Reflection of a Ray of Light

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The diagram shows an incident ray of light approaching the boundary between air and glass.


  • When the ray strikes the boundary between air and glass it bounces off the surface of the glass because it is highly reflective.
  • The diagram demonstrates that the angle of incidence and angle of reflection are the same.
  • The angles of incidence and reflection are both measured between the ray and the normal (the dotted green line).
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Description

Reflection of a Ray of Light

TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
The normal is an imaginary line drawn on a ray-tracing diagram perpendicular to, so at a right angle (90 degrees), to the boundary between two media.
_x000D_ _x000D_ Reflection takes place when incoming light strikes the surface of a medium, some wavelengths are obstructed, and the wavefront bounces off and returns into the medium from which it originated.
Incident light refers to incoming light that is travelling towards an object or medium.

About the diagram

Overview of this page

  • This page provides an introduction to reflection.
  • Related topics including refraction and dispersion are covered on other pages of this series.
  • Introductions to refractive index and the law of refraction (sometimes called Snell’s law) also appear on subsequent pages.

About the diagram

  • You will notice that this diagram looks at reflection but for simplicity ignores refraction and dispersion.
  • It looks at the path of white light rather than at the paths of the different wavelengths that white light contains.
  • The diagram shows an incident ray of white light approaching the boundary between air and glass.
  • When the ray strikes the boundary between the air and the glass it bounces back off the surface of the glass because it is highly reflective.
  • The diagram shows that the angle of incidence and angle of reflection are the same.
  • Both the angle of incidence and the angle of reflection are measured between the ray and the normal (the dotted green line).

Reflection

  • Reflection takes place when incoming light strikes the surface of a medium and the light bounces off and returns into the medium from which it originated.
  •  Reflection is predictable and always obeys three rules (the laws of reflection):
    • The incident ray, the reflected ray and the normal all lie in the same plane.
    • The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes with the normal.
    • The reflected ray and the incident ray always appear on opposite sides of the normal.
  • Reflection takes place when light is neither absorbed by an opaque medium nor transmitted through a transparent medium.

Types of reflection

  • When sunlight strikes window glass, some light is reflected and some is transmitted through the glass into the room beyond.
  • The type of glass made for picture framing is designed to reflect some wavelengths and to transmit others.
  • When light illuminates objects and then goes on to strike a mirror, the reflected image can be seen by an observer.
  • A reflected image contains objects that we recognise and is made up of visible wavelengths of light and their corresponding colours.
  • If a reflecting surface is very smooth, light waves remain in the same order as they bounce off the surface, producing a specular reflection.
  • A diffuse reflection, in which no image is visible, results from light reflecting off a rough surface and light waves scattering in all directions.
  • Reflection is independent of the optical density of the medium through which incident light travels or of the medium it bounces off.

Incident light

  • Incident light refers to incoming light that is travelling towards an object or medium.

White light

  • White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities.
  • The Sun emits white light because sunlight contains equal amounts of all of the wavelengths of the visible spectrum.
  • As light travels through a vacuum or a medium it is described as white light if it contains all the wavelengths of visible light.
  • As light travels through the air it is invisible to our eyes.
  • White light is what an observer sees when all the colours that make up the visible spectrum strike a white or neutral coloured surface.

Angle of incidence

  • 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.

Angle of reflection

  • 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.

The normal

  •  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.
  • If the boundary between the media is curved then the normal is drawn perpendicular to the boundary.

Some key terms

The Sun is the star at the centre of our solar system.

The visible part of the electromagnetic spectrum is called the visible spectrum.

  • The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
  • As light travels through the air it is invisible to our eyes.
  • Human beings don’t see wavelengths of light, but they do see the spectral colours that correspond with each wavelength and colours produced when different wavelengths are combined.
  • The visible spectrum includes all the spectral colours between red and violet and each is produced by a single wavelength.
  • The visible spectrum is often divided into named colours, though any division of this kind is somewhat arbitrary.
  • Traditional colours referred to in English include red, orange, yellow, green, blue, and violet.

Sunlight is light emitted by the Sun and is also called daylight or visible light.

In physics and optics, a medium refers to any material (plural: media) through which light or other electromagnetic waves can travel. It’s essentially a substance that acts as a carrier for these waves.

  • Light is a form of electromagnetic radiation, which travels in the form of waves. These waves consist of oscillating electric and magnetic fields.
  • The properties of the medium, such as its density and composition, influence how light propagates through it.
  • Different mediums can affect the speed, direction, and behaviour of light waves. For instance, light travels slower in water compared to a vacuum.
  • Examples of Mediums:
    • Transparent: Materials like air, glass, and water allow most light to pass through, with minimal absorption or scattering. These are good examples of mediums for light propagation.
    • Translucent: Some materials, like frosted glass or thin paper, partially transmit light. They allow some light to pass through while diffusing or scattering the rest.
    • Opaque: Materials like wood or metal block light completely. They don’t allow any light to travel through them.
  • The permittivity (electrical response) and permeability (magnetic response) of a medium determine how light interacts with it. These properties influence factors like:
    • Refraction: Bending of light as it travels from one medium to another with different densities.
    • Reflection: Bouncing back of light when it encounters a boundary between mediums.
    • Absorption: Light being captured and converted into other forms of energy (like heat) by the medium.
  • In physics and optics, a medium refers to any material through which light or other electromagnetic waves can travel. It’s essentially a substance that acts as a carrier for these waves.
  • Light is a form of electromagnetic radiation, which travels in the form of waves. These waves consist of oscillating electric and magnetic fields.
  • The properties of the medium, such as its density and composition, influence how light propagates through it.
  • Different mediums can affect the speed, direction, and behaviour of light waves. For instance, light travels slower in water compared to a vacuum.
  • Examples of Mediums:
    • Transparent: Materials like air, glass, and water allow most light to pass through, with minimal absorption or scattering. These are good examples of mediums for light propagation.
    • Translucent: Some materials, like frosted glass or thin paper, partially transmit light. They allow some light to pass through while diffusing or scattering the rest.
    • Opaque: Materials like wood or metal block light completely. They don’t allow any light to travel through them.

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.

Visible light is the range of wavelengths of electromagnetic radiation perceived as colour by human observers.

  • Visible light is a form of electromagnetic radiation.
  • Other forms of electromagnetic radiation include radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
  • Visible light is perceived by a human observer as all the spectral colours between red and violet plus all other colours that result from combining wavelengths together in different proportions.
  • A spectral colour is produced by a single wavelength of light.
  • The complete range of colours that can be perceived by a human observer is called the visible spectrum.
  • The range of wavelengths that produce visible light is a very small part of the electromagnetic spectrum.

Wavelength is a measurement from any point on the path of a wave to the same point on its next oscillation. The measurement is made parallel to the centre-line of the wave.

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