# conceptual physics

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Chap. 29-31

A surface that is considered rough for infrared waves may be polished for

### away from normal

A beam of light emerges from water into air at an angle. The beam is bent

### the red glass

The average speed of light is greatest in

### below the sighted ﬁsh

If you wish to spear a ﬁsh with a regular spear, you should compensate for refraction between the air and water and throw your spear

### separate from one another

To say that energy levels in an atom are discrete is to say the energy levels are well deﬁned and

### only a photon of the same or lower energy

An atom that absorbs a photon of a certain energy can then emit

### all of these

Light from a laser is

### in the ground state

The fact that the air you breathe doesn't give oﬀ much visible light indicates that most of the electrons of its atoms are

### frequency

The energy of a photon depends on its

### the particle nature of light

The photoelectric eﬀect best demonstrates

### the number of electrons ejected per second

When a clean surface of potassium metal is exposed to blue light, electrons are emitted. If the intensity of the blue light is increased, which of the following will also increase?

### red

An excited atom decays to its ground state and emits a photon of green light. If instead the atom decays to an intermediate state, then the light emitted could be

### 6

A hypothetical atom has four distinct energy states. Assuming all transitions are possible, how many spectral lines can this atom produce?

### ultraviolet light.

Fluorescent brighteners (often called 'wave shifters') are added to laundry detergents to increase the amount of blue light emitted by aging, yellowed fabrics. Brighteners obtain the energy they need to emit this additional blue light from:

### blue light has a higher frequency than red light

Red light has a longer wavelength than blue light, so you know that, in empty space

### a.the bulb will emit a redder-than-normal light and will waste more energy producing infrared radiation.

A very-long-life incandescent light bulb insures that its filament will not sublime quickly by running the filament at a lower temperature than a normal bulb. Because of the low filament temperature

the bulb will emit bluer-than-normal light and will waste more

### normal bulb

the bulb will save energy by drawing less power from the power line while still producing the same amount of useful light as a

### than a normal bulb

the bulb will help save energy by drawing the same amount of power from the power line while producing more useful light

### Less bright and more red

During the summer, 'brownouts' (AC line voltage < 120V) are experienced in some large cities when the electrical demand exceeds supply. During a brownout, the light emitted from an incandescent lamp would be

### ultraviolet light

Electromagnetic radiation includes infrared, visible, and ultraviolet light. Although light travels as a wave, it is absorbed as individual particles called photons, which carry an amount of energy that depends on the frequency of the light. Of the three types of light mentioned above, the type of light that carries that most energy per photon is:

### a.travels the slowest in glass

When white light is separated into its colors by a glass prism, blue light is bent at the greatest angle. This means that, of all the colors, blue light

### their frequency.

The thing that is different between x-rays and radio waves is

### the speed at which they travel

and the thing that is the same of x-rays and radio waves is

### all of the time

An ice cube in a dark room emits electromagnetic ("black- body") radiation:

### an electron drops from a higher to a lower energy level

Emission of light from an atom occurs when?

### Bohr

Who is given credit for the uncertaintity principle?

### E = hv

Which of the following is Planck's equation?

### violet

Which of the following light waves has the greatest energy?

### the electron's main energy level

What does the first quantum number (n) stand for?

### an area where an electron has the greatest probability of being found

What is an electron cloud ?

### hc/E

Which of the following can be used to calculate the wavelength of a band of light?

### 3.00 X 10-8th

The speed of light in meters/sec. is

### line spectrum

Another name for atomic emission spectrum is

### wavelength

The frequency of a wave is inversely proportional to its

Microwaves have shorter wavelengths than

### None of these

Who proposed that light is emitted or absorbed by an object in fixed amounts called quanta?

### the energy of photons

Upon what does the photoelectric effect depend?

### light

What has properties of both particles and waves?

### line spectrum

What identifying feature of elements is produced when elements emit light?

### energy of electrons is quantized

Why do elements supposedly have unique line spectra?

### Heisenburg's Uncertainty Principle

When you measure the position of an electron, you invariably change the electron's momentum. This idea was stated in

### phase

A "wave front" is a surface of constant:

### both I and II

Consider (I) the law of reflection, and (II) the law of refraction. Huygens' principle can be used to derive:

### light is a wave phenomenon

Interference of light is evidence that:

### to create a path length difference

The reason there are two slits, rather than one, in a Young's experiment is:

### a wavelength

In a Young's double slit experiment, the center of a bright fringe occurs wherever waves from the slits differ in the distance they travel by a multiple of:

### two wavelengths

Waves from two slits are in phase at the slits and travel to a distant screen to produce the second side maximum of the interference pattern. The difference in the distance traveled by the waves is:

### use a blue filter instead of a yellow filter

Light from a small region of an ordinary incandescent bulb is passed through a yellow filter and then serves as the source for a Young's double slit experiment. Which of the following changes would cause the interference pattern to be more closely spaced?

