Light and Optics January 5-21 Miss Sunderland HPS
Light Sources There are two types of light • Natural- still happen if people didn’t exist • Constructed- Man made Is the moon a light source?
Rectilinear Propagation • Light Spreads out in all directions from the source • The light moves in straight lines and reflects off walls, doors, floors, desks etc. Everything you can see reflects light to some level
Shadows • When an object blocks light it creates a shadow. • Shadows have two parts, the umbra and the penumbra. • The dark part of the shadow is called the umbra, it blocks the most light • The lighter fuzzier part of the shadow is called the penumbra, it is caused by some light not being blocked
Shadows • When the sun is LOW in the sky there are long shadows. • Early morning and late evening- why does this happen?
Opaque, Transparent, Translucent Matter can be classified in three different ways, according to how light moved through it. • Opaque- no light can pass through • Transparent- all light can pass through • Translucent- some light can pass through
Refraction • When light passes from one medium (or material) to another it can bend the beam. This is called refraction. • When you view an object in another medium (for example water) it appears to be where it is not. This is an optical illusion. • Remember The Hatchet
Refraction 2 • Sometimes objects appear “broken” when viewed passing through two different mediums.
Lenses and Mirrors • Both create an illusion • Both can be convex or concave • Both change how an image appears • The focal point is where the rays meet after being reflected or passing through the lens.
Convex Lenses Convex – the lens is thicker in the middle - the rays of light come together - the object appears smaller - the object sometimes flips upside down - can be single or compound - called converging lens
Concave Lens • Concave – the lens is thinner in the middle - the rays of light spread out - the object appears larger - can be single or compound - called diverging lens - image is often blurry and out of focus
Electromagnetic Radiation The sun gives off more then just visible light. It gives off many different waves. These all travel in straight lines. This is known as Rectilinear Propagation. These waves travel at different wavelengths.
Rainbow • We can use a prism to split white light into a spectrum of all visible colours. This is also known as a RAINBOW R- red* red has the highest wavelength O- orange Y- yellow G- green B- blue I- indigo V- violet * purple has the lowest wavelenth
Light Spectrum • What appears to be “white” light is actually a combination of ALL visible colours • What appears to be “black” is actually the lack of all colours
Why something is that colour • An object appears a certain colour because it reflects that colour in the visible spectrum of light. This is what your eye picks up. • The object absorbs all other colours.
Colour Subtraction Normally we see objects with all the visible spectrum available. What happens when we view objects in a coloured light? (ex: green light)
Subtracting Light • Usually colours on the opposite side of the colour wheel cancel each other out. They absorb that colour. • Why?
Photography • Modeling • Makeup • Theatre
Why Opposites? The colour absorbs the most and reflects the least (remember no reflection = black) Why doesn’t this always work? - Printers and dyes use many colours and hues combined to form colours.
Questions about the eye. Using what you know about lenses, refraction, reflection and absorption make a hypothesis about how the three parts of the eye work. • Lens & Cornea • Aqueous & Vitreous humor • Retina
The eye has many different parts, this is how it all works • Light from a source hits an object • The object absorbs most light and reflects the rest • The light hits the cornea and is slightly refracted • The light hits the aqueous humor and is slightly refracted • The light passes through the lens and is flipped upside down • The light passes through the vitreous humor and is refracted
7. Light hits specific cones and rods 8. Rods (more numerous & sensitive about 120 million) are excited and send signal through the optic nerve to the brain to tell where and the intensity the light is coming from 9. Cones (less numerous, 7-9 million, 3 types red, green & blue) are excited by different colours and based one which ones are excited, send signal through the optic nerve to the brain to tell the colour of light 10. The brain collects all the signals and interprets them (by flipping them right side up and determining placement, colour and distance).
Other Parts of the Eye The Eyelashes- Keep dust and other particles out of the eye The Tearducts- help moisturize the eye The Iris- the muscle that allows different amounts of light into the eye The Retina- the covering of cones and rods on the back of the eyeball
Black Light How does Black light Make things Appear?
Important reminder • The image you see when looking through a lens or in a mirror is NOT the real thing. It is called a virtual image.
Optical Illusions Sun Dogs Review Mirror