Content code
s1143
Slug (identifier)
deviation-of-light-waves
Grades
Secondary III
Topic
Science and Technology
Tags
refraction of light
rainbow
light deviation
dispersion
light reflection
specular reflection
diffuse reflection
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To visualize the propagation of light, the light rays are represented by straight and thin arrows. The arrows are oriented so their starting point is the light source and the arrow indicates the direction the light is travelling in.

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The arrows indicate the direction of the light rays emitted by the projector bulb (light source).

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Light is represented by thin arrows coming out of the projector.
Title
Representation of light rays by arrows
Title (level 2)
Reflection of Light
Title slug (identifier)
reflection
Contenu
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Corps

Light reflection is the phenomenon where light rays bounce off a surface.

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There are two types of light reflection depending on the direction of the reflected rays: specular reflection and diffuse reflection.

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When light rays encounter a perfectly flat or polished surface, they are reflected in a parallel manner. It is called a specular reflection.

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On a smooth surface, light rays are reflected in a parallel manner.
Title
Diagram of specular reflection
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When light rays encounter an uneven or rough surface, they are reflected in all directions. It is called diffuse reflection.

Image
On an uneven surface, light is reflected in all directions.
Title
Diagram of diffuse reflection
Title (level 3)
Specular Reflection
Title slug (identifier)
specular
Corps

When light strikes a perfectly smooth surface, all light rays are reflected symmetrically. Therefore, all the reflected rays are parallel to each other and the image formed is identical to the object.

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Both situations illustrate specular reflection. We observe the formation of two identical images of a dog. One of the images is formed in a puddle and the other is formed in the side mirror of a car.

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Image
Specular reflection of a dog in a puddle
Title
Specular reflection of a dog and the sky in a puddle
Description
Bachkova Natalia, Shutterstock.com
Second column
Image
Specular reflection of a dog in a car side mirror
Title
Specular reflection of a dog and the landscape in a car side mirror
Description
Photo TrippingAmerica, Shutterstock.com
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An observer can see the cat's reflection on the surface of the mirror, because the light rays are reflected parallel to and towards the observer’s eye.

Image
The mirror is a perfectly smooth surface; therefore, the light rays are reflected in parallel towards the observer’s eye.
Title
Observing the image of a cat
Description
Adapté de anmbph, Shutterstock.com
Corps

Determine the Angle of Reflection on a Plane Mirror

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Corps
  • The incident ray is the one directed towards the reflective surface (mirror).

  • The point of incidence is where the incident ray hits the mirror.

  • The normal is a line perpendicular to the mirror drawn at the point of incidence of the light ray.

  • The reflected ray is the ray leaving the reflective surface.

  • The angle of incidence |(\theta_\text{i})| is the measure of the angle between the incident ray and the normal.

  • The angle of reflection |(\theta_\text{r})| is the measure of the angle between the reflected ray and the normal.

Image
Diagram of the reflection of light in a plane mirror.
Title
The reflection of light in a plane mirror
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During reflection, the light ray is reflected at the same angle as the incident ray relative to the normal.

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The angle of incidence and the angle of reflection are of equal values.
Title
Angle of incidence and angle of reflection
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Corps

|\theta_{i}=\theta_{r}|

where

|\theta_{i}| is the measure of the angle of incidence in degrees |(^{\circ})|
|\theta_{r}| is the measure of the angle of reflection in degrees |(^{\circ})|

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Determine the angle of reflection when an incident ray hits a mirror at an angle of |67^{\circ}| relative to the mirror.

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Image
A light ray reaches a plane mirror at an angle of 67° relative to the mirror.
Title
Incident ray
Solution
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Here, the angle between the incident ray and the mirror is given. Use the value to determine |\theta_{i},| the measure of the angle between the normal and the incident ray.

|\theta_{r}=?|

The normal forms an angle of |90^{\circ}| with the mirror.

|\begin{align}\theta_{i}&=90^{\circ}-67^{\circ}=23^{\circ}\\ \theta_{i}&=\theta_{r}\\ \theta_{r}&=23^{\circ}\end{align}|

So, the measure of the angle of reflection is |23^{\circ}.|

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Image
The reflected ray is at an angle of 23° relative to the normal.
Title
The calculation of the angle of reflection
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Determine the angle of reflection in the graph shown on the right.

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A light ray hits a plane mirror at an unknown angle.
Title
Incident ray
Solution
Corps

|\theta_{r}=?|

To determine the angle of reflection graphically, use a protractor and a square.

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Using the square, draw the normal perpendicular to the mirror at the point of incidence.

The normal must form an angle of |90^{\circ}| with the mirror.

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The normal to the point of incidence has an angle of 90° relative to the mirror.
Title
Drawing the normal
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Using the protractor, measure |\theta_{i}| (the angle between the normal and the incident ray).

