1.
Light is emitted when
Correct Answer
A. Electron clouds of atoms are forced into oscillation.
Explanation
Light is emitted when the electron clouds of atoms are forced into oscillation. This is because when an atom absorbs energy, its electrons move to higher energy levels. When these electrons return to their original energy levels, they release the excess energy in the form of light. This process is known as electron transition or electron oscillation, and it is responsible for the emission of light. Atomic nuclei vibrating, electromagnetic waves emanating from matter, and high-frequency sound waves striking matter do not directly result in the emission of light.
2.
Light will almost always travel from one place to another along a path of least
Correct Answer
B. Time.
Explanation
Light will almost always travel from one place to another along a path of least time. This is because light travels at a constant speed in a vacuum, and it follows the principle of least time, which states that light will take the path that requires the least amount of time to reach its destination. This principle is based on Fermat's principle of least time, which states that light follows the path that minimizes the travel time between two points. Therefore, when light travels from one place to another, it will always take the path that minimizes the time taken.
3.
The incident light ray, the reflected light ray, and the normal between them
Correct Answer
A. Lie in the same plane.
Explanation
When light rays interact with a surface, the incident ray (the incoming ray), the reflected ray (the ray bouncing off the surface), and the normal (a line perpendicular to the surface) all lie in the same plane. This is known as the law of reflection. The incident ray and the reflected ray are on opposite sides of the normal, and they both lie in the same plane as the normal. Therefore, the correct answer is that they lie in the same plane.
4.
Object and image for a plane mirror lie
Correct Answer
B. Equal distances from the mirror.
Explanation
When an object is placed in front of a plane mirror, the image formed is a virtual image that appears to be behind the mirror. The image is formed by the reflection of light rays from the object. In a plane mirror, the reflection occurs at the same angle as the incidence, resulting in the image appearing to be the same distance behind the mirror as the object is in front of it. Therefore, the object and its image in a plane mirror lie at equal distances from the mirror.
5.
The amount of light reflected from the front surface of a common windowpane is about
Correct Answer
A. 4 percent.
Explanation
The correct answer is 4 percent because windowpanes are designed to allow light to pass through them rather than reflect it. Therefore, only a small amount of light is reflected from the front surface of a common windowpane, which is approximately 4 percent.
6.
Diffuse reflection occurs when the size of surface irregularities is
Correct Answer
B. Large compared to the wavelength of the light used.
Explanation
Diffuse reflection occurs when the size of surface irregularities is large compared to the wavelength of the light used. This means that the surface is rough and uneven, causing the light to scatter in different directions. In contrast, if the surface irregularities are small compared to the wavelength of light, the reflection would be specular, where the light reflects at the same angle as it hits the surface. Therefore, the correct answer is that diffuse reflection occurs when the size of surface irregularities is large compared to the wavelength of the light used.
7.
A surface that is considered rough for infrared waves may be polished for
Correct Answer
A. Radio waves.
Explanation
The answer is radio waves because different types of waves interact with surfaces differently. Infrared waves are sensitive to surface roughness and can be absorbed or scattered by rough surfaces, while radio waves are less affected by surface roughness and can pass through or bounce off smoothly. Therefore, a surface that is considered rough for infrared waves can be polished to improve the transmission or reflection of radio waves. Light waves, on the other hand, are also affected by surface roughness and polishing would improve their transmission as well.
8.
When light reflects from a surface, there is a change in its
Correct Answer
E. None of these
Explanation
When light reflects from a surface, there is no change in its frequency, wavelength, or speed. The frequency and wavelength of light remain the same before and after reflection. The speed of light also remains constant in a given medium. Therefore, the correct answer is "none of these."
9.
If you walk towards a mirror at a certain speed, the relative speed between you and your image is
Correct Answer
C. Twice your speed.
Explanation
When you walk towards a mirror, your image in the mirror also appears to be walking towards you. This is because the light rays from your body reflect off the mirror and reach your eyes, creating the illusion of an image. Since you are moving towards the mirror and your image is also moving towards you, the relative speed between you and your image is the sum of your individual speeds. Therefore, the relative speed between you and your image is twice your speed.
10.
The shortest plane mirror in which you can see your entire image is
Correct Answer
A. Half your height.
Explanation
The correct answer is half your height. This is because a plane mirror reflects light at the same angle it hits the mirror, creating a virtual image that appears behind the mirror. In order to see your entire image in the mirror, the mirror must be tall enough to reflect the top of your head to the bottom of your feet. Therefore, a mirror that is half your height will be sufficient to see your entire image.
