Physics Exam 3 LSU: Chapter 26

List the 7 conventions used for a single lens

1.) The object is placed to the left of the lens 2.) Real images fall to the right of the lens 3.) Virtual images fall to the left of the lens 4.) The object distance is always positive 5.) The image distance is positive for real images and negative for virtual images 6.) The focal length is positive for converging lens and negative for diverging lens 7.) The magnificaiton is positive for an upright image and negative for an inverted image

Light rays with incident angles exceeding _________ for a water-air interface yield no refracted light, and the light is totally reflected back into the medium

48.8 degrees

The image is of the entire object, although its brightness is reduced since fewer rays produce it. The amount of light which passes through the lens is reduced by a factor of two when half of the lens is covered with black tape. Therefore, the image is of the entire object, although its brightness is reduced since fewer rays produce it.

A converging lens is used to produce a real image, as in the figure. A piece of black tape is then placed over the upper half of the lens. Which one of the following statements is true concerning the image that results with the tape in place?

The greater the refraction index of a color, the ____________ it will bend

Greater

Describe the image formed by a converging lens when the object is located at a distance from the lens that is between the focal length and twice the focal length

Image is --Inverted --Real --Larger than Object

Describe the image formed by a converging lens when the object is located at a distance from the lens that is between the focal point and the lens?

Image is: --Upright --Virtual --Larger than Object

Regardless of the position of a real object, what does the image formed by a diverging lens always look like??

Image is: --Upright --Virtual --Smaller than the object

Describe the image formed by a converging lens when the object is located at a distance from the lens that is greater than twice the focal length

Image: --Inverted --Real --Smaller than the object

What is the overall magnification of a two lens system?

It is the product of the magnifications of the two lenses.

If n1> n2 what does this mean?

It means that then SinTheta2>Sintheta1 and Theta2>Theta1. This means that the ray is bent AWAY from the normal.

If n1 < n2 what does this mean?

It means that then Sintheta2 < sintheta1 and theta2<theta1 This means that the ray is bent TOWARD the normal.

Two rays of light converge to a point on a screen. A thick plate of glass with parallel surfaces is placed in the path of this converging light, with the parallel surfaces parallel to the screen. What is true about the point of convergence? It moves away from the glass plate. It moves toward the glass plate. It will remain on the screen.

It moves away from the glass plate. Since the index of refraction of glass is greater than the index of refraction of air, when the two rays of light emerge from the glass, they will be farther apart than they would have been if the plass plate were not present. Since they are farther apart than they would have been, a longer distance will be required for them to converge. Therefore, the point of convergence will move away from the glass plate.

When light strikes the interface between two transparent materials, such as air and water, the light generally divides into two parts. Part of the light is reflected, with the angle of reflection equaling the angle of incidence. The remainder is transmitted across the interface. If the incident ray does not strike the interface at normal incidence, the transmitted ray has a different direction than the incident ray.

Just read this and absorb it.

A shallow swimming pool has a constant depth. A point source of light is located in the middle of the bottom of this pool and emits light in all directions. However, no light exists the surface of the water except through a relatively small circular area that is centered on and directly above the light source. Why does the light exit the water through such a limited area?

Light reaching the surface of the water outside the circular area is totally internally reflected. The critical angle for a water-air interface is 48.8 degrees. Any light emitted at an angle greater than this with respect to the vertical is incident on the surface at an angle exceeding the critical angle. It is totally internally reflected and doesn't exit the water.

When an observer peers over the edge of a deep, empty, metal bowl on a kitchen table, he does not see the entire bottom surface. Therefore, a small object lying on the bottom is hidden from view, but the object can be seen when the bowl is filled with liquid A. When the bowl is filled with liquid B, however, the object remains hidden from view. Which liquid has the greater index of refraction?

Liquid A. Liquid A has the greater index of refraction because the light bends more. The greater the index of refraction, the more the light bends.

What is the sign of the image distance for an image (virtual) formed to the left of the lens?

Negative

What is the sign of the object distance if the object is to the right of the lens (virtual object)?

Negative

When light is incident at the Brewster angle, the reflected and refracted rays are ___________ to each other.

Perpendicular

What is the sign of the image distance for am image (real) formed to the right of the lens?

