Light

Light INFO on light, sunscreen, sunblock, absorption & UV rays posted by Ben Khabib:

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here are some common terms defined that are used throughout the light chapter:
 * Revision for you by Balkaran Mann:**
 * Refraction:** is used to describe the bending of a light ray as it passes into a different substance
 * Optical density:** how much a substance is able to bend light. When light travels from a substance that is of higher optical density say for example from air to glass the light will slow down and bend towards the normal. However when light travels into a substance of lower optical density lets say from glass to air the light speeds up and bends away from the normal.
 * illusion:** an example of illusion is when you dip a ruler from air into water our brain constructs an image based on where light coming from the lower part of the ruler appears to come from and what we see is that the lower part of the ruler appears to be bent away from the normal.
 * Apparent depth:** Is used to describe how deep a pool for example appears to be. it is noticeable when we go to the swimming pool at the deep end the pool appears to be less deep than it actually is.
 * Total internal reflection:** well it occurs when light travels into a substance of lower optical density and strikes the substance at an angle greater than the critical angle of incidence and this causes the light to reflect as it is trapped within the substance and is unable to escape.
 * Convex lenses:** are lenses that are fatter in the middle and curve outwards.
 * Concave lenses:** These lenses curve inwards and are thinner in the middle.
 * Principal focus:** where parallel rays of light meet after passing through lens.
 * principal axis:** line that goes through the middle of the lens and contains the focus.
 * Real image:** is formed when when the object is at a greater distance than the focal length of the lens, the real image can be projected.
 * Virtual image:** is the opposite of a real image and is when the object is placed at a distance less than the focal length of the lens. This image cannot be projected onto a screen and is produced by concave lenses.
 * How telescopes work:** Well the telescope uses the objective lenses to produce a real, inverted image just inside the focus of the eyepiece lens. The eyepiece lens then produce an enlarged virtual image of the first image.
 * How binoculars work:** Well binoculars use two telescopes and use triangular prisms to redirect light and make sure images are upright.
 * How microscopes work:** light is reflected from a mirror through a condenser to focus light through the specimen you are viewing and then that light passes through the objective lens which produce a real image inside the focal length of the eyepiece lens which then magnify that image into a virtual image that is directed to your eyes.
 * How slide projector works:** Well a slide projector contains a concave mirror which reflects light from a bulb through a condenser which then focus that light through a slide placed outside the focal length of the projection lens. The projection lens produce a magnified real image on to the screen.
 * Spectrum:** refers to the colours of the rainbow.
 * Scattering:** molecules of gas and dust particles in the atmosphere alter the direction of light rays.
 * Rainbow:** can be described as an arc of colored light in the sky caused by refraction of the sun's rays by rain.