### a halving of the fringe spacing

In a Young's double slit experiment, the slit separation is doubled. This results

### halve the slit separation

In an experiment to measure the wavelength of light using a double slit, it is found that the fringes are too close together to easily count them. To spread out the fringe pattern, one could:

### no phase change

Light in medium 1 of index of refraction n1 is reflected from an interface with medium 2 of index of refraction n2, where n1>n2. The reflected light gains:

### a phase change of π

Light in medium 1 of index of refraction n1 is reflected from an interface with medium 2 of index of refraction n2, where n1<n2. The reflected light gains:

### λ/4

Monochromatic light, at normal incidence, strikes a thin film in air. If λ denotes the wavelength in the film, what is the thinnest film in which the reflected light will be a maximum?

### the dark bands spread out, disappearing off the left edge

An air wedge is formed from two glass plates which are in contact at their left edges. There are ten dark bands when viewed by the reflection using monochromatic light. The left edge of the top plate is now slowly lifted until the plates are parallel. During this process:

### their phase difference is constant

If two light waves are coherent:

### the light must be coherent

To obtain an observable double-slit fringe pattern:

### diffraction

When a highly coherent beam of light is directed against a very fine wire, the shadow formed behind it is not just that of a single wire, but rather looks like the shadow of several parallel wires. The explanation of this involves:

### refraction

The rainbow seen after a rain shower is caused by:

### the midpoint of the slit

At the first minimum, adjacent to the central maximum of a single-slit diffraction pattern, the Huygens wavelet from the top of the slit is 180 degrees out of phase with the wavelet from:

### a point one-fourth of the slit width from the top

At the second minimum adjacent to the central maximum of a single-slit diffraction pattern, the Huygens wavelet from the top of the slit is 180 degrees out of phase with the wavelet from:

### none of the above

In a single-slit diffraction pattern, the central maximum is about twice as wide as the other maxima. This is because:

### the width of the central diffraction peak increases and the number of bright fringes within the peak stays the same

If we increase the wavelength of the light used to form a double-slit diffraction pattern:

### the intensity at the center of the pattern does not change and the pattern expands away from the bright center

A diffraction pattern is produced on a viewing screen by illuminating a long narrow slit with light of wavelength λ. If λ is increased and no other changes are made:

### increasing the lens diameters

The resolving power of a telescope can be increased by:

### become narrower

As more slits with the same spacing are added to a multiple-slit system, the lines:

### crowds together

A light spectrum is formed on a screen using a diffraction grating. The entire apparatus (source, grating, and screen) is now immersed in a liquid of index 1.33. As a result, the pattern on the screen:

### even order lines of the 450nm light coincide with lines of the 900nm light

A mixture of 450nm and 900nm light is incident on a multiple-slit system. Which of the following is true?

### form the arc of a half circle

At a diffraction line, phasors associated with waves from the slits of a multiple slit barrier:

### the orders of the lines that are missing are all multiples of 4

For a certain multiple-slit barrier, the slit separation is 4 times the slit width. For this system:

### the lines narrow

Two nearly equal wavelengths of light are incident on an N-slit grating. The two wavelengths are not resolvable. When N is increased they become resolvable. This is because:

### the slit separation should be decreased

To obtain greater dispersion by a multiple-slit system:

### 2

The frequency of light beam A is twice that of light beam B. The ratio EA/EB of photon energies is:

### greater for A than B

Light beams A and B have the same intensity but the wavelength associated with beam A is longer than that associated with beam B. The photon flux (number crossing a unit area per unit time) is:

### the number of photons that hit the sample

In a photoelectric effect experiment at a frequency above cut off, the number of electrons ejected is proportional to:

### none of the above

In Compton scattering from stationary electrons, the frequency of the emitted light is independent of:

### the photoelectric effect

Which of the following is NOT evidence for the wave nature of matter?

### the reflection of electrons by crystals

Of the following, which is the best evidence for the wave nature of matter? A. the photoelectric effect

### narrows

Monoenergetic electrons are incident on a single slit barrier. If the energy of each incident electron is increased, the central maximum of the diffraction pattern:

### has a longer wavelength and the same frequency

A free electron and a free proton have the same kinetic energy. This means that, compared to the matter wave associated with the proton, the matter wave associated with the electron:

### has the same wavelength and a greater frequency

A free electron and a free proton have the same momentum. This means that, compared to the matter wave associated with the proton, the matter wave associated with the electron:

### 3, 2, 1

Consider the following particles: 1. a free electron with kinetic energy K 2. a free proton with kinetic energy K 3. a free proton with kinetic energy 2K Rank them according to the wavelengths of their waves, least to greatest.