Positive

What is the sign of the magnification for an image that is upright with respect to the object?

Positive

What is the sign of the object distance if the object is to the left of the lens (real object)?

Positive

What is the sign of the focal length for a converging lens? Diverging?

Positive for converging Negative for diverging

Describe the ray tracing procedure for a converging lens.

Ray 1: Parallel to axis, through lens, through focal point on other side Ray 2: Through near focal point, through lens, and then parallel to axis. Ray 3: Through center of lens, no bending.

No. By applying Snell's law at both surfaces of the glass slab and using Equation 26.4, one can determine that the angle of incidence at the second surface will always be less than the critical angle. Therefore, the ray within the glass will never experience total internal reflection.

Refer to Figure. Note that the ray within the glass slab is traveling from a medium with a larger refractive index toward a medium with a smaller refractive index. Is it possible, for θglass the angle of incidence at the first surface less than 90 degrees, that the ray within the glass will experience total internal reflection at the glass-air interface?

How does the critical angle fit into snells law?

The angle of incidence θ1 is related to the angle of refraction θ2 by Snell's law, where θ2 is part of the right triangle in the drawing. The critical angle θc for the core-cladding interface is also part of the same right triangle, so that θ2 = 90° − θc.

What is refraction?

The change in speed as a ray of light goes from one material to another causes the ray to deviate from its original direction. This change in direction is refraction. --When a light beam bends either towards or AWAY from the surface normal --this bent beam is called the refracted beam

It is totally internally reflected, no matter what the surrounding liquid is. The angle of incidence when ray B reaches the hypotenuse is greater than the angle of incidence when ray A reaches the hypotenuse. Therefore, ray B will be totally internally reflected because the angle of incidence is greater than the critical angle.

The drawing shows 30o-60o-90o a prism and two light rays, A and B, which both strike the prism perpendicularly. The prism is surrounded by an unknown liquid, which is the same in both parts of the drawing. When ray A reaches the hypotenuse in the drawing, it is totally internally reflected. Which one of the following statements applies to ray B when it reaches the hypotenuse?

Liquid B. When passing from a material with a larger index of refraction into a material with a smaller index of refraction, the light will bend away from the normal line. Therefore, the index of refraction of liquid A is greater than the index of refraction of liquid B. When passing from a material with a smaller index of refraction into a material with a larger index of refraction, the light will bend toward the normal line. Therefore, the index of refraction of liquid B is smaller than the index of refraction of liquid C. Therefore, liquid B has the smallest index of refraction.

The drawing shows three layers of liquids, A, B, and C, each with a different index of refraction. Light begins in liquid A, passes into B, and eventually into C, as the ray of light in the drawing shows. The dashed lines denote the normals to the interfaces between the layers. Which liquid has the smallest index of refraction?

Describe the relationship between the index of refraction and the bending of light.

The greater the index of refraction, the more the light bends.

In a multi lens system, what is the object for the next lens?

The image produced by one lens serves as the object for the next lens.

As the angle of incidence increases, the angle of refraction ____________

increases

A man is fishing from a dock. He is using a bow and arrow. To strike a fish that he sees beneath the water, where should he aim?

somewhat below the fish Since the index of refraction of water is greater than the index of refraction of air, the fish appears to be above where it is actually located. So, the man should aim somewhat below the fish.

You are sitting by the shore of a lake on a sunny and windless day. When are your Polaroid sunglasses most effective in reducing the glare of the sunlight reflected from the lake surface? When the angle of incidence of the sunlight on the lake is ____________ 0 degrees because the sun is directly overhead almost 90 degrees because the sun is low in the sky somewhere between 90 and 0 degrees

somewhere between 90 and 0 degrees When the angle of incidence is the Brewster angle, the reflected light is completely polarized. Therefore, when the angle of incidence of the sunlight on the lake is somewhere between 90 and 0 degrees, the Polaroid sunglasses will be most effective.

When the angle of incidence reaches a certain value, called the critical angle θc, what is the angle of refraction?

the angle of refraction is 90°. Then the refracted ray points along the surface

What is the index of refraction (n)?

the index of refraction of a material is the ratio of the speed c of light in a vacuum to the speed v of light in the material: n=Speed of light in a vacuumSpeed of light in the material=cv

What happens when unpolarized light strikes a nonmetallic surface at the Brewster angle?

the reflected light is 100% polarized in a direction parallel to the surface. The angle between the reflected and refracted rays is 90°.

