Introduction to Optics

1. The Great Debate 2. What is light? 3. Properties of light 4. The wave-like model 5. Theories of colour

 A historical debate:

 Optics: is the study of the behaviour and properties of light

 Light: is a form of energy that travels in waves  Wave: is a disturbance that transfers energy from one point to another without transferring matter  We can use the properties of water waves to help us understand light waves (demonstration)  We use waves on the surface of water to explain properties of light that we can see  This is called a “model” a representation of an object, event or a process based on our observations of its characteristics and properties

 Crest: Highest point in a wave  Trough: Lowest point in a wave  Rest Position: Level of water when there is no waves  Wavelength: distance from one place in a wave to the next similar place on the wave. The symbol for wavelength is λ (lambda) and is measured in meters.  Amplitude: wave height from the rest position of the wave to the crest OR trough  Frequency: rate of repetition of a wave. The frequency is measured in hertz (Hz) which is cycles per second.

Label the diagram:

 Relationship between Frequency and Wavelength ν= f λ ν= the speed of light f= frequency f = 1/ λ λ = wavelength λ = 1/f  There is an inverse relationship between frequency and wavelength. When frequency increases, wavelength decreases, when wavelength increases, frequency decreases. How would energy relate?

 Light is a form of energy. Light travels in packets of energy called photons.  A photon is the smallest quantity of energy which can be transported.  Photons travel with wave-like properties Properties of Light  Light travels in straight lines (rectilinear propagation)  Light does not need a medium to travel, it travels in a vacuum - empty space with no matter  In vacuum or air, speed of light is constant (c = 3.0 x 10 8 m/s)

 Speed = distance/time or  If c = 3.0 x 10 8 m/s, then what is it in km/s? ( km/s)  EXAMPLE #1 Calculate the time for light to travel from Toronto to Vancouver (d = 3400 km) c = 3.0 x 10 8 m/s  EXAMPLE #2 How long will it take for light to travel from the Moon to the Earth? (d = km) c = 3.0 x 10 8 m/s  Example #3 How long would it take a jet plane to travel this distance with the speed of 900 km/h, in days?

 The light that we see is called visible light, and is only a fraction of the energy that surrounds us  Electromagnetic radiation: wave pattern made of electrical and magnetic fields that can travel through empty space. The range is called electromagnetic spectrum

 It is called visible light because that is the only part of the spectrum which our eyes have evolved to detect.  The wavelengths of visible light range from (micrometer – of a meter)  Only objects within that size range will absorb and reflect light of that wavelength.  When light passes through a glass prism the light separates into the colours of the rainbow: Red Orange Yellow Green Blue Violet  This is called the visible spectrum

 Colours of the visible spectrum have different wavelengths:  Which colour has the longest λ, which has the shortest? ColourFrequency (Hz)Wavelength (nm) Red4.3 X Orange5.0 X Yellow5.2 X Green5.7 X Blue6.4 X Violet7.5 X

 Additive colour theory: white light is composed of different colours of light.  It is possible to produce white light by combining only three colours.  RED + GREEN + BLUE = primary colours = white light  2 primary colours = secondary colour (cyan, yellow, magenta)

 The subtractive colour theory of light: coloured matter selective absorbs different colours or wavelengths of light. The colours that are absorbed are subtracted from the reflected light that is seen by the eye.  A black object absorbs all colours, white objects reflect all colours.  Primary subtractive colours : cyan, magenta and yellow. Secondary subtractive colours are red, green, blue  a blue object reflects blue and absorbs all other colours  This theory applies to pigments and dyes

 An electron orbiting the nucleus of an atom receives sufficient energy to jump to a higher orbital shell. When it loses energy and falls back to the lower shell the energy it releases escapes in the form of a photon, or particle of light (and you see LIGHT)

 Incandescence: is the emission of light from a hot body due to its temperature. Ex. Light bulb (filament is heated to high temperature and glows)  Chemiluminescence: emission of light and heat as the result of a chemical reaction without a rise in temperature (called cool light). Ex. Glow sticks  Bioluminescence: ability for plant and animals to produce light. Occurs in marine animals.