1. 18.5 Using Light Pg

2. Optical Instruments
There are three common types of optical instruments:
1. Telescope – helps you see far away objects
2. Microscopes – helps you see nearby objects
3. Cameras

3. Telescopes
Distant objects are difficult to see because light from them has spread out by the time they reach your eyes
Telescopes form enlarged images of distant objects
Use lenses or mirrors to collect and focus light from distant objects

4. Types of Telescopes There are two types of telescopes
1. Refracting Telescopes
2. Reflecting Telescopes

5. Refracting Telescopes
Refracting Telescopes consists of two convex lenses, one at each end of the tube
the larger lens is called the objective
Gathers the lighting coming from an object and focuses the rays to form a real image
The lens close to your eye is called the eyepiece
Magnifies the image so you can see it clearly

6. Reflecting Telescope
Reflecting Telescopes use a large concave mirror to gather light
The mirror collects light from distant objects and focuses the rays to form a real image
A small mirror inside the telescope reflects the image to the eyepiece
The images you see are upside down

7. Microscopes
Microscopes are optical instruments that form enlarge images of tiny objects
Microscopes use a combination of lenses to produce and magnify an image
Example: Figure 23.
Two convex lenses are used to magnify the specimen
The objective forms a real, enlarged image
The eyepiece enlarges the image even more

9. Cameras
Cameras use one or more lenses to focus light and film to record an image
Light travels from an object, travels to the camera and passes through the lens
The lens of a camera focuses light to form a real, upside-down image on film in the back of the camera
In most cameras the lens will move closer to or away from the film until the image is focused

10. How to Take a Picture To take a photo:
Press a button that briefly opens the shutter, a screen in front of the film
Light passes through the lens to hit the film
The diaphragm is a device with a hole that can be made smaller or larger
Changing the size of the hole controls how much light hits the film

12. Lasers
Laser light consists of light waves that all have the same wavelength, or color
The light waves from lasers are coherent, or in step
All of the crests of the waves align with one another

14. What is a Laser?
A laser is a device that produces a narrow beam of coherent light
Light
Amplification by
Stimulated
Emission of
Radiation

15. What is a Laser? Light amplification means that light is strengthened
Stimulated emission means that the atoms emit light when exposed to electromagnetic radiation

16. Producing Laser Light Figure 26. pg 636
The laser tube contains a mixture of helium and neon gases
An electric current causes the gas mixture to emit photons (a packet of light energy)
Mirrors at both ends of the tube reflect photons back and forth
Photons bump into neon particles
Neon particles emit photons with the same energy as the one that caused the collision

17. Producing Laser Light
The two photons travel together in step with one another
Process continues until there is a stream of in step photons traveling up and down the tube
Some light leaks through the partially reflecting mirror.
This light is the laser

18. Uses of Lasers Lasers have many practical uses
Stores use lasers to scan barcodes
Engineers use lasers to make sure surfaces are level and bridges and tunnels are properly aligned
Lasers are also used to read information on compact discs, create holograms, and perform surgery

19. Compact Discs Lasers can be used to store and read information
Compact discs are created by converting data into electrical signals
Electrical signals are used to control a laser beam, which cuts patterns of pits into blank discs
Lasers also used when you play compact discs
Laser beams shines on the disc and is reflected

21. Holography Videos and books may have pictures that appear to move
Holograms are three dimensional photographs created by using the light from a laser beam
The process of making holograms is called holography

22. Laser Surgery
A beam of laser light can be powerful enough to replace a knife
As a laser cuts it seals blood vessels
Reduces the amount of blood a patient loses
Wounds from surgery heal faster
Used to remove skin blemishes or cancerous growths

23. Laser Surgery: Vision
A common laser surgery is to correct vision by reshaping the cornea
Lasers can also be used to repair detached retinas
Detached retinas can lead to partial or total blindness because the cones and rods can no longer send signals to the brain
Lasers weld/burn the retina back into the eyeball

24. Optical Fibers Laser beams can carry signals from one place to another
Laser beams are sent through optical fibers
Optical fibers are long, thin strands of glass or plastic that can carry light for long distances without letting the light escape

25. Optical Fibers
Optical fibers can carry laser beams long distances because the beam stays total inside the fiber as it travels
The angle of incidence determines whether or not light passes through the surface

26. Total Internal Reflection
The complete reflection of light by the inside surface of a medium is called total internal reflection (Fig. 29 pg. 640)
Each time, the light ray strikes the side of the optical fiber, the angle of incidence is large
Because the angle is large the light ray is always completely reflected
NO LIGHT CAN ESCAPE THROUGH THE SIDE OF THE OPTICAL FIBER!

27. Medicine Optical fibers are commonly used in medicine
Can be placed inside the body and then attached to a camera or computer
Doctor can see internal organs without performing major surgery
Often used to repair damage to joints
Allows less damage to the knee
Tissues recover easier

28. Communications
Optical fibers have led to great improvements in telephone service, computer networks, and cable television systems
Signals sent over optical fibers are much faster and clearer than those sent over copper wire
Example: One tiny optical fiber can carry thousands of phone conversations at the same time