11.
To see his full height, a boy that is 1 meter tall needs a mirror that is at least
Correct Answer
B. 0.50 m tall.
Explanation
A mirror needs to be at least half the height of the person using it in order for them to see their full height. Since the boy is 1 meter tall, the mirror needs to be at least 0.50 meters tall.
12.
You wish to photograph the image of your little sister, who is standing 2 meters from a plane mirror. Holding the camera beside her head, you should set the distance for
Correct Answer
D. 4 meters.
Explanation
When photographing an image in a plane mirror, the distance between the camera and the mirror should be equal to the distance between the mirror and the object being photographed. In this case, since the little sister is standing 2 meters from the mirror, the camera should be placed 2 meters on the other side of the mirror, resulting in a total distance of 4 meters.
13.
A diver shines light up to the surface of a smooth pond at a 10-degree angle to the normal. Some light passes into the air above, and the part that reflects back into the water makes an angle to the normal of
Correct Answer
B. 10 degrees.
Explanation
When light travels from a denser medium (water) to a less dense medium (air), it undergoes a change in direction called refraction. The angle of refraction is determined by Snell's law, which states that the ratio of the sines of the angles of incidence and refraction is equal to the ratio of the velocities of light in the two media. In this case, since the angle of incidence is 10 degrees, the angle of refraction will also be 10 degrees. This means that the light that reflects back into the water will make an angle of 10 degrees with the normal.
14.
A yellow-white candle flame reflected from a piece of red glass shows two images; one from each surface.
Correct Answer
B. One image is yellow-white and the other red.
Explanation
When a yellow-white candle flame is reflected from a piece of red glass, it creates two images. One image is yellow-white because it is the reflection of the original flame. The other image appears red because the red glass filters out all colors except for red, resulting in a red reflection. Therefore, one image is yellow-white and the other is red.
15.
When you look at yourself in a pocket mirror, and then hold the mirror farther away, you see
Correct Answer
C. The same amount of yourself.
Explanation
When you look at yourself in a pocket mirror and hold it farther away, the size of your reflection in the mirror remains the same. This is because the mirror reflects light in a way that preserves the proportions and size of the objects being reflected. Therefore, regardless of the distance between the mirror and your face, you will see the same amount of yourself in the mirror.
16.
It is difficult to see the roadway in front of you when you are driving on a rainy night mainly because
Correct Answer
D. The film of water on the roadway makes the road less diffuse.
Explanation
The correct answer is that the film of water on the roadway makes the road less diffuse. When it rains, water accumulates on the road surface, creating a thin film. This film of water reduces the diffuse reflection of light from the road, causing less light to scatter in different directions. As a result, the road appears less illuminated, making it difficult to see the roadway clearly while driving on a rainy night.
17.
Standing at the shore of a still lake, the reflected view of scenery on the far side of the lake is the view you would see if you were upside down with your eye in the line of sight
Correct Answer
C. Directly beneath you, as far below water level as you are above.
Explanation
When standing at the shore of a still lake, the reflected view of the scenery on the far side of the lake is the view you would see if you were directly beneath yourself, as far below water level as you are above. This is because the reflection in the water appears to be a mirror image of the surroundings, and if you were upside down with your eye in the line of sight where it already is, the reflection would match the actual view. Therefore, the correct answer is directly beneath you, as far below water level as you are above.
18.
When a mirror with a fixed beam on it is rotated through a certain angle, the reflected beam is rotated through an angle that is
Correct Answer
B. Twice as large.
Explanation
When a mirror with a fixed beam on it is rotated through a certain angle, the reflected beam is rotated through an angle that is twice as large. This is because the angle of incidence is equal to the angle of reflection, and when the mirror is rotated, the incident angle and the reflected angle both change by the same amount. Therefore, if the mirror is rotated through an angle x, the incident angle changes by x and the reflected angle changes by 2x, making it twice as large as the angle of rotation.
19.
The inversion of your image in a plane mirror is actually an inversion of
Correct Answer
C. Front-back.
Explanation
When an object is reflected in a plane mirror, the image appears to be flipped from front to back. This means that the left and right sides of the object are switched in the reflection. However, the up-down orientation remains the same. Therefore, the inversion in a plane mirror is only in the front-back direction.
20.
