# Reflection & Total Internal Reflection

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#### Reflection & Total Internal Reflection

###### TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
As light travels from a fast medium such as air to a slow medium such as water it bends toward 'the normal' and slows down. As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from 'the normal' and speeds up.
Refraction refers to the way light changes both direction and speed as it travels from one transparent medium into another.
_x000D_ _x000D_ A medium is any transparent material through which an electromagnetic wave propagates (plural media).
Yes! When light leaves a vacuum or travels from one transparent medium into another, it undergoes refraction causing it to change both direction and speed.

Have you already checked out An Introduction to Reflection, Refraction and Dispersion?

It is the opening page of our Reflection, Refraction and Dispersion Series and contains masses of useful information. This is the table of contents:

The diagram

• In this diagram sunlight or artificial light travelling through water reflects upwards off the body of the fish.
• For clarities sake,  the diagram doesn’t show light travelling towards the fish.
• Check out our diagram dealing with the way parallel incident light rays scatter in different directions as they are reflected off the body of the fish:  Sunlight Reflects off a Fish in Water
• Notice how the light reflected off the fish and towards the surface is incident to the boundary between water and air.
• As the incident light strikes the surface a proportion is refracted as it crosses the boundary into the air and a proportion is reflected off the surface back into the water.
• The diagram demonstrates the paths taken for a ray travelling parallel to the normal and striking the boundary at right angles and for rays at angles of 150, 300,  45to the normal.
• Notice that the amount of light that is reflected increases as the angle increases but that above 48.60 total internal reflection takes place and all the light is reflected.
• Depending on the angle at which the light strikes the surface, different proportions are refracted or reflected.
• The ratio of the reflected intensity to the incident intensity is called the reflectance (R) and the ratio of the transmitted intensity to the incident intensity is called the transmittance (T).  Energy conservation requires that R + T = 1 (if there is no absorption).
• The reflectance of the surface of a material is its effectiveness at reflecting radiant energy.
• The transmittance of the surface of a material is its effectiveness at transmitting radiant energy.

#### Some key terms

The angle of refraction measures the angle to which light bends as it crosses the boundary between different media.

• The angle of refraction is measured between the bent ray and an imaginary line called the normal.
• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
• Snell’s law is a formula used to describe the relationship between the angle of incidence and the angle of refraction when light crosses the boundary between transparent media, such as water and air or water and glass.

In physics and optics, a wave diagram uses a set of drawing conventions and labels to describe the attributes of light waves including wavelength, frequency, amplitude and direction of travel.

The angle of reflection measures the angle at which light rebounds from a surface after being reflected.

• The angle of reflection is measured between a ray of light which has been reflected off a surface and an imaginary line called the normal.
• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
• The angle of reflection can be used to understand how light will behave when it interacts with different types of surfaces and objects.

The angle of incidence refers to the angle at which incoming light strikes a surface and is measured between a ray of incoming light and an imaginary line called the normal.

• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
• The angle at which incident light from the Sun or a light bulb strikes a surface can affect the outcome. For instance, when incident light hits a mirror, the angle of incidence determines the angle of reflection.

As light crosses the boundary between two transparent media, the law of refraction (Snell’s law) states the relationship between the angle of incidence and angle of refraction of the light with reference to the refractive indices of both media as follows:

When electromagnetic radiation (light) of a specific frequency crosses the interface of any given pair of media, the ratio of the sines of the angles of incidence and the sines of the angles of refraction is a constant in every case.

• Snell’s law deals with the fact that for an incident ray approaching the boundary of two media, the sine of the angle of incidence multiplied by the index of refraction of the first medium is equal to the sine of the angle of refraction multiplied by the index of refraction of the second medium.
• Snell’s law deals with the fact that the sine of the angle of incidence to the sine of the angle of refraction is constant when a light ray passes across the boundary from one medium to another.
• Snell’s law can be used to calculate the angle of incidence or refraction associated with the use of lenses, prisms and other everyday materials.
• When using Snell’s law:
• The angles of incidence and refraction are measured between the direction of a ray of light and the normal – where the normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.
• The wavelength of the incident light is accounted for.
• The refractive indices used are selected for the pair of media concerned.
• The speed of light is expressed in metres per second (m/s).

The angle of reflection is the angle between the incident light ray and the reflected light ray, both measured from an imaginary line called the normal.