When light travels FROM a medium where the refractive index is LARGER into a medium where it is SMALLER, which direction is the refracted ray bent?

the refracted ray is bent AWAY from the normal

When light travels FROM a medium where the refractive index is SMALLER into a medium where it is LARGER, which direction is the refracted ray bent??

the refracted ray is bent TOWARD the normal

When the angle of incidence exceeds the critical angle, what happens?

there is no refracted light. All the incident light is reflected back into the medium from which it came, a phenomenon called total internal reflection.

A swimmer is treading water (with her head above the water) at the surface of a pool 3.00 m deep. She sees a coin on the bottom directly below. How deep does the coin appear to be?

use the equation for apparent depth to get 2.26 m. you have to remember that the light rays travel from the coin to the swimmer. Therefore, the incident ray is coming from the coin under the water (n1 = 1.33), while the refracted ray is in the air (n2 = 1.00).

How do we label all variables associated with the incident and reflected ray? The refracted ray?

we label all variables associated with the incident (and reflected) ray with subscript 1 and all variables associated with the refracted ray with subscript 2. So Incident or reflected ray: Subscript 1 Refracted ray: subscript 2

Figure 26.5 shows two rays of light leaving a point P on the coin. When the rays enter the water, they are refracted toward the normal because water has a larger index of refraction than air has. By extending the refracted rays backward (see the dashed lines in the drawing), we find that they appear to originate from a point P′ on a virtual image, which is what the swimmer sees. Answers (b) and (c) are incorrect. These answers are incorrect because the point P′ in Figure 26.5 is located at a height that is greater than, not less than or the same as, the actual height of the coin. Answer (a) is correct. The point P′ in Figure 26.5 is on a virtual image that is located at an apparent height d′ that is greater than the actual height d. Equation 26.3 [d′ = d (n2/n1)] reveals the same result, because n1 represents the medium (air) associated with the incident ray and n2 represents the medium (water) associated with the refracted ray. Since n2 for water is greater than n1 for air, the ratio n2/n1 is greater than one and d′ is larger than d. This situation is the opposite of that in Figure 26.4b, where an object beneath the water appears to a person above the water to be closer to the surface than it actually is.

A swimmer is under water and looking up at the surface. Someone holds a coin in the air, directly above the swimmer's eyes. To the swimmer, the coin appears to be at a certain height above the water. Is the apparent height of the coin (a) greater than, (b) less than, or (c) the same as its actual height?

A beacon in a lighthouse is to produce a parallel beam of light. The beacon consists of a light source and a converging lens. Where should the light source be placed?

At the focal point of the lens. According to the principle of reversibility, if the light source is placed at the focal point of the lens, then the light rays will be parallel after they pass through the lens.

How do you determine the location of the final image in a multi lens system??

By applying the thin lens equation to each lens separately

What is a converging lens?

Causes incident parallel rays to converge at the focal point. Thicker at the center than at the edges

What is a diverging lens??

Causes incident parallel rays to diverge after exiting the lens Thinner at the center than at the edges, so thicker at the edges

Two identical containers, one filled with water (n = 1.33) and the other with benzene (n = 1.50) are viewed from directly above. Which container (if either) appears to have a greater depth of fluid?

The one filled with water. The apparent depth of a fluid is inversely proportional to the index of refraction of the fluid. Therefore, the container filled with water will appear to have the greater depth because the index of refraction of water is smaller than the index of redraction of benzene.

What happens when light strikes a nonmetallic surface at an angle of incidence equal to the Brewster angle??

The reflected light will be totally 100% polarized parallel to the surface. The light transmitted through the surface, that is the refracted light, is then PARTIALLY polarized PERPENDICULAR to the surface.

What is dispersion?

The spreading of light into its color components

Describe the relationship between apparent depth and the index of refraction.

They are inversely proportional. So if a material has a larger index of refraction, it will have a smaller apparent depth.

Total internal reflection occurs only when what conditions are met?