Reflected light from the moon in a lake often appears as a vertical column when the water is
Correct Answer
B. Slightly rough.
Explanation
When the water in a lake is perfectly still, the reflection of the moon appears as a mirror image, without any distortion. However, when the water is slightly rough, the surface of the lake creates small ripples or waves. These ripples cause the reflected light from the moon to scatter and create a vertical column of light. This phenomenon is known as "scintillation" and is commonly observed when the water is slightly rough.
21.
Ninety-five percent of light incident on a mirror is reflected. How much light is reflected when three of these mirrors are arranged so light reflects from one after the other?
Correct Answer
C. 86%
Explanation
When light reflects off a mirror, 95% of it is reflected. If three mirrors are arranged in a way that light reflects from one mirror to the next, the amount of light reflected decreases each time. To find the total amount of light reflected, we need to multiply the reflection percentages of each mirror. 95% * 95% * 95% = 86.3375%, which can be rounded to 86%. Therefore, 86% of light is reflected when three mirrors are arranged in this way.
22.
Two plane mirrors are at right angles to each other. A coin placed near the mirrors has at most
Correct Answer
B. 3 images.
Explanation
When a coin is placed near two plane mirrors at right angles to each other, it undergoes multiple reflections. The first reflection occurs on one mirror, producing one image. This image is then reflected off the second mirror, creating a second image. Finally, the second image is reflected off the first mirror again, resulting in a third image. Therefore, the coin placed near the mirrors has at most three images.
23.
As a light ray enters or exits a water-air interface at an angle of 15 degrees with the normal, it
Correct Answer
A. Always bends toward the normal.
Explanation
When a light ray enters or exits a water-air interface at an angle of 15 degrees with the normal, it always bends toward the normal. This phenomenon is known as refraction. Refraction occurs because light travels at different speeds in different mediums. In this case, light travels slower in water than in air, causing it to change direction and bend towards the normal. This bending of light is a result of the change in the speed and direction of the light wave as it passes from one medium to another.
24.
When light passes through an ordinary window pane, its angle of emergence is
Correct Answer
C. The same as its angle of incidence.
Explanation
When light passes through an ordinary window pane, its angle of emergence is the same as its angle of incidence. This is because the window pane is made of a transparent material with a uniform refractive index, which means that the speed of light remains constant as it passes through the pane. According to the law of refraction, the angle of incidence and the angle of emergence are equal when light passes through a medium with a uniform refractive index. Therefore, the correct answer is that the angle of emergence is the same as its angle of incidence.
25.
Light travels fastest in
Correct Answer
C. A vacuum.
Explanation
Light travels fastest in a vacuum because there are no particles to slow it down. In a vacuum, there is no air or any other medium to impede the speed of light, allowing it to travel at its maximum velocity. In contrast, in both warm and cool air, there are molecules present that can scatter and absorb light, causing it to slow down. Therefore, a vacuum provides the least resistance to the propagation of light, resulting in its fastest speed.
26.
Atmospheric refraction makes the daylight hours a bit
Correct Answer
A. Longer.
Explanation
Atmospheric refraction is the bending of light as it passes through the Earth's atmosphere. This bending causes the light to follow a curved path, which results in the apparent position of the Sun being slightly higher in the sky than its actual position. As a result, the daylight hours appear longer than they would be without atmospheric refraction.
27.
A mirage is a result of atmospheric
Correct Answer
B. Refraction.
Explanation
A mirage is a phenomenon that occurs due to the refraction of light. Refraction happens when light passes through different mediums with varying densities, causing the light rays to change direction. In the case of a mirage, the air near the ground is hotter than the air above it, creating a gradient in the refractive index. This causes the light rays to bend and create an optical illusion, making distant objects appear distorted or displaced. Therefore, the correct answer is refraction.
28.
The twinkling of the stars is a result of atmospheric
Correct Answer
B. Refraction.
Explanation
The twinkling of stars is caused by the phenomenon of refraction. When starlight passes through the Earth's atmosphere, it encounters different layers of air with varying densities. These variations in density cause the light to bend or refract, resulting in the twinkling effect that we observe from the ground. This refraction is responsible for the apparent fluctuation in the brightness of stars, giving them a twinkling appearance.
29.
Refraction results from differences in light's
Correct Answer
C. Speed.
Explanation
Refraction is the bending of light as it passes from one medium to another due to the change in its speed. When light travels from a medium with one speed to a medium with a different speed, it changes direction. This change in speed causes the light to bend, resulting in refraction. Therefore, the correct answer is speed.
30.
Light refracts when traveling from air into glass because light
Correct Answer
E. Travels slower in glass than in air.
Explanation
When light travels from air into glass, it slows down due to the difference in the refractive indices of the two mediums. This change in speed causes the light to bend or refract.
31.
At night an underwater scuba diver aims his flashlight beam toward the surface at an angle of 15 degrees with the normal. Upon emerging, the beam angle will be
Correct Answer
C. More than 15 degrees.
Explanation
When light passes from one medium to another, it changes its direction. This phenomenon is known as refraction. The angle of refraction depends on the angle of incidence and the refractive indices of the two mediums involved. In this case, when the scuba diver's flashlight beam emerges from the water to the air, it will bend away from the normal. Since the angle of incidence is 15 degrees, the angle of refraction will be greater than 15 degrees. Therefore, the correct answer is "more than 15 degrees."
32.
When a light beam emerges from water into air, the average light speed
Correct Answer
A. Increases.
Explanation
When a light beam emerges from water into air, the average light speed increases. This is because the speed of light is slower in water compared to air. When the light beam enters air from water, it transitions from a slower medium to a faster medium, causing an increase in its average speed.
33.
Refraction causes the bottom of a swimming pool to appear
Correct Answer
B. Closer to the surface than it actually is.
Explanation
When light travels from one medium to another, such as from air to water in a swimming pool, it undergoes refraction. Refraction occurs because light travels at different speeds in different mediums. In this case, as light enters the water, it slows down and bends towards the normal (an imaginary line perpendicular to the water's surface). This bending of light causes the bottom of the swimming pool to appear closer to the surface than it actually is.
34.
The average speed of light is greatest in
Correct Answer
A. Red glass.
Explanation
The average speed of light is greatest in red glass because red light has the longest wavelength among all visible colors. When light passes through a medium, its speed is inversely proportional to the refractive index of the medium. Since red light has a longer wavelength, it experiences less interaction with the atoms in the glass, resulting in a higher speed compared to other colors. Therefore, the average speed of light is greatest in red glass.
35.
Different colors are dispersed by a prism because different colors in the prism have different
Correct Answer
B. Speeds.
Explanation
Different colors are dispersed by a prism because different colors in the prism have different speeds. When white light passes through a prism, it is refracted at different angles depending on its wavelength. This causes the different colors of light to separate and form a spectrum. This phenomenon, known as dispersion, occurs because each color of light travels at a slightly different speed through the prism. Therefore, the correct answer is speeds.
36.
Rainbows are not usually seen as complete circles because
Correct Answer
A. The ground is usually in the way.
Explanation
Rainbows are not usually seen as complete circles because the ground is usually in the way. When we see a rainbow, it is formed by the reflection, refraction, and dispersion of sunlight in raindrops. The light enters the raindrop, reflects off the inside surface, and then exits the raindrop. However, to see a complete circle, the observer would need to be at a high vantage point, such as in an airplane or on a mountain, where the ground does not obstruct the view. Since most people view rainbows from ground level, the bottom half of the circle is blocked by the Earth's surface, resulting in an arched shape.
37.
A single raindrop illuminated by sunshine disperses
Correct Answer
B. Either low-, middle-, or high-frequency colors in most cases.
Explanation
When a raindrop is illuminated by sunshine, it acts as a prism and disperses the light into its constituent colors. This dispersion occurs because different colors of light have different frequencies. The low-frequency colors (such as red) are bent the least, while the high-frequency colors (such as violet) are bent the most. As a result, when we observe a raindrop, we see a range of colors, including low-, middle-, and high-frequency colors. Therefore, the correct answer is that a raindrop illuminated by sunshine disperses either low-, middle-, or high-frequency colors in most cases.
38.
When you view a distant rainbow, each single water drop contributes to the bow
Correct Answer
A. A single color.
Explanation
When viewing a distant rainbow, each single water drop contributes to the bow by refracting and dispersing light. This refraction and dispersion of light causes the different colors of the rainbow to separate and become visible. However, when we view the rainbow from a distance, we see a combination of all these colors blended together, appearing as a single color to our eyes. Therefore, when viewing a distant rainbow, each individual water drop contributes to the overall appearance of a single color.
39.
The secondary rainbow is dimmer than the primary rainbow because
Correct Answer
E. Of an extra reflection and refraction in the drops.
Explanation
The secondary rainbow is dimmer than the primary rainbow because of an extra reflection and refraction in the drops. When light enters a water droplet, it undergoes both reflection and refraction. In the case of the secondary rainbow, the light undergoes an additional reflection before exiting the droplet. This results in a more spread out and dispersed light, causing the secondary rainbow to appear dimmer compared to the primary rainbow.