### the square of the magnitude of its wave function

The probability that a particle is in a given small region of space, is proportional to:

### probability density

The significance of |Ψ|2 is:

### the wave function is made less narrow

A free electron in motion along the x axis has a localized wave function. The uncertainty in its momentum is decreased if:

### none of the above

In order to tunnel through a potential barrier a particle must:

### L decreases without any other changes

An electron with energy E is incident on a potential energy barrier of height V and thickness L. The probability of tunneling increases if:

### ∫|ψ|2 dx = 1

If a wave function , ψ, for a particle moving along the x axis is 'normalized', then:

### n2

The energy of a particle in a one-dimensional trap with zero potential energy in the interior and infinite potential energy at the walls is proportional to (n = quantum number):

### 2, 3, 1

A particle is trapped in a one-dimensional well with infinite potential energy at the walls. Three possible pairs of energy levels are: 1. n=3 and n=1 2. n=3 and n=2 3. n=4 and n=3 Order these pairs according to the difference in energy, least to greatest:

### 2

Two one-dimensional traps have infinite potential at their walls. Trap A has width L and trap B has width 2L. For which value of the quantum number n does a particle in trap B have the same energy as a particle in the ground state of trap A?

### extends into the barriers

An electron is trapped in a one-dimensional well with finite potential energy barriers at the walls. The matter wave:

### 3

A particle is trapped in a finite potential energy well that is deep enough so that the electron can be in the state with n=4. For this state, how many nodes does the probability density have?

### hydrogen atom?

The quantum number n is most closely associated with what property of the electron in

### 13.6 eV

The binding energy of an electron, in the ground state, in a hydrogen atom is about:

### the circumference of each orbit is an integral multiple of electron wavelengths.

The main reason electrons occupy discrete orbits in an atom is because

### two thousand times the mass of an electron.

The mass of an atomic nucleon is nearly

### changes, but its mass number remains constant

When a nucleus emits a beta particle, its atomic number

### protons.

The atomic number of an element is the same as the number of its

### neutrons.

Diﬀerent isotopes of an element have diﬀerent numbers of

### 86

When radium (atomic number = 88) emits an alpha particle, the resulting nucleus has atomic number

### alpha particle

What experiences the greatest force in an electric field?

### 7.5 counts/min

A certain radioactive isotope placed near a Geiger counter registers 120 counts per minute. If the half life of the isotope is one day, what will the count rate be at the end of four days?

### frequency of 1000 Hz.

1.If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave having a

### green light

The worst thing you can do for the health of a green-leafed plant is to illuminate it with only

### perpendicular

Light will not pass through a pair of Polaroids when their axes are

### speed

Refraction results from differences in light's

### wavelength

When light is refracted, there is a change in its

### traveled slower in glass than it does.

Magnification from a lens would be greater if light

### the number of electrons ejected per second

When a clean surface of potassium metal is exposed to blue light, electrons are emitted. If the intensity of the blue light is increased, which of the following will also increase?

### a)Only a photon of the same or lower energy.

1.An atom that absorbs a photon of a certain energy can then emit

### violet

1.Which color of light carries the most energy per photon?

### All of these

The energy of a photon is related to

### a)Maximum velocity of ejected electrons.

1.In the photoelectric effect, the greater the frequency of the illuminating light, the greater the

### a)Less kinetic energy than the absorbed photon's energy.

1.In the photoelectric effect, electrons ejected from bound states in the photosensitive material have

### The electron

1.An electron and a baseball move at the same speed. Which has the longer wavelength?

### A low-energy electron

1.Which of the following has the longer wavelength?

### Number of ejected electrons.

1.In the photoelectric effect, the brighter the illuminating light on a photosensitive surface, the greater the

### red

1.An excited atom decays to its ground state and emits a photon of green light. If instead the atom decays to an intermediate state, then the light emitted could be

### De Broglie wavelengths.

1.In the Bohr model of hydrogen, discrete radii and energy states result when an electron circles the atom in an integral number of

### De Broglie wavelengths.

1.Orbital electrons do not spiral into the nucleus because of

### a)Radioactive decay in the Earth's core.

The source of the Earth's natural heat is

### All of these

1.The half-life of a radioactive substance is INDEPENDENT of

### Outer electrons.

1.Electrons with the greater potential energies with respect to the atomic nucleus are

### In the ground state.

1.The fact that the air you breathe doesn't give off much visible light indicates that most of the electrons of its atoms are

### Planck's constant

1.The ratio of a photon's energy to its frequency is

### a)The circumference of each orbit is an integral multiple of electron wavelengths.

1.The main reason electrons occupy discrete orbits in an atom is because

### None of these

1.When thorium (A = 90) emits a beta particle, the resulting nucleus has atomic number

### a)Ultraviolet photons kick atomic electrons in the mineral into higher energy states.

1.Some minerals glow when illuminated with ultraviolet light. This is because

### a)The potential difference required to stop them.

1.To study the energy of photoelectrons we measure

Example: