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Section 1 Mirrors and Lenses

Rays and the Path of Light Waves

Because light waves travel in straight lines, you can use an arrow called a ray to show the path and the direction of a light wave. Rays help to show the path of a light wave after it bounces or bends.

Chapter 23



Mirrors and Reflection of Light

•A plane mirror is a mirror that has a flat surface.

•The reflection of an object in a plane mirror is right side up and the same size as the object, but reversed left to right.

• Plane mirrors form virtual images. A virtual image is an image through which light does not travel

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Section 1 Mirrors and LensesChapter 23



Mirrors and Reflection of Light, continued

•A concave mirror is a mirror that is curved inward.

• The image formed by a concave mirror depends on the optical axis, focal point, and focal length of the mirror.

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• A real image is an image through which light passes.

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How Images Are Formed in Concave Mirrors




• Convex Mirrors A convex mirror is a mirror that curves outward.

• The image formed by a convex mirror is always virtual, right side up, and smaller than the original object.

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Lenses and Refraction of Light

• A lens is a transparent object that forms an image by refracting, or bending, light. Two kinds of lenses are convex and concave.

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Lenses and Refraction of Light, continued

• Convex Lenses A convex lens is thicker in the middle than at the edges.

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Lenses and Refraction of Light, continued

• Concave Lenses A concave lens is thinner in the middle than at the edges.

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Section 2 Light and Sight

How You Detect Light

• Your eye gathers visible light to form the images that you see.

• The thickness of the lens of the eye changes so that objects at different distances can be seen in focus. The light that forms a real image on the retina is detected by receptors called rods and cones.

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Section 2 Light and SightChapter 23



Common Vision Problems

• Nearsightedness happens when a person’s eye is too long. A nearsighted person can see something clearly only if it is nearby. Faraway objects look blurry.

• Farsightedness happens when a person’s eye is too short. A farsighted person can see faraway objects clearly. But things that are nearby look blurry.

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Common Vision Problems, continued

• The images below explain how nearsightedness and farsightedness can be corrected with glasses.

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Common Vision Problems, continued

• Color Deficiency is another name for colorblindness. The majority of people who have color deficiency can’t tell the difference between shades of red and green or can’t tell red from green.

• Color deficiency happens when the cones in the retina do not work properly. Color deficiency cannot be corrected.

Chapter 23



Surgical Eye Correction

• Surgical eye correction works by reshaping the patient’s cornea by using a laser. Patients often gain perfect or nearly perfect vision after surgery.

• Risks of Surgical Eye Correction Some patients report glares, double vision, or trouble seeing at night. People under 20 years old should not have surgical eye correction because their vision is still changing.

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• Optical instruments are devices that use mirrors and lenses to help people make observations.

• Cameras A camera is used to record images. All cameras have a lens, shutter, and an aperture.

• A 35 mm camera records images on film. A digital camera uses light sensors to record images and to send electric signals to a computer.

Chapter 23 Section 3 Light and Technology

Optical Instruments


Optical Instruments, continued

• Telescopes Telescopes are used to see detailed images of large, distant objects.

•Refracting telescopes use lenses to collect light.

•Reflecting telescopes use mirrors to collect light.



Optical Instruments, continued

• Light Microscopes Microscopes are used to study tiny, nearby objects.

• Microscopes have two convex lenses. An objective lens is close to the object being studied. An eyepiece lens is in the lens you look through.



Lasers and Laser Light

• A laser is a device that produces intense light of only one wavelength and color.



Lasers and Laser Light, continued

• Uses for Lasers Lasers are used to make holograms. A hologram is a piece of film that produces a three-dimensional image of an object.

• Lasers have many other applications. They are used to cut materials such as metal and cloth. Doctors sometimes use lasers for surgery. CD players use lasers to read CDs.



Optical Fibers• An optical fiber is a thin, glass wire that transmits light over long distances.

•Optical fibers are used to transmit information through telephone cables and network computers. Doctors use optical fibers to see inside patients’ bodies.

•Light in a Pipe Optical fibers are like pipes that carry light. Light stays inside an optical fiber because of total internal reflection, the complete reflection of light along the surface of the material.



Polarized Light

• Polarized light consists of light waves that vibrate in only one plane.

•Some sunglasses and camera lenses use polarized filters to reduce glare.



Communication Technology

• Light waves, radio waves, and microwaves are all types of electromagnetic waves. Cordless telephones and cellular telephones use radio waves and microwaves to send signals.

• Cordless Telephones The base of a cordless telephone changes the signal it receives into radio waves. The handset changes the radio waves into sound.



Communication Technology, continued• Cellular Telephones Cellular telephones send and receives signals from distant towers. Instead of using radio waves like cordless phones, cellular phones use microwaves to send information.

• Satellite Technology Microwave signals are broadcast from space to satellite dishes on Earth.

• Satellites allow more people to receive the signals and to receive higher quality signals than if antennas on Earth were used.

• The Global Positioning System The GPS is a network of 27 satellites that orbit Earth. A GPS receiver receives signals from at least four satellites to find its exact location.


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