Test 3 Questions Flashcards
f
Positive:
Negative:
Positive: Concave Mirror
Negative: Convex/Diverging Mirror
do
Positive:
Negative:
Positive: Real Object
Negative: Virtual Object
di
Positive:
Negative:
Positive: Real Image
Negative: Virtual Image
m
Positive:
Negative:
Positive: Upright image
Negative: Inverted Image
All real images:
(a) are upright
(b) are inverted
(c) can appear on a screen
(d) cannot appear on a screen
(c) can appear on a screen
When an object is reflected in a plane mirror, the image is always
(a) real
(b) inverted
(c) enlarged
(d) left-right reversed
(d) left-right reversed
A dentist wants a small mirror that, when 2.20 cm from a tooth, will produce a 4.5 X upright image. What kind of mirror must be used and what must its radius of curvature be?
m=hi/ho=-di/do
4.5=-di/(2.20 cm), which gives di=-9.90 cm
The focal length is given by
1/do+1/di=1/f, i.e., 1/(2.20cm) +1/(-9.90 cm)=1/f, which yields f=2.83 cm
Focal length is positive, the mirror is concave with a radius of r=2f=5.7 cm
A light ray enters one medium from another along the normal. The angle of reflection
(a) is 0°
(b) is 90°
(c) equals the critical angle
(d) depends on the indexes of refraction of the two media.
(a) is 0°
When a beam of light enters one medium from another, a quantity that never changes is its
(a) direction
(b) speed
(c) frequency
(d) wavelength
(c) frequency
The index of refraction of a materials medium
(a) is always less than 1
(b) is always equal to 1
(c) is always equal to, or greater than 1
(d) may be less than, equal to, or greater than 1
(c) is always equal to, or greater than 1
A beam of parallel light enters a block of ice an angle of incidence of 30o. What is the angle refraction in the ice? (nair=1 and nice=1.31)
sinr=n1/ n2sini=1/1.31sin30o=0.382, thus, r=22o
When you look down into a swimming pool, are you likely to underestimate or overestimate its depth?
The pool appears shallower than it is.
A material has an index of refraction that increases continuously from top to bottom. Of the three paths shown in the figure below, which path will a light ray follow as it passes through the material?
When light goes from one material into one having a higher index of refraction, it refracts toward the normal line of the boundary between the two materials. If, as the light travels through the new material, the index of refraction continues to increase, the light ray will refract more and more
toward the normal line.!
As light travels from vacuum (n = 1) to a medium such as glass (n > 1), which of the following properties remains the same:
(a) wavelength
(b) wave speed
(c) frequency
(c). Both the wave speed and the wavelength decrease as the index of refraction increases. The frequency is
unchanged.
In a vacuum, the speed of an electromagnetic wave
(a) depends on its frequency
(b) depends on its wavelength
(c) depends on its electric and magnetic fields
(d) is a universal constant
(d) is a universal constant
Which one of the following statements concerning electromagnetic waves is false?
(a) Electromagnetic waves are longitudinal waves.
(b) Electromagnetic waves transfer energy through space.
(c) The existence of electromagnetic waves was predicted by Maxwell.
(d) Electromagnetic waves can propagate through a material substance.
(e) Electromagnetic waves do not require a physical medium
(a) Electromagnetic waves are longitudinal waves.
Which one of the following will not generate electromagnetic waves or pulses?
(a) a steady direct current
(b) an accelerating electron
(c) a proton in simple harmonic motion
(d) an alternating current
(e) charged particles traveling in a circular path in a mass spectrometer
(a) a steady direct current
Complete the following sentence: When electrons from a heated filament accelerate through vacuum toward a positive plate,
(a) only an electric field will be produced.
(b) only a magnetic field will be produced.
(c) electromagnetic waves will be produced.
(d) longitudinal waves will be produced.
(e) neither electric nor magnetic fields will be produced.
(c) electromagnetic waves will be produced.
Which one of the following types of wave is intrinsically different from the other four?
(a) radio waves
(b) gamma rays
(c) visible light
(d) sound waves
(e) ultraviolet radiation
(d) sound waves
Which one of the following statements concerning electromagnetic waves is false? (a) Electromagnetic waves carry energy.
(b) X-rays have longer wavelengths than radio waves.
(c) In vacuum, all electromagnetic waves travel at the same speed.
(d) Lower frequency electromagnetic waves can be produced by oscillating circuits.
(e) They consist of mutually perpendicular electric and magnetic fields that oscillate perpendicular to the direction of propagation.
