Science 8 – Light and Optics

Mr. Parsons

Unit Vocabulary These terms should be familiar to you by the end of this unit. You may want to add additional terms as they come up. No need to memorize definitions but you should be able to use them in discussion.

Incandescence Translucent Refracted RayFluorescent Transparent Laws of ReflectionPhosphorescence Opaque Diffuse ReflectionChemiluminescence Concave MirrorBioluminescence Convex LensLuminous Visible LightNon-luminous Electromagnetic SpectrumReflection Incident RayRefraction Reflected Ray

Sources of Light• Our sun is the primary source of natural light on earth.

• However, there are a number of unique sources of light that can be found. The following are just few.

Phosphorescence- “Glow in the Dark’ objects. Phosphorous in the material is able to store light when it is

present and release it in the absence of light. (Ex. Glow in the Dark stickers.)Bioluminescence - Occurs when living organisms produce their own light from within their bodies. Usually found in organisms who live in the dark. Used to attract prey or scare off predatorsChemiluminescence- Light produced as a result of chemical reactions. When some chemicals are mixed light is

given off as a product of the reaction.*See pages 268-271 in your text.

Sources of Light: Incandescence vs. Fluorescence

The most common sources of artificial are Incandescent lighting and Fluorescent lighting. (See figure to right)

*However, important to note the LED lightning is increasing at an alarming rate. (More later)

Luminous vs. Non-luminous

A luminous object is one that produces light. Ex. Light bulb, candle, match, etc.

A non-luminous object is on that does not produce light but instead reflects light

How light behaves when in comes in contact with matter

• Non luminous objects can be classified as being; transparent, translucent or opaque

How light behaves: Reflection vs. Refraction• Opaque objects reflect light energy. Mirrors are examples of objects that reflect

light. Flat (plane) mirrors follow the laws of reflection.

• Curved mirrors reflect light differently (*more later)• Transparent and Translucent objects refract light energy. Light slows down and

‘bends’ as it passes through transparent and translucent objects.

Curved Mirrors vs. Lenses• Concave mirrors cause reflected light to converge to a focal point

which then causes the image to become inverted (upside down). *Try looking into a shiny, clean spoon.• Convex mirrors cause reflect light to diverge away from mirror

increasing what can be seen in the mirror. * Now turn the spoon around and look at the back.

Curved Mirrors vs. LensesConcave lenses cause refracted light to diverge and can create an image that is enlarged but lacks some detail.

Convex lenses cause refracted light to converge to a focal point and create an image that is inverted (upside down).

*It is important to note that while light behaves similarly in concave mirrors and convex lens one very big difference is that mirrors reflect light while lenses refract light.

Electromagnetic Spectrum

• Electromagnetic Radiation is radiant energy released from electromagnetic processes.

• Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays and gamma-rays are all forms of electromagnetic radiation.

• Fortunately for us, only visible light is able to be seen because our eyes are only designed to receive visible light.

Visible Light• Sir Isaac Newton discovered that white light was made up of the 7

colours of the visible spectrum. ROYGBIV• The visible spectrum is responsible for the colours that we see. For

example, a red apple appears red because it reflects red light energy and absorbs all other light energies.• White objects reflect all light energies while black objects absorb all

light energies. Which would you rather wear on a warm, sunny day?

Primary and Secondary Light Colours

Red, Green and Blue are the primary colours of light. When all 3 are combined these will make white light.

Cyan, Magenta and Yellow are the secondary colours of light. Any 2 of these will make white light when combined.- Cyan is made when green and blue light are combined. Red is complementary- Magenta is made when red and blue light are combined. Green is complementary- Yellow is made when red and green light are combined. Blue is complementary

*It is important to note that pigments colours are not the same as light coloursas shown in the figure

The EyeSclera – The white of the eye. Very thick tissue.Iris – The coloured part of the eye. Expands and contracts to control the size of the pupil and amount of light that enters the eye. Pupil – Opening in the iris that allows light into the inner eye and lens.Cornea – Specialized, convex, transparent area of the sclera at the front of the eye. Allows light into the eye.Lens – double convex structure that focuses light onto the retinaRetina – Specialized layer of tissue at the back of the eye. Made up of rod cells (black and white)and cone cells (colour) that act as receptors of light energyOptic Nerve –Carries the electrical message created on the retina to the brain to be processed.

What’s up with LEDs?• Light emitting diodes, commonly called LEDs, are

real unsung heroes in the electronics world. They do dozens of different jobs and are found in all kinds of devices. • Unlike ordinary incandescent bulbs, they don't

have a filament that will burn out, and they don't get especially hot. They are illuminated solely by the movement of electrons in a semiconductor material.• The lifespan of an LED surpasses the short life of

an incandescent bulb by thousands of hours. Tiny LEDs are already replacing the tubes that light up LCD HDTVs to make dramatically thinner televisions.

In case you were wondering…