Light

Chapter 18

Chapter 18

Section 1 - Light and Color

When light strikes an object, the light ca be reflected, transmitted, or absorbed.

Transparent - a material that transmits most of the light that strikes it

Translucent - a material that scatters light as it passes through

Opaque - a material that reflects or absorbs all of the light

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Light and Color

The color of an object depends on the object’s material and the color of the light striking the object.Every object absorbs some wavelengths of light and reflects others.The color of an opaque object is the color of the light it reflects.The color of a transparent or translucent object is the color of the light it transmits.

Chapter 18

Light and Color

Primary colors – three colors that can combine to make any other color– red, green , blue

Secondary colors – produced when two primary colors combine in equal amounts– magenta, yellow, and cyan

White light – produced when the three primary colors are combined in equal amounts.

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Light and Color

Complementary colors – any two colors that combine to form white light.Pigments – colored substances that are used to color other materials– As pigments are added together, fewer

colors of light are reflected and more absorbed.

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Section 2 - Reflection and Mirrors

light rays represent light waves as straight linesThe two ways in which a surface can reflect light are regular reflection and diffuse reflection pg.618Regular – when parallel rays of light hit a smooth surfaceDiffuse - when parallel rays of light hit a bumpy or uneven surface

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Reflection and MirrorsPlane Mirror

Plane mirror – a flat sheet of glass that has a smooth, silver-colored coating on one side

image - copy of an object formed by reflected or refracted rays of light

produces a virtual image– right side up– the same size as the object being reflected– behind the mirror

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Reflection and MirrorsConcave Mirrors

Surface curves inward like a bowl– used for make-up mirrors

Optical Axis – an imaginary line that divides a mirror in half (equator)

Focal Point – the point at which rays parallel to the optical axis meet.

Ray Diagram

Forms either a virtual image or real image (pg. 621)

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Reflection and MirrorsConcave Mirrors

Real Image – forms when rays actually meet– Upside down– Larger or smaller than the object

Image– Real - farther than the focal point

• In front and upside down

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Reflection and MirrorsConcave Mirrors

Image (Cont’d)– Virtual - Closer than the focal point

• Behind and upright

At the focal point - no image is formed– Forms parallel light rays– Headlights

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Reflection and MirrorsConvex Mirrors

Surface curves outward.

Forms a smaller virtual image (pg. 622)– used for security or blind spots on roads

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Section 3 - Refraction and Lenses

When light rays enter a medium at an angle, the change in speed causes the rays to bend, or change direction– Two images in fish tank

index of refraction - a measure of how much a ray of light bends when it enters that material (pg. 624)

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Refraction and Lenses

Prisms and Rainbows– Longer wavelengths (red) refracted less– Shorter wavelengths (violet) refracted more– Separates the colors of white light

mirage - an image of a distant object caused by refraction of light (by hot air)Lens – a curved piece of glass or other transparent material that is used to refract light

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Convex lens

Thicker in the center than at the edges

parallel light rays are bent towards the center of the lens (pg. 626)

forms virtual or real image dependent upon position relative to the focal point

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Concave lenses

Thicker at the edges than in the center

parallel light rays are bent away from the center of the lens (pg. 627)

forms virtual image (again because rays can never meet)

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Section 4 - Seeing Light

You see an object when a process occurs that involves both your eyes and your brain.

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Section 4 - Seeing Light

Eye picture pg. 631– cornea -– pupil -– iris -– lens -– retina -– optic nerve -

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Seeing Light

nearsighted - can see close objects clearly – eyeball too long.– corrected with concave lens

Farsighted - can see far away objects clearly

– eyeball too short. – Corrected with convex lens

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Section 5 - Using Light

Optical Instruments– Telescope uses lenses or mirrors to collect

and focus light from distant objects.– Images are upside-down

• Refracting telescope– Objective– Eyepiece

• Reflecting

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Using Light

Optical Instruments– (Light) Microscope – uses a combination of

lenses to produce and magnify an image– Camera – use a lens to focus light to form

a real, upside-down image on the back of the (film) camera

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Using Light

– Lasers• Light amplification by stimulated emission of

radiation• Laser light consists of light waves that all have

the same wavelength, or color. The waves are coherent, or in step.

• Uses– Compact discs– Holography– Surgery

Chapter 18

Using Light

– Optical Fibers – long, thin strands of glass or plastic that can carry light for long distances without allowing the light to escape.

• Total internal reflection – complete reflection of light by the inside surface of the medium

• Medicine• Communication