Chapter 7: Light

Which of the following is the binary representation of the number 20?

10100

A hot object starts to glow red when the temperature reaches _____. An incandescent lightbulb glows yellow-white at a temperature of about _____.

700 degrees C (1,300 degrees F); 2,200 degrees C (4,000 degrees F)

Planck's constant

A conversion to relate the frequency of light to the amount of energy in a photon.

photon

A single quantum of energy in the form of light.

quantum

A tiny, finite, discrete amount.

radio station

A tower emits analog of digital signals in the form of radio waves.

Maxwell

Created electric and magnetic field theory that described light as waves of electric and magnetic fields.

Fresnel

Demonstrated that many of light's properties can be represented mathematically as waves, and measured the wavelengths of visible colors of light.

reflection

Depending on the angle of incidence, outgoing waves are aligned more or less horizontally with a surface.

Planck

Determined that the energy of light depends on frequency and only exists in discrete amounts.

USB cable

Electrons carry voltage through a metal wire.

Einstein

Explained the photoelectric effect in terms of photons.

Foucault

Explained the photoelectric effect in terms of photons.

particle model

Explains light as individual packets of energy.

electromagnetic wave model

Explains the generation of light at a source.

electromagnetic wave model

Light can pass through empty space.

The current understand of light is best summarized by what statement?

Light exhibits characteristics of waves and particles, and either model may be appropriate for a given situation.

transverse wave model

Light exhibits polarization.

wave model

Light shows diffraction and inference patterns.

particle model

Light travels in straight lines.

The vibration of a wave can be along the direction of travel of perpendicular to the direction of travel. ________ waves vibrate along the direction of motion. _______ waves vibrate at a right angle to the direction of motion.

Longitudinal; Transverse

selective absorption

Only the waves aligned with the preferred polarization of the material are able to pass, others are blocked.

representing light as a ray

Predict the angle of a reflection off a mirror.

high intensity, high frequency

Produces a large current of high-energy electrons.

high intensity, low frequency

Produces a large current of low-energy electrons.

low intensity, high frequency

Produces a small current of high-energy electrons.

low intensity, low frequency

Produces a small current of low-energy electrons.

Hyugens

Proposed that light was a longitudinal wave.

Newton

Proposed that light was tiny particles that travel at great speed.

optical fibers

Pulses of light travel through pure glass.

Young

Showed though experiment that light had wave properties such as interference.

scattering

Small particles absorb and reradiate light polarized with their directions of vibration.

Low-intensity and high-intensity light of the same wavelength is shone on the plate in the diagram. What results do you expect?

The low-intensity light produces a lower current (fewer electrons) but the same voltage (same energy).

intensity

The number of photons emitted by a light source.

frequency

The property that determines the energy of individual photons.

interference pattern

This describes a series of bright and dark spots or stripes resulting from the interaction of waves.

constructive interference

This is the addition of two aligned waves, resulting in a region brighter than either wave alone.

destructive interference

This is the cancellation of two waves that are misaligned, resulting in a region dimmer than either wave alone.

photon model

This is the photoelectric effect.

What statements are related to dispersing a spectrum?

a medium with an index of refraction that varies with wavelength; refraction of light; spatial separation of white light into its component colors

What are the steps to describe the encoding and transmission of a digital audio signal, such as over a fiber optics phone line?

a microphone picks up sound pressure waves from the air, which it converts to a fluctuating electrical signal; the strength of the electrical signal is measured at regular time intervals and the values recorded sequentially; the values are transmitted by ordered sequences of pulses of light; the pulses are used to construct electrical and then sound waves at the receiving end

White light is best described as ______.

a mixture of many colors

The light produced by incandescent light sources is generated by _____.

accelerating electric charges

opaque

an object that reflects and/or absorbs all the light that this it

transparent

an object that transmits light

What are places where light of the same wavelength from two sources would interfere constructively?

at a location where light from one source travels exactly two wavelengths farther than light from the other; at a location where the troughs of both waves arrive at the same time; at a location where the peaks of the two waves arrive simultaneously

What choices describe components of the global positioning system?

atomic clocks; 24 satellites; time-encoded radio signals

The information-carrying capacity of a transmission medium, such as a fiber optics cable, is its _______.

bandwidth

When light moves from a material with a higher speed of light into a material with a lower speed of light, the light ray ______.

bends toward the normal

Turning the light attached to a fiber optics system rapidly on and off is an easy way to transmit ______.

binary numbers; information using only one frequency of light; digital information

Plants and animals that produce their own light are said to be ______.

bioluminous

What are the colors of visible light from the highest frequency to the lowest frequency?

blue, green, yellow, red

What are the statements that describe laser light?

coherent; in phase (waves are aligned); single frequency

visible light is only part of the entire ______ spectrum.

