Reflection of a Ray of Light
- 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).
Reflection of a Ray of Light
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About the diagram
Have you already checked out An Introduction to Reflection, Refraction and Dispersion?
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 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 refers to incoming light that is travelling towards an object or medium.
- 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.
- 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 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.
- The wavelength of an electromagnetic wave is measured in metres.
- Each type of electromagnetic radiation, such as radio waves, visible light and gamma waves, forms a band of wavelengths on the electromagnetic spectrum.
- The visible part of the electromagnetic spectrum is composed of the range of wavelengths that correspond with all the different colours we see in the world.
- Human beings don’t see wavelengths of visible light, but they do see the spectral colours that correspond with each wavelength and the other colours produced when different wavelengths are combined.
- The wavelength of visible light is measured in nanometres. There are 1,000,000,000 nanometres to a metre.
- 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.
- In optics, a medium is a material through which electromagnetic waves propagate.
- Although electromagnetic radiation is able to propagate through a wide range of media, it is not dependent upon on any medium for propagation and travels at the speed of light through a vacuum.
- The reason an electromagnetic wave does not need a medium to propagate through is because the only thing that is waving/oscillating is the value of the electric and magnetic fields.
- In general terms, empty space (a vacuum) is not considered to be a medium because it does not contain matter.
- It is the permittivity and permeability of a medium that determines how waves travel.
About sections (temp)
The Sun is the star at the centre of our solar system.
- The energy emitted by the Sun is called electromagnetic radiation or solar radiation.
- The solar radiation that the human eye is sensitive to is often called sunlight or visible light.
- The term light is often used to refer to visible light but can also be used to refer to all the different forms of electromagnetic radiation.
- Sunlight is only one form of electromagnetic radiation emitted by the Sun.
- Sunlight is only a very small part of the electromagnetic spectrum.
- Sunlight is the form of electromagnetic radiation that our eyes are sensitive to.
- Other types of electromagnetic radiation that we are sensitive to, but cannot see, are infrared radiation that we feel as heat and ultraviolet radiation that causes sunburn.
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