Physics 153 Exam 2

what is Fermat's principle of least time?

Light takes the quickest path in going from one place to another.

penumbra

a partial shadow

what kind of lens can be used to produce a real image? a virtual image?

a real image can only be made with a converging lens. a virtual image can be made with either a converging or diverging lens.

shadow

a region where light rays do not meet

what is the angle between a light ray and its wavefront?

a right angle

umbra

a total shadow

does a viewer see a single color or a spectrum of colors coming from a single faraway drop?

a viewer sees a single color from a single faraway drop

distinguish between a virtual image and a real image.

a virtual image, unlike a real image, cannot be displayed on a screen. A virtual image is upright, whereas a real image is inverted

materials generally become warmer when light is ___

absorbed by them

the blackness on the type on a page is due to ___

absorption

compared to the photon that enters a pane of window glass, that photon that emerges is___

an identical but different photon

when visible light is incident upon clear glass, atoms in the glass ___

are forced into vibration

if a nearsighted person wants thinner eyeglasses, is a higher or a lower index of refraction for the lenses recommended?

higher ~ a lens of higher index of refraction will allow thinner lenses.

how does the incident light that falls on an object affect the motion of electrons in the atom of an object?

incident light makes the electrons oscillate. the electrons then emit light or absorb light and convert it to heat

when a flashlight submerged in water shines up into the air above, does the speed of light increase or decrease when the light passes from water into the air?

increases

infrared waves are often called heat waves because they ___

induce resonance in molecules and increase internal energy in a substance

Real images are always ___

inverted with a converging lens

critical angle

is the minimum angle of incidence inside a medium at which a light ray is totally reflected

does a single raindrop illuminated by sunlight deflect light of a single color or does it disperse a spectrum of colors? does it do this by reflection, refraction, or both?

it disperses a spectrum of colors, by both reflection and refraction

how does refraction change the apparant depth of a swimming pool?

it makes the pool shallower - only 3/4s as deep

in which medium does light travel faster - thin air or dense air? how does this affect the length of daylight hours?

it travels faster in thin air, which makes sunlight curve and makes the days longer

compared to its average speed in air, the average speed of a beam of light in glass is __

less

the fact that you can see stars in the nighttime sky is evidence that

light can travel in a vacuum and our atmosphere is transparent to visible light

transparent

materials such as glass and water that allow light to pass through in straight lines

opaque

most things around us are ___, they absorb light without reemitting it

index of refraction, n

n = speed of light in vacuum / speed of light in material

materials that do not transmit visible light are said to be ___

opaque

which of these electromagnetic waves have the longest wavelength?

radio waves

is a mirage the outcome of refection or refraction? why does it happen?

refraction. light curves through warm, low-density air near the ground, where it travels faster

when ultraviolet light is incident upon glass, atoms in the glass __

resonate

dispersion

separation of light into colors arranged according to frequency

which of the following changes when light is refracted?

speed

law of reflection

the angle of incidence is equal to the angle of reflection

how does the average speed of light in glass compare to its speed in a vacuum?

the average speed of light in glass is about 67% of the speed of light in a vacuum

electromagnetic spectrum

the classification of electromagnetic waves according to frequency is the ___

total internal reflection

the complete reflection of light by the inside surface of a medium

what is the focal length of a lens? what is the focal point?

the distance between the center of the lens and either focal point is the focal length. the focal point is where all images are in focus

Fermat's principle of least time

the idea that light takes the quickest path in going from one place to another

relative to the distance of an object in front of a plane mirror, how far behind the mirror is the image?

the image is the same distance behind the plane mirror as the object is in front

what is the relationship between index of refraction and the speed of light in a material?

the index of refraction is inversely proportional to the speed of light in a material

when the wheel of a cart rolls from a smooth sidewalk onto a plot of grass, the interaction of the wheel with the blades of glass slows the wheel. what slows light when is passes from air into a glass of water?

the light oscillate electrons in the atoms of the glass of water. the electrons absorb some of the energy and reemit it after a delay at each atom

what is meant by critical angle?

the minimum angle of incidence inside a medium where light is totally reflected

where in the sky is the moon relative to the sun when the images are crescents?

the moon is in front of the sun and it covers only a part of the sun

lunar eclipse

the moon passes through the Earth's shadow

electromagnetic waves

the vibrating electric and magnetic fields regenerate each other to make up an __, which emanates (moves outward) from the vibrating charge.

why is a secondary rainbow dimmer than a primary bow? how are the colors arranged in the secondary bow?

there is a second reflection with a loss of light. the colors are in the opposite order of the primary bow, with red on the inside instead of the outside.

how does the frequency of reemitted light in a transparent material compare with the frequency of the light that stimulates its reemission?

they are the same

how does the speed of light that emerges from a pane of glass compare with the speed of light incident on the glass?

they are the same

what do electrons affected by illumination do when they are made to vibrate with great energy?

they reemit more light and collide with neighbors, thereby converting light energy to more internal energy

are eyeglasses made with "high index of refraction" materials thinner or thicker? why?

thinner. light bends more entering high index of refraction materials

light travels from one place to another in the least ___

time

light normally travels in straight lines, but it "bends" in optical fiber. explain.

total internal reflection keeps light trapped inside the optical fiber

in what region of the electromagnetic spectrum is the resonate frequency of electrons in glass?

ultraviolet

the natural frequency of the atoms in glass is in the

ultraviolet part of the spectrum

what is the fate of the energy in ultraviolet light that is incident upon glass?

ultraviolet will be absorbed by the resonate vibration of electrons and turned into eternal energy and a temperature increase

Virtual images are always ___

upright

which travels more slowly in glass, red light or ultraviolet light? why?

violet light travels slower because it is closer in frequency to the ultraviolet resonance of the atoms in the glass

glass is transparent to __

visible light

what is the fate of the energy in visible light that is incident upon glass?

visible light will be transmitted by the glass, losing little energy in the process, so the energy remains visible light energy

refraction

when light bends in passing obliquely from one medium to another

reflection

when light is returned into the medium from which it came ~ the process of ___

when is the angle at which a ray of light strikes glass not the same as the angle that exits?

when the glass strikes the glass in one medium (such as air) and exits the glass through another medium (such as water)

solar eclipse

when the shadow of the moon falls on earth

distinguish between a converging lens and a diverging lens

when two parallel rays of light pass through a converging lens, the rays bend towards each other. when they pass through a diverging lens, the rays move apart from each other.

can a surface be considered polished for some waves and not for others?

yes

does the law of reflection hold for curved mirrors?

yes, it is as if the curved mirror is made of many tiny plane mirrors as lightly different orientations to each other