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19.2 Lenses
Lenses
What causes light to refract?
When light enters a new medium at an angle, the change in speed causes the light to bend, or refract.
In what types of materials is total internal reflection likely to occur?
19.2 Lenses
Light rays ________ and _______ as they pass through the curved glass lens. In this case, the result is a magnified image.
slow
bend
19.2 Lenses
Light usually travels in straight lines. In a vacuum, light travels at a speed of _______________meters per second.
• ________ allows light to pass through almost as fast as it would through a vacuum.
• The speed of light __________ when it goes through different types of media.
Index of Refraction of Light
3.00 x 108
Air
varies
19.2 Lenses
The speed of light in water is __________ meters per second. The speed of light in glass is ___________ meters per second.
• When light passes from air into glass or water, it _________ down and is ___________.
• When light passes from glass or water into air, it ___________ up and is bent back to its original ________________.
Index of Refraction of Light2.25 x 108
2.00 x 108
slows refracted
speedsdirection
19.2 Lenses
A light ray ________ (refracts) as it passes through different types of media.
The ray again travels in its original direction when it reenters the _______.
Index of Refraction of Light
bends
air
19.2 Lenses
The amount of refraction depends upon the difference between the speeds of light in the two media. The ____________________for a material is the ratio of the speed of light in a vacuum to the speed of the light in the material.
• A ______ index of refraction (near 1) causes light to slow and refract very little such as _______.
• ___________ (index of refraction = 2.42), causes significant refraction.
Index of Refraction of Light
index of refraction
low
air
Diamond
19.2 Lenses
Concave Lenses
A lens is an object made of transparent material that has one or two curved surfaces that can __________ light.
A concave lens is curved __________ at the center and is __________ at the outside edges.
Concave and Convex Lenses
refract
inwardthickest
Focal point
Concave lens
Optical axis
19.2 Lenses
When parallel incoming rays strike a concave lens, they are ____________ away from one another.
Concave and Convex Lenses
refracted
Focal point
Concave lens
Optical axis
19.2 Lenses
As the light rays diverge after passing through the concave lens, they form a __________ image of the object.
Concave and Convex Lenses
Focal point
Concave lens
Focal point Virtual image
Object
virtual
19.2 Lenses
Concave lenses are often used in the viewfinders of ____________. Concave lenses are also combined with mirrors or other lenses to form images in optical instruments such as ______________.
Concave and Convex Lenses
cameras
telescopes
19.2 Lenses
Convex Lenses
A convex lens is curved __________ at the center and is ___________ at the outer edges.
• As the rays pass through the lens, each one is refracted, and they emerge at ____________ angles.
• Convex lenses cause incoming parallel rays to come together, or _____________.
Concave and Convex Lenses
outward
thinnest
Focal point
Optical axis
Convex lens
different
converge
19.2 Lenses
• The converging rays meet at the focal point, on the side of the lens ____________ to the object.
• When an object is located beyond the focal point, a _________ image is formed and is ___________ than the original object.
Concave and Convex Lenses
real
opposite
Focal point
Convex lens
Focal point
Real image
Object
smaller
19.2 Lenses
A magnified, __________ image is formed when the object is located between the focal point and the lens.
Concave and Convex Lenses
Focal point
Convex lens
Focal point Object
Virtual image
Focal point
virtual
19.2 Lenses
Each of the housefly’s eyes is made up of thousands of tiny individual eyes called facets.
The outer surface of each facet is _________. The eyes give the fly a nearly 360-degree field of view.
Concave and Convex Lenses
convex
19.2 Lenses
Convex lenses are used in _________ and __________ projectors and cameras.
At the movie theatre, the film is placed _________ _________ in the projector so that the real image is upright.
Concave and Convex Lensesslide
movie
upside down
19.2 Lenses
In the past, lighthouses used a light source placed at the _________ point of a convex lens or series of convex lenses to form a beam of parallel light rays.
Concave and Convex Lenses
focal
19.2 Lenses
The critical angle is the angle of incidence that produces an angle of refraction of ____ degrees.
• For angles less than the critical angle, light is partly ____________ and partly reflected.
• At the critical angle, the light ray bends so much that it takes a ________ along the glass-air boundary.
Total Internal Reflection
90
path
refracted
19.2 Lenses
Total internal reflection is the complete ___________ of a light ray back into its original medium.
Total Internal Reflection
reflection
19.2 Lenses
An important application of total internal reflection is _________ ___________.
• Light rays are generally unable to exit through the sides of the curving fiber optic strands.
• Fiber optics are able to transmit data in the form of __________ pulses over large distances with little loss in signal strength.
Total Internal Reflection
fiber optics
light
19.2 Lenses
Assessment Questions
1. Light refracts when it passes from air to water because a. the wavelength is different in the two media.
b. the frequency is different in the two media.
c. the speed is different in the two media.
d. the amplitude is different in the two media.
19.2 Lenses
Assessment Questions
2. Which type(s) of lens can form a real image? a. concave lens onlyb. convex lens onlyc. both concave and convex lensesd. neither concave nor convex lenses
19.2 Lenses
Assessment Questions
3. What will happen to a ray of light if it hits a new medium at an angle greater than the critical angle? a. All the light will be refracted.
b. Part of the light will be refracted and part reflected.
c. All the light will be reflected.
d. All the light will be absorbed.
19.2 Lenses
Assessment Questions
4. The index of refraction is the ratio of the speed of light in a vacuum to the speed of light in a material.
TrueFalse
