MisConceptual Ch.23

You want to create a spotlight that will shine a bright beam of light with all of the light rays parallel to each other. You have a large concave spherical mirror and a small light bulb. Where should you place the lightbulb? a) at the focal point of the mirror b) at the radius of the curvature of the mirror c) at any point, because all rays bouncing off the mirror will be parallel d) none of the above; you can't make parallel rays with a concave mirror

A) When a light rays which are parallel to each other are passed through the concave spherical mirror, they will reflect from the mirror through a focal point. Thus the light bulb must be placed at the focal point to create a spotlight that will shine a bright beam of light.

When the reflection of an object is seen in a flat mirror, the image is a) real and upright b) real and inverted c) virtual and upright d) virtual and inverted

C) the image of an object seen in the flat mirror is on the other side of the mirror so it is virtual in nature and is upright

Virtual images can be formed by a) only mirrors b) only lenses c) only plane mirrors d) only curved mirrors or lenses e) plane and curved mirrors and lenses

Virtual images can be formed by plane mirrors, curved mirrors both convex and concave. Both the convex and concave lenses are diverging and converging in nature

As an object moves from just outside the focal point of a converging lens to just inside it, the image goes from ___ and ___ to ___ and ___. a) large; inverted; large; upright b) large; upright; large; inverted c) small; inverted; small; upright d) small; upright; small; inverted

a) The image produced by a converging lens varies as object distance varies. When the object is outside the focal point of a converging lens, then the image is always real and inverted. However, the object moves inside the focal point the image is virtual and upright. IF the object is closer to the focal point, the image is enlarged. Thus, moving from the outside of the focal point to the inside position, the image goes from large inverted to the large upright

To shoot a swimming fish with an intense light beam from a laser gun, you should aim a) directly at the image b) slightly above the image c) slightly below the image

a) directly at the image?

Suppose you are standing about 3m in front of a mirror. You can see yourself just from the top of your head to your waist, where the bottom of the mirror cuts off the rest of your image. If you walk one step closer to the mirror a) you will not be able to see any more of your image b) you will be able to see more of your image, below your waist c) you will see less of your image, with the cutoff rising to be above your waist

a) you will not be able to see any more of your image When moving one step closer to the mirror, we will see the same amount of image. The size of the image within the mirror exists within relation to to the size of the mirror. When moving farther from the mirror, the mirror will also get proportionally smaller. As you move closer towards the mirror, the greater the incident and reflected angle will be, but the rays will be reflected at the same points.

When moonlight strikes the surface of a calm lake, what happens to the light? a) all of it reflects from the water surface back to the air b) some of it reflects back to the air; some enters the water c) all of it enters the water d) all of it disappears via absorption by water molecules

b) If all the light is reflected from the surface, the lake will appear dark. As we can see the moon light under the water means that some of the light is reflected off the surface and some parts have entered into the water.

You cover half of a lens that is forming an image on a screen. Compare what happens when you cover the top half of the lens versus the bottom half. a) when you cover the top half of the lens, the top half of the image disappears; when you cover the bottom half fo the lens, the bottom half of the image disappears b) when you cover the top half of the lens, the bottom half of the image disappears; when you cover the bottom half of the lens, the top half of the image disappears c) the image becomes half as bright in both cases d) nothing happens in either case e) the image disappears in both cases

c) The image is formed on the screen when light from all parts of the object passes through an entire lens. If half of the lens is covered that means only half of the light ray is used to produce the image and the image is still produced. When either top or bottom half of the lens is covered, half of the light rays are blocks, so that only half of the light ray reaches the image which results in low intensity image as compared with with a lens without a cover.

If you shine a light through an optical fiber, why does it come out the end but not out the sides? a) It does come out the sides, but this effect is not obvious because the sides are so much longer than the ends b) the sides are mirrored, so the light reflects c) Total internal reflection makes the light reflects from the sides d) the light flows along the length of the fiber, never touching the sides

c) When the light is passed through an optical fiber and the index of refraction of the air is less than the index of refraction of fiber the light inside the fiber will be totally reflected from the sides of the fiber. The sides of the optical fiber are perpendicular to the end, so the angle made by the light is less than the critical angle and the light exits.

When you look at a fish in a still stream from the bank, the fish appears shallower than it really is due to refraction. From directly above, it appears a)deeper than it really is b) at its actual depth c) shallower than its real depth d) It depends on your height above the water

c) When the light rays travel from lower refractive index medium to a higher refractive index medium, light is refracted and bends away from the normal. Due to this bending of light rays away from the normal, the fish appear to be a closer position. Thus the fish appear to be at a shallower position than its actual depth.

A lens can be characterized by its power, which a) is the same as the magnification b) tells how much light the lens can focus c) depends on where the object is located d) is the reciprocal of the focal length

d) The power of the lens is used to know the strength of the lens, which means how strongly the light gets converged or diverged when it is passing through the lens. Thus power is defined as the reciprocal of the focal length. Converging lens have positive optical power and diverging lens have negative power.

Which of the following can form an image? a) a plane mirror b) a curved mirror c) a lens curved on both sides d) a lens curved on only one side e) all of the above

e

A converging lens, such as a typical magnifying glass, a) always produces a magnified image (taller than the object) b) always produces an image smaller than the image c) always produces an upright image d) always produces an inverted image (upside down) e) none of these statements are true

e) The converging lens will act as a magnifier if the object is closer to the lens than the focal point. The type of image produced depends on how far the object is. The statement (a) that it will always produced the magnified image is wrong because when the object distance is greater than 2F, the focal image size will be reduced The statement b) that it will always produce an image smaller than the obejct is wrong because the if the object is placed between the focal length F and 2F, the image will be magnified The statement c) that it will always produce an upright image is wrong because it is only produced upright when the object is placed between the lens and the focal length The statement d) that it will produce an inverted image is wrong because when the object is placed at a distance greater than the focal length then only the inverted image is produced.

Parallel light rays cross interfaces from medium 1 into medium 2 and then into medium 3 as shown in fig. 23-51. What can we say about the relative sizes of the indices of refraction of these media? a)n1>n2>n3 b)n3>n2>n1 c) n2>n3>n1 d) n1>n3>n2 e) n2>n1>n3 f) none of the above

e) The light ray traveling from one medium to another medium will bend toward or away from the normal depending on upon the index of refraction of the two media Light ray traveling from medium 1 to medium 2 is bending toward the normal: n2>n1 When the light ray is traveling from medium 2 to medium 3, it is bending away from the normal that means the index of refraction of n2>n3 The angle in region 2 is greater than the angle in region 1, so n1>n3