Total internal reflection occurs only when light travels from a HIGHER-index medium toward a LOWER-index medium. The refracted ray is then bent AWAY from the normal It does not occur when light propagates in the reverse direction—for example, from air to water.

True or false. For incident angles other than 0°, unpolarized light becomes partially polarized in reflecting from a nonmetallic surface,

True

True or false?Total internal reflection occurs only when the beam of light has an angle of incidence that is greater than the critical angle θc.

True

Slab B. Since the slab with the greater index of refraction bends the light through a greater angle, slab B has the greater index of refraction.

Two slabs with parallel faces are made from different types of glass. A ray of light travels through air and enters each slab at the same angle of incidence, as the drawing shows. Which slab has the greater index of refraction?

A diamond gemstone is famous for its sparkle in air because the light coming from it glitters as the diamond is moved about. The sparkle is related to the total internal reflection of light that occurs within the diamond. What happens to the sparkle when the diamond is placed under water? (a)Nothing happens, for the water has no effect on total internal reflection. (b)The water reduces the sparkle markedly by making the total internal reflection less likely to occur.

When a diamond is held in a certain way in air, the intensity of the light coming from within it is greatly enhanced. Figure 26.10 helps to explain that this enhancement or sparkle is related to total internal reflection. Part a of the drawing shows a ray of light striking a lower facet of the diamond at an angle of incidence that exceeds the critical angle for a diamond-air interface. As a result, this ray undergoes total internal reflection back into the diamond and eventually exits the top surface. Since diamond has a relatively small critical angle in air, many of the rays striking a lower facet behave in this fashion and create the diamond's sparkle. Part (a) of Example 5 shows that the critical angle is 24.4° and is so small because the index of refraction of diamond (n = 2.42) is large compared to that of air (n = 1.00). Answer (a) is incorrect. The water does indeed have an effect on the total internal reflection that occurs. This is because the critical angle depends on the index of refraction of the water as well as that of the diamond Answer (b) is correct. Figure 26.10b illustrates what happens to the same ray of light within the diamond when the diamond is surrounded by water. Because water has a larger index of refraction than air does, the critical angle for the diamond-water interface is no longer 24.4° but increases to 33.3°, as part (b) of Example 5 shows. Therefore, this particular ray is no longer totally internally reflected. As Figure 26.10b indicates, only some of the light is now reflected back into the diamond, while the remainder escapes into the water. Consequently, less light exits from the top of the diamond, causing it to lose much of its sparkle.

What is snells law of refraction?

When light travels from a material with refractive index n1 into a material with refractive index n2, the refracted ray, the incident ray, and the normal to the interface between the materials all lie in the same plane. The angle of refraction θ2 is related to the angle of incidence θ1 by n1 sin θ1=n2 sin θ2

Is it possible for a lens to behave as a converging lens when surrounded by air but to behave as a diverging lens when surrounded by another medium?

Yes Since whether the light bends toward or away from the principal axis is determined in part by the index of refraction of the surrounding medium, it is possible for a lens to behave as a converging lens when surrounded by air but to behave as a diverging lens when surrounded by another medium.

Can speed of a light ray be less than C? (3.00 x 10^8)

Yes, like if it passes through a surface after being in a vaccumm. BUT IT CAN NEVER BE GREATER THAN C

Light traveling through air is incident on a flat piece of glass at a 35° angle of incidence and enters the glass at an angle of refraction θglass. Suppose that a layer of water is added on top of the glass. Then the light travels through air and is incident on the water at the 35° angle of incidence. Does the light enter the glass at the same angle of refraction θglass as it did when the water was not present?

Yes. By applying Snell's law at the air-water interface and at the water-glass interface, one can determine that the light enters the glass at the same angle of refraction.

A man is fishing from a dock. He is using a laser gun that emits an intense beam of light. To strike a fish that he seems beneath the water, where should he aim?

directly at the fish. Since the laser beam will refract when it crosses the air-water interface, he should aim directly at the fish.

What is apparent depth?

consequence of refraction is that an object lying under water appears to be closer to the surface than it actually is. basically an observer sees a virtual image at an apparent depth that is less than that of the actual depth If the observer is directly above (or below) the object, the apparent depth is related to the actual depth by this equation.