decrease with increasing wavelength. Hence,

1<n(λred)<n(λgreen)<n(λblue)1<n(λred)<n(λgreen)<n(λblue)

This causes white light to split in its constituent colors (rainbow) when it passes through a prism.

# Speed of Light Medium:

Currently, the medium does not slow down light. ALWAYS c is the speed of light. In Einstein’s theory of special relativity, this constant speed of light plays a crucial role. The light vels used in the above equation are simply the visible velocity of light in the above medium. (In reality it is incorporated into current physics theories). As light travels through a medium, the electrons in the air molecules are continuously absorbed and re-emitted. However, light reemission is not as immediate as the “action” of the electron with light for a brief time before the light is reemitted. This triggers the evident slower light pace.

# Diagrams of Plane Mirrors

This is a short tutorial on how to draw ray diagrams for plane mirrors. Click on the images to view a larger version.

Initially, we have an object in front of a plane mirror.

## First, we draw an image of the object on the other side of the mirror

Distance A is equal to distance B and the image size is the same size as the object size.

## Second, we draw light rays from the image to the eye

The image is virtual. Broken lines from the image to mirror indicate virtual rays. Virtual image: Light rays do not actually meet at the image position. Because of that, a virtual image cannot be projected on a screen.

Continuous lines from the mirror to eye indicate the reflected rays.

## Third, we join the light rays from the mirror to the object

Lines joining the object to the positions of the reflected rays on the mirror represent the incident rays.

## Properties of the image formed in the plane mirror:

• Same size as object
• Laterally inverted (Left becomes right, right becomes left)
• Upright
• Virtual
• As far behind the mirror as the object is in front