(b) X-rays have longer wavelengths than radio waves.
Which one of the following statements concerning the wavelength of an electromagnetic wave in a vacuum is true?
(a) The wavelength is independent of the speed of the wave for a fixed frequency.
(b) The wavelength is inversely proportional to the speed of the wave.
(c) The wavelength is the same for all types of electromagnetic waves.
(d) The wavelength is directly proportional to the frequency of the wave.
(e) The wavelength is inversely proportional to the frequency of the wave.
(e) The wavelength is inversely proportional to the frequency of the wave.
Complete the following sentence: The various colors of visible light differ in
(a) frequency only.
(b) frequency and wavelength.
(c) wavelength only.
(d) frequency and their speed in a vacuum.
(e) their speeds in a vacuum.
(b) frequency and wavelength.
A cellular telephone transmits electromagnetic waves at a frequency of 935 MHz. What is the wavelength of these waves?
(a) 0.0106 m
(b) 0.321 m
(c) 0.642 m
(d) 1.22 m
(e) 2.40 m
(b) 0.321 m
An average distance between the surface of the earth and the surface of the sun is 1.49x1011 m. How much time, in minutes, does it take for light leaving the surface of the sun to reach the earth?
(a) zero minutes
(b) 2.9x10–3 min
(c) 8.3 min
(d) 74 min
(e) 500 min
(c) 8.3 min
Note the different types of electromagnetic radiation: (1) X-rays (2) radio waves (3) gamma rays (4) visible light (5) infrared radiation (6) ultraviolet radiation Which list correctly ranks the electromagnetic waves in order of increasing frequency? (a) 2, 3, 4, 5, 6, 1 (b) 2, 5, 4, 1, 6, 3 (c) 2, 5, 4, 6, 1, 3 (d) 3, 1, 6, 4, 5, 2 (e) 3, 6, 1, 4, 5, 2
(c) 2, 5, 4, 6, 1, 3
A plastic sandwich bag filled with water can act as a crude converging lens in air. If the bag is filled with air and placed under water, is the effective lens (a) converging or (b) diverging?
(b). In this case, the index of refraction of the lens material is less than that of the surrounding medium. Under these conditions, a biconvex lens will be
divergent.
An object is placed to the left of a converging lens. Which of the following statements are true and which are false?
(a) The image is always to the right of the lens.
(b) The image can be upright or inverted.
(c) The image is always smaller or the same size as the object.
(a) False. A virtual image is formed on the left side of the lens if do f.
(c) False. A magnified, real image is formed if 2f > do > f, and a magnified, virtual image is
formed if do > f.
An object infinitely far from a converging lens has an image that is
(a) real
(b) virtual
(c) upright
(d) larger than the object
(a) real
An object farther from a converging lens than its focal point always has an image that is
(a) inverted
(b) virtual
(c) the same in size
(d) smaller in size
(a) inverted
An object closer to a converging lens than its focal point always has an image that is
(a) inverted
(b) virtual
(c) the same in size
(d) smaller in size
(b) virtual
The image of a real object formed by a diverging lens is always
(a) real
(b) virtual
(c) inverted
(d) larger than the object
(b) virtual
Where must the film be placed If camera lens is to make a sharp image of an object very far away?
At the Focal Point
A converging lens may not have
(a) a positive focal length
(b) a negative focal length
(c) one plane surface
(d) one concave surface
(b) a negative focal length
A positive magnification signifies an image that is
(a) upright
(b) inverted
(c) smaller than the object
(d) larger than the object
(a) upright
A negative image distance signifies an image that is
(a) real
(b) virtual
(c) upright
(d) inverted
(b) virtual
A photographer moves closer to his subject and then refocuses. Does the camera lens move farther or near to the film?
Recall 1/f=1/do+1/di. In moving closer, do has decreased, so 1/do has increased. The equation requires that 1/di decreases so that the sum can remain the same. Therefore, di has increased, so the lens moves farther from the film.
(a) An object 31.5 cm in front of a certain lens is imaged 8.20 cm in front of that lens (on the same side as the object). What type of lens is this and what is its focal length? Is the image real or virtual?
(b) If the image were located, instead, 38.0 cm in front of the lens, what type of lens would it be and what focal length would it have?
(a) 1/do+1/di=1/f where do=31.5 cm, di=-8.20 cm 1/31.5+1/(-8.20)=1/f, which yields f=-11.1 cm, thus
diverging lens. The image is in front of the lens, so it is virtual
(b) Similarly, we have 