Light

• Light usually travels in straight lines. It changes direction if it hits a shiny surface or if it travels from one material to another.
• The change of direction of light on a shiny surface is reflection.
• Modern mirrors give a very clear image.
• When a ray of light reflects off a mirror, the ray bounces off.
• Angle of incidence = Angle of reflection
• The normal is a line drawn perpendicular at 90 degrees to the surface, at the point where the light ray strikes it.
• When light rays are reflected in a mirror, some of them enter the observers eye.
• A mirror image is inverted.
• The image of an object in a mirror is not a real image, it is a virtual image.
• When an object is reflected onto a plane mirror, its image is the same size as the object, the same distance behind the mirror as the object is in front of it, it is inverted, and virtual.
• Bending of light rays as they travel from one material through another is called refraction.
• A change in material causes the bending of light.
• A ray bends towards the normal when entering glass, and away from the normal when leaving glass.
• A refracted ray travels on at the angle of refraction.
• A ray of light may strike a surface so that the angle of incidence is 0, this means the light does not bend and passes straight through in the same direction.
• Light travels ery fast.
• Refractive index = sin i (angle of incidence)/sin r (angle of refraction)
• If the angle of incidence is small, most of the light emerges from the glass and the refracted rays ben away from the normal.
• If the angle of incidence is increased, more light is reflected inside the glass. The refracted ray bends even further from the normal.
• If the angle of incidence is greater than a particular value, known as the critical angle, the light is entirely reflected inside the glass. (Total internal reflection)
• Total Internal Reflection: Total - all the light is reflected, Internal - happens inside the glass, Reflection - the ray is entirely reflected
• For total internal reflection to occur, the angle of incidence must be greater than the critical angle.
• Telephone messages and other electrical signals such as internet computer messages are passed along fine glass fibers (optical fibers) in the form of flashing laser lights.
• Inside an optical fiber, light travels along by total internal reflection because each time it strikes inside of the fiber, its angle of incidence is great than the critical angle.
• Optical fibers are also used in medicine.
• An endoscope is a device that can be used by doctors to see inside a patients body.
• In an endoscope, one bundle of optical fibers carries light down the body, while the other carries an image back up to the user.
• Converging lenses are fatter in the middle than at the edges.
• Diverging lenses are thinner in the middle than at the edges.
• On one side of a converging lens, the rays are parallel to the axis of the lens. After they pass through the lens, the converge on a single point, the principal focus.
• Converging lens is a lens that makes parallel lines converge.
• A magnifying glass is an example of a converging lens.
• A converging lens can be used in reverse to produce a beam of parallel lights.
• Lenses work by refracting light, when a ray strikes the surface of the lens, it is refracted towards the normal. When it leaves the glass lens, it bends away from the normal.
• An image formed by a converging lens is inverted (upside down), reduced (smaller), nearer to the lens than the object, and real.