LightLight

Chapter 19Chapter 19

EM SpectrumEM Spectrum

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

Electromagnetic WavesElectromagnetic 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 WavesEM 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 RadiationDescribing EM Radiation

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

EM SpectrumEM Spectrum

• Low Frequency, Long-wave length radio waves to high frequency, short wavelength gamma rays.

• Page 529.

EM WavesEM Waves

• Radio Waves

• Infrared Radiation

• Visible Radiation- only part of spectrum we can see.

• Ultraviolet Radiation –

• X-Rays and Gamma Rays

Light FactsLight 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.

AbsorbedAbsorbed

• Light that is absorbed is taken in by the

matter it strikes.• Black objects absorb

all light-best color for absorption.

ReflectedReflected

• Light that is reflected bounces off the substance it strikes.

• Example: Mirrors

Transmitted LightTransmitted 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.

ReflectionReflection

• 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.

RefractionRefraction

• 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. It is not refracted.

What is the spectrum?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?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?What color do you see?

• Concave Mirror Focuses Colors          Concave Mirror Focuses Colors         

                                                      

       

Opaque ObjectsOpaque 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 ObjectsTransparent 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?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 typesTwo main typesof lensesof 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 lensConcave 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?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?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: 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   Convex Lens is Inverse     of Concave Lens                   of Concave Lens                

• Convex Lens is Inverse     of Concave Lens                

Convex Lens is Inverse     of Concave Lens                

                                      

       

• Image Formation with Lenses If object isfar from thelens (beyond)the focal point, a realinverted imageis formed