• According to the law of reflection, the angle of incidence (the angle between the incident ray and the normal) is always equal to the angle of reflection.
• The angle of reflection is measured between the reflected ray of light and an imaginary line perpendicular to the surface, known as the normal.
• In optics, the normal is a straight line drawn on a ray-tracing diagram at a 90º angle (perpendicular) to the boundary where two different media meet.
• Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
• If the boundary between two media is curved, the normal is drawn perpendicular to the tangent to that point on the boundary.
• Reflection can be diffuse (when light reflects off rough surfaces) or specular (in the case of smooth, shiny surfaces), affecting the direction of reflected rays.
###### References

https://en.wikipedia.org/wiki/Reflection_(physics)

• The angle of reflection measures the angle at which reflected light bounces off a surface.
• The angle of reflection is measured between a ray of light which has been reflected off a surface and an imaginary line called the normal.
• See this diagram for an explanation: Reflection of a ray of light
• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
• If the boundary between the media is curved then the normal is drawn perpendicular to the boundary.

Reflection takes place when incoming light strikes the surface of a medium, obstructing some wavelengths which bounce back into the medium from which they originated.

Reflection takes place when light is neither absorbed by an opaque medium nor transmitted through a transparent medium.

If the reflecting surface is very smooth, the reflected light is called specular or regular reflection.

Specular reflection occurs when light waves reflect off a smooth surface such as a mirror. The arrangement of the waves remains the same and an image of objects that the light has already encountered become visible to an observer.

Diffuse reflection takes place when light reflects off a rough surface. In this case, scattering takes place and waves are reflected randomly in all directions and so no image is produced.

The angle of incidence measures the angle at which incoming light strikes a surface.

• When light is travelling towards something it is said to be incident to that surface or object.
• The angle of incidence is measured between a ray of incoming light and an imaginary line called the normal.
• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
• Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
• Incident light may have travelled from the Sun or a man-made source or may have already been reflected off another surface such as a mirror.
• When incident light strikes a surface or object it may undergo absorption, reflection, refraction, transmission or any combination of these optical effects.
###### References
• The angle of incidence measures the angle at which incoming light strikes a surface.
• The angle of incidence is measured between a ray of incoming light and an imaginary line called the normal.
• See this diagram for an explanation: Reflection of a ray of light
• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
• If the boundary between the media is curved, then the normal is drawn at a tangent to the boundary.

Refraction refers to the way that electromagnetic radiation (light) changes speed and direction as it travels across the interface between one transparent medium and another.

• As light travels from a fast medium such as air to a slow medium such as water it bends toward the normal and slows down.
• As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from the normal and speeds up.
• In a diagram illustrating optical phenomena like refraction or reflection, the normal is a line drawn at right angles to the boundary between two media.
• A fast (optically rare) medium is one that obstructs light less than a slow medium.
• A slow (optically dense) medium is one that obstructs light more than a fast medium.
• The speed at which light travels through a given medium is expressed by its index of refraction.
• If we want to know in which direction light will bend at the boundary between transparent media we need to know:
• Which is the faster, less optically dense (rare) medium with a smaller refractive index?
• Which is the slower, more optically dense medium with the higher refractive index?
• The amount that refraction causes light to change direction, and its path to bend, is dealt with by Snell’s law.
• Snell’s law considers the relationship between the angle of incidence, the angle of refraction and the refractive indices (plural of index) of the media on both sides of the boundary. If three of the four variables are known, then Snell’s law can calculate the fourth.

If one line is normal to another, then it is at right angles. So in geometry, the normal is a line drawn perpendicular to and intersecting another line.

In optics, the normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.

• Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
• Light travels in a straight line through a vacuum or a transparent medium such as air, glass, or still water.
• If light encounters a force, an obstacle or interacts with an object, a variety of optical phenomena may take place including absorption, dispersion, diffraction, polarization, reflection, refraction, scattering or transmission.
• Optics treats light as a collection of rays that travel in straight lines and calculates the way in which they change direction (deviate) when encountering different optical phenomena.
• When the normal is drawn on a ray diagram, it provides a reference against which the amount of deviation of the ray can be shown.
• The normal is always drawn at right angles to a ray of incident light at the point where it arrives at the boundary with a transparent medium.
• Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.

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