electromagnetic

A galaxy is moving away from our home galaxy of the Milky Way at 35% the speed of light. if an astronomer measured the speed of light emitted by that galaxy, it would be _____.

equal to 3.00 x 10^8 m/s

special theory of relativity

explains how space and time are affected by motion

electromagnetic wave model

explains light, electricity, and magnetism

The sky appears blue because short wavelengths of light are scattered more strongly by the atmosphere than long wavelengths. What are the observations that are a result of the scattering?

fluorescent objects, which respond to ultraviolet light, appear to glow the most strongly at twilight; the sun is reddest at sunset; it is still light out for a while after the sun is below the horizon

The higher the _____ of alight source, the higher the energy of each individual photon emitted.

frequency

In Einstein's ______theory of relativity, gravity is understood to be the result of mass stretching the structure of four-dimensional spacetime.

general

reflection

happens when light bounces off a smooth surface

Filament lightbulbs, the wires in a toaster, and a fire are all examples of _____ light sources, which produce light over a wide range of wavelengths.

incandescent

The ratio of the speed of light in a vacuum to the speed of light in material is called the _____

index of refraction

We must model light as a wave or a particle depending on the situation because _____.

light is a small-scale phenomenon, and nature behaves differently on tiny scales

If you were designing a microscope or telescope, the _____ ______ model would be helpful for tracing light's path through the device.

light ray

A mirage of a lake in the desert, or of a car's reflection on hot rod, happens because _____.

light rays in hot air traveling parallel or toward the ground are bent upward at you when they encounter colder air higher up

What are statements that apply to real images?

light travels directly from the image to your eye; the image can be projected on a screen or recorded

What all occurs as the temperature of an object emitting blackbody radiation increases?

more light is produced; the peak of the emission shifts to bluer (shorter) wavelength

A radioactive particle moving at close to the speed of light takes longer to decay than a stationary sample in a lab. This is an example of the effect that ______ in the special theory of relativity.

moving clocks run more slowly

A concave mirror ______.

of the right curvature will create a real image; is bowl-shaped, with the inside lower than the edges; of the right curvature will create a magnified virtual image

What are the reasons that Newton supported a particle model of light?

particles would travel in a straight line because of his laws of motion; it made sense to him that particles would be created at a light source

The smallest single quantum (or packet) of energy produced by a source emitting blue light would be a blue ______.

photon

What are the two principles form which Einstein developed his special theory of relativity?

physical laws are the same in reference frames moving at constant velocity to each other; the speed of light is measured to be the same for all observers

Arrange the colors of visible light from the longest wavelength to the shortest.

red, orange, yellow, green, blue, violet

To measure the velocity of a car, you must find how fast it is moving compared to something else-for example, the road. In this example, the road defines a ______.

reference frame

The change in direction of a light ray when it passes from one substance into another is called _____.

refraction

general theory of relativity

relates gravity and the structure of space and time

Why does the sky appear blue?

short wavelengths of light are scattered more strongly than longer wavelengths

What are the steps that explain Newton's experiment with sunlight?

sunlight falls on a prism; the light is dispersed into a rainbow of colors; the light then falls on a second prism; the prism combines the rainbow into white light

A rainbow is made of arcs of color rather than straight lines because _____.

the arc of a given color defines a constant angle between you, the raindrops, and the Sun

What statements accurately summarize our present understanding of light?

the exact nature of light is not describable in terms of the everyday-sized world but can be approximated in different situations; light sometimes acts as a wave, and sometimes as a particle; the energy of light is divided into discrete packets called photons.

Sometimes two rainbows are visible, one outside the other. The colors of the outer rainbow are reversed because _____.

the light making up the second rainbow was reflected twice inside raindrops

Total internal reflection of a light ray means that _____.

the light ray does not escape the material; the angle of refraction is at least 90 degrees

The diagram shows light falling on a charged plate, causing a current. This demonstrates ______.

the photoelectric effect

The amount of refraction that occurs as light passes between two media depends on _____.

the ratio of the speed of light in the materials; the angle of incidence on the boundary; the ratio of the index of refraction of the materials

diffuse reaction

the result of light hitting a rough surface

Dispersion of light means _____.

the separation of light into different colors sorted by wavelength

What are statements that are true about the speed of light in transparent materials?

the speed is always less than the speed in a vacuum; the change in speed causes refraction when light enters a different material

What are true statements about observers and reference frames?

two objects that are moving at the same velocity compared to an observer could be in the same reference frame; an observer sees her own reference frame as stationary

A scientist might model light as electromagnetic waves to understand how an incandescent lightbulb work. She might model light as rays to _____.

understand the reflection from a glass window; design of optics of a microscope

The index of refraction of water is 1.33, and the index of refraction of glass is about 1.50. This means that light travels more quickly in_______.

water

The speed of light is equal to the product of the wave's _____ and _____.

wavelength; frequency