Light Chapter 19

EM Spectrum Electromagnetic Spectrum (EM) - includes radio waves, microwaves, infrared waves, ultraviolet rays, x-rays, gamma rays, and visible light.

Electromagnetic Waves Are transverse waves that are produced by the motion of electrically charged particles. These waves are often called electromagnetic radiation because they radiate from particles.

EM Waves Do not need a medium to transfer energy. They can travel through a vacuum at a speed of 300 000 km/s.

Describing EM Radiation All EM waves travel at the same speed in a vacuum, but their frequency and wavelengths can vary.

EM Spectrum Low Frequency, Long-wave length radio waves to high frequency, short wavelength gamma rays. Page 529.

EM Waves Radio Waves Infrared Radiation Visible Radiation- only part of spectrum we can see. Ultraviolet Radiation – X-Rays and Gamma Rays

Light Facts A. Light travels in a straight line at a speed of 300,000 km per second. B. Light needs no medium in order to travel. It can move through a vacuum. C. When light strikes matter three things can happen – it can be absorbed, reflected, or transmitted.

Absorbed Light that is absorbed is taken in by the matter it strikes. Black objects absorb all light-best color for absorption.

Reflected Light that is reflected bounces off the substance it strikes. Example: Mirrors

Transmitted Light Light that is transmitted passes through the matter it strikes. Examples: Window glass, water, and air. Translucent – objects that you can see light through but not any details examples are waxed paper and frosted glass. Opaque substances cannot be seen through at all Examples: wood and metal.

Reflection Reflected light is bounced light. How to predict how reflected light will behave. A single beam of light is called a ray. Incident ray is the ray that hits a mirror. Reflected ray is the ray that bounces off the mirror.

Refraction Light travels in a straight line. Light can bend and change direction ie. Reflection, refraction Refraction is when light passes at an angle from one medium into another medium so it changes direction or bends. Example: you may have experienced refraction when reaching into a fish tank to pick up an item.

Light travels at different speeds through different mediums. The speed light travels depends upon the density of the medium.

Light that moves straight on from one medium to another does not bend Light that moves straight on from one medium to another does not bend. It is not refracted.

What is the spectrum? Prism is an object that breaks up light into the visible spectrum. Colors of the visible spectrum ROY G BIV (order never changes) red, orange, yellow, green, blue, indigo, violet Variety of colors depends upon the frequency of light energy. Every color has a different frequency. Red has the lowest frequency. And violet has the highest frequency.

What gives an object its color? The color we see depends upon whether the object is opaque or transparent. The color also depends upon how much of the light is reflected, absorbed, or transmitted.

What color do you see? Concave Mirror Focuses Colors                                                              

Opaque Objects Opaque Objects – The color of the object is the color reflected. Red objects reflect red light. White objects reflect all the colors that make up white light. Black objects absorb all colors that strike it.

Transparent Objects Transparent Objects – The color of a transparent object is the color that passes through the object. (all other colors absorbed). Transparent objects transmit only some colors and others are absorbed or blocked – these substances are called filters.

What is a lens? Lens is a transparent substance that bends or refracts light in a definite way. Can be glass or plastic. Found in every optical device ie. Binoculars, telescopes… Have one or two curved surfaces.

Two main types of lenses convex lens is thicker at the center than at the edge. Magnifies to make things look bigger. A convex lens focuses light rays. The point where the light rays meet or converge is called the focal point. Used in projectors and cameras.

Concave lens This lens is thinner at the center than at the edge. Makes things look smaller Spreads out light rays. Often used with convex lenses to give a sharper image.

How do we see? Eye has several transparent parts. Each part refracts light that enters the eye. In a normal eye, light rays converge exactly upon the retina. The retina is the back part of the eye, made of two kinds of nerves. Rods - sensitive to brightness but not color. Cones –sensitive to color.

How do eyeglasses help? Normal eyes see clearly. The light rays enter the eye and converge upon the retina. Some eyes however, the length of the eyeball is not right. It is either too long or too short which causes the image to be out of focus.

Two types of blurred vision: near sightedness – slightly longer eye. Light rays meet in front of retina. Corrected by concave lenses. Farsightedness – slightly shorter eye. Light rays meet beyond the retina. Corrected with convex lens. Draw Concave lens Draw Convex Lens

Convex Lens is Inverse of Concave Lens                                              

Image Formation with Lenses If object is far from the lens (beyond) the focal point, a real inverted image is formed