Light travels in straight lines: Laser

Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

1)Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang.

We see things because they reflect light into our eyes: Homework

Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objectsReflectors

Shadows Shadows are places where light is “blocked”: Rays of light

Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror

The Law of Reflection The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!

Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

Red Orange Yellow Green Blue Indigo Violet

White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow

The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light White light

If we look at a coloured object in coloured light we see something different. For example, consider a football kit: White light Shorts look blue Shirt looks red

In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue

Be TRANSMITTED laser aimed at water or glass Be REFLECTED specular reflection of light by a mirror diffuse reflection of the light in this room off all the other students reflection is re-radiation of light by the electrons in the reflecting material Be ABSORBED Cyan light shining on a red apple is absorbed by electrons in the apple Something new!! A light wave shining on molecules in the air or plastic or other “transparent” materials can be: SCATTERED Light ray moves over to the side in all directions rather than forward, backward or being absorbed. Intensity of the scattered light can depend on wavelength

Speed of light in empty space is c = 3 x 10 8 meters/sec Ray Waveform Amplitude (maximum height) The intensity of the light is proportional to the amplitude squared. Large amplitude means bright light. Low amplitude means dim light Wavelength

Light consists of electric (and magnetic) fields moving through space at the speed of light

Human eyes are only able to process information from the visible part of the spectrum Toward longer wavelengths, the spectrum includes infrared light, microwaves, and radio Toward shorter wavelengths, the spectrum includes ultraviolet light, X-rays, and gamma rays All of these are forms of electromagnetic radiation

What we see as white light is actually made up of a continuum of components Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV) There is actually a continuous transition of color, each with its own wavelength and frequency

Red light has an approximate wavelength of 7.0 x m and a frequency of 4.3 x Hz Violet light has an approximate wavelength of 4.0 x m and a frequency of 7.5 x Hz

Rayleigh Mie Geometric

Blue sky Red Sunset Blue water (from underwater)

The shorter the wavelength, the more light is scattered blue is scattered more than red. this is why the sky is blue and sunsets are red. Think of white light from sun as a mixture of R, G and B Blue is scattered the most so sky looks blue when we look away from the sun

Earth Atmosphere Rays from Sun (not scattered) White or yellow

Larger particles scatter red as well as blue and hence look white. Dust or smoke Clouds; Milk; There are many other types of scattering…

Explains scattering around larger droplets such as Corona around the sun or moon, and similar phenomena.