40.
The critical angle for a transparent material is the angle at and beyond which all light within the material is
Correct Answer
B. Reflected.
Explanation
The critical angle for a transparent material is the angle at and beyond which all light within the material is reflected. This means that when light rays enter the material at an angle greater than the critical angle, they do not pass through the material but are instead reflected back.
41.
The critical angle is least in which of the following?
Correct Answer
C. Diamond
Explanation
The critical angle is the angle of incidence at which light is refracted along the boundary between two media. The critical angle is determined by the refractive indices of the two media involved. Diamond has a higher refractive index compared to glass, water, and vacuum. Since the critical angle is inversely proportional to the refractive index, diamond will have the least critical angle among the given options.
42.
In optical fibers of uniform density, light actually
Correct Answer
B. Travels in straight-line segments.
Explanation
In optical fibers of uniform density, light travels in straight-line segments. This is because the fiber is designed in such a way that the refractive index of the core is greater than the refractive index of the cladding. This causes the light to undergo total internal reflection, bouncing off the walls of the core and traveling in a straight path along the central axis of the fiber. This property allows for efficient transmission of light signals through the fiber without significant loss or distortion.
43.
Optical fibers are now used by
Correct Answer
D. All of these
Explanation
Optical fibers are now used by surgeons, mechanics, and engineers. Surgeons use optical fibers in minimally invasive surgeries to provide illumination and transmit images from inside the body. Mechanics use optical fibers for inspection and maintenance of hard-to-reach areas in machinery. Engineers utilize optical fibers for various applications such as telecommunications, data transmission, and sensing technology. Therefore, all of these professions benefit from the use of optical fibers.
44.
Your image in a plane mirror is
Correct Answer
D. Neither of these
Explanation
When you look at your image in a plane mirror, it is neither virtual nor real. A virtual image is formed when the light rays do not actually pass through the image, but appear to come from a different location. A real image is formed when the light rays actually converge at the location of the image. In the case of a plane mirror, the image formed is a reflection of the object, but the light rays do not converge or diverge, making the image neither virtual nor real.
45.
The type of lens that spreads parallel light is a
Correct Answer
B. Diverging lens.
Explanation
A diverging lens is the correct answer because it spreads parallel light rays outwards, causing them to diverge. This type of lens has a thinner center and thicker edges, causing light to refract away from the center. A converging lens, on the other hand, brings parallel light rays together at a focal point. A combination converging-diverging lens is not the correct answer as it would have both converging and diverging properties, which is not mentioned in the question.
46.
Which of the following can be projected onto a viewing screen?
Correct Answer
A. A real image
Explanation
A real image can be projected onto a viewing screen. A real image is formed when light rays actually converge at a point, creating an image that can be captured on a screen or a surface. This is in contrast to a virtual image, which is formed when light rays appear to diverge from a point, and cannot be projected onto a screen. Therefore, only a real image can be projected onto a viewing screen.
47.
A "burning glass" used to concentrate sunlight in a tiny spot is a
Correct Answer
A. Converging lens.
Explanation
A "burning glass" is a device used to concentrate sunlight in a tiny spot. This implies that the lens is able to converge the sunlight rays to a single point. Therefore, the correct answer is a converging lens, which has the ability to bring parallel rays of light together at a focal point.
48.
The image of the "infinitely-far-away" sun produced by a converging lens appears
Correct Answer
B. At the focal point.
Explanation
When an object is placed at an infinite distance from a converging lens, the lens forms an image at its focal point. This is because parallel rays of light from the object converge at the focal point after passing through the lens. Therefore, the image of the "infinitely-far-away" sun produced by a converging lens appears at the focal point.
49.
The image in a pinhole camera is
Correct Answer
A. Always inverted.
Explanation
The image in a pinhole camera is always inverted because the light rays passing through the small hole (pinhole) create an inverted image on the opposite side of the camera. This occurs because the rays diverge as they pass through the hole, resulting in an upside-down image. This phenomenon is a result of the basic principles of optics and the way light behaves when passing through a small aperture.
50.
When the pinhole in a pinhole camera is made larger, the image is
Correct Answer
A. Brighter.
Explanation
When the pinhole in a pinhole camera is made larger, more light is able to enter the camera. This results in a brighter image being formed on the camera's screen or film. By increasing the size of the pinhole, the camera is able to capture more light rays, allowing for a brighter and more illuminated image to be produced. Therefore, the image becomes brighter when the pinhole in a pinhole camera is made larger.