CH 14: Light

• Light travels in straight lines.
• The speed of light in vacuum is 3 times 10^8 meters per second.
• Light moves slower in optically denser medium like air, glass and water.
• Objects that produce light are luminous objects such as the sun, fire and light bulb.
• An object is seen to be blue because it reflects blue light and absorbs other colored lights.
• An object is seen to be white because it reflects all colored light and an object is seen to be black because it absorbs all color lights.
• When the ray of light hits the surface of non-luminous object it will either be absorbed or reflected by the object.
• The normal is an imaginary line that is perpendicular to the surface.
• The characteristics of a real image are the opposite of those of a virtual image.
• If the distance from the object to the lens is equal to the focal length, a virtual image is formed, which is inverted and magnified.
• When the distance from the object to the lens is greater than 2f, a real image is formed, which is inverted and same size as the object.
• The formula for magnification m is the ratio of image height h i to object height h o, represented as m = h i/h o.
• When the object is at infinity, a real image is formed, which is inverted and diminished.
• The application of a virtual image is a spotlight projecting a bearer beam.
• The ray diagram shows that when the object is between the focal point and the lens, a real image is formed, which is virtual, upright, and magnified.
• The application of a real image is the optical lens of a telescope.
• The application of a real image is a magnifying glass.
• The application of a real image is a photocopier.
• The first law of reflection states that the incident ray, reflected ray and the normal all lie in the same plane.
• Principle reversibility states that an array of light will take the same path if its direction of travel is reversed.
• Apparent depth is greater than actual depth in internal reflection.
• The sine of incident angle i to the sine of refracted angle r when the light travels from vacuum to a medium is n equals c over v equals sine i over sine r.
• When light travels from a denser medium to a less dense medium, the refracted light will bend away from normal.
• Due to the difference in speed, light bends towards normal when it travels into an optically denser medium and bends away from normal when it travels into an optically less dense medium.
• If a medium has a higher refractive index, it is optically denser and light travels faster in a medium which is optically less dense.
• Refractive index has no units.
• Binoculars use glass prisms with different critical angles to allow light to be internally reflected, bend lights and help binoculars compact.
• In a strong inner glass of water, light bends away from normal due to refraction.
• Prism uses total internal reflection to bend light and form an image.
• The second law of reflection states that the angle of incident i is equal to the angle of reflection r, so i equals to r.
• Laws of reflection are always obeyed, for example, if the surface is smooth, all light rays will reflect according to law of reflection.
• If the surface is convex, a ray shining at the center point will return to the original path.
• If the surface is concave, a ray shining through the center will return at the same path.
• Reflection on mirror is a virtual image that is same size as the object, cannot be projected on a screen, upright and at the same distance from the mirror as the object.
• When a ray of light travels from a transparent medium to another transparent medium at certain angle, part of the light is reflected at the boundary while the rest bends into the other medium, this is known as refraction of light.
• When a ray of light travels into the optical center of a converging lens, it continues to travel in a straight line.
• The distance between the focal point to the optical center is the focal length of the lens.
• Thin lenses are of two types: converging lens and diverging lens.
• High refractive index require low critical angle, hence light is easily internally reflected at the boundary of the two materials.
• Advantages of optical fibers include low power loss, higher bandwidth, no electromagnetic interference, smaller size, lightweight, and less space compared to metal wires.