It comes to |45^{\circ}.|

Therefore, |\theta_{i}=45^{\circ}.|

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The incident ray has an angle of 45° relative to the normal.
Title
Measure of the angle of incidence
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Corps

Because |\theta_\text{i}=\theta_{r},|

|\theta_{r}=45^{\circ}|

The measure of the angle of reflection is |45^{\circ}.|

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Image
The reflected ray has an angle of 45° from the normal.
Title
The calculation of the angle of reflection
Content
Text

The following concepts are covered in Secondary 5 physics.

Links
Title (level 3)
Diffuse reflection
Title slug (identifier)
diffuse
Corps

Diffuse reflection occurs on uneven surfaces.

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Fabrics, grass, and an orange peel are examples of uneven surfaces on which light is diffusely reflected.

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A pile of fabric of various colours.
Title
Pile of fabric
Description
Riderfoot, Shutterstock.com
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Image
Grass
Title
Grass
Description
Jon Rehg, Shutterstock.com
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Image
Orange peel
Title
Orange peel
Description
domnitsky, Shutterstock.com
Content
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A cat's fur is an uneven surface. Light rays that hit the fur parallel to each other are reflected in all directions. This phenomenon is represented by the white and orange arrows.

Image
A cat’s fur is not a perfectly smooth surface; therefore, light is reflected in all directions.
Title
Illustration of the diffuse reflection of light on a cat’s fur
Description
Adapté de andia, Shutterstock.com
Corps

Diffuse reflection does not produce a reflection like in a mirror, but it allows us to observe the world around us. Visible light is actually reflected on objects, and then in all directions including our eyes, the organs of sight.

The way light is reflected by objects tells us about their colour, shape, etc. Without the reflection of light, humans would live in complete darkness.

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When the orange light is reflected and the other colours are absorbed, the eye perceives the orange colour only.

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An orange surface absorbs all colours and reflects orange light.
Title
Diffuse reflection of orange light
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The orange light is reflected off the dog towards the cat’s eyes, the other colours are absorbed.
Title
The observation of a dog by a cat
Description
Adapté de Chendongshan, Shutterstock.com
Title (level 2)
Refraction of Light
Title slug (identifier)
refraction
Contenu
Content
Corps

Refraction is the deflection (bending) of a light ray as it passes from one transparent medium to another.

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Media with the ability to deflect light rays are called refractive.

When light travels through a transparent medium (e.g., air), its speed is constant. However, if it passes through another transparent medium (for example, water), its speed of propagation changes. The change in speed causes the ray to deviate from its original path.

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  1. A light ray travels through the air at a constant speed. The light ray is not deflected.

  2. A light ray travels through the air and then through the water. As it enters water, the speed of light changes. The light ray is deflected, and continues to travel.

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Image
Comparison of a light ray transmitted through the air (not deflected) with a light ray passing from air to water (deflected).
Title
Propagation of light through the air and water
Corps

Refraction changes our perception of objects when viewed through a transparent medium.

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When we dip a pencil in a glass of water, a distorted and shifted image of the pencil can be observed.

Image
The deflection of light in water produces a distorted image of a pencil.
Title
Perception of a deformed pencil in water
Description
Kuki Ladron Guevara, Shutterstock.com
Corps

By using a curved transparent medium such as a lens, light can be deflected.

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In the lab, a light source emits three parallel light rays towards a converging lens. The following facts can be observed:

  • Light rays pass through the converging lens.

  • As they exit the lens, the light rays are deflected and come closer together.

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The parallel rays pass through a biconvex lens and are then deflected in a convergent manner.
Title
Deflection of light through a converging lens
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In the lab, a light source emits three parallel light rays towards a diverging lens. The following facts can be observed:

  • The light rays pass through the diverging lens.

  • As they exit the lens, the light rays are deflected and move away from each other.

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Image
The parallel rays pass through a biconcave lens and are then deflected in a divergent manner.
Title
Deflection of light through a diverging lens
Content
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Light dispersion is the optical phenomenon that explains why white light is separated into its constituent colours when passing through a transparent medium.

Corps

In a rainbow, the water droplets suspended in the air act like prisms, separating the colours.

During dispersion, the light is separated into seven monochromatic rays (formed by a single ray), namely red, orange, yellow, green, blue, indigo, and violet.

Image
A rainbow is an example of light dispersion in water droplets.
Title
The rainbow
Description
S.Borisov, Shutterstock.com
Content
Text

The following concepts are covered in Secondary 5 physics.

Links
Title (level 2)
Exercise
Title slug (identifier)
exercise
Contenu
Contenu
Title
Deviation of Light Waves
Title slug (identifier)
deviation-of-light-waves
Title (level 2)
See also
Title slug (identifier)
see-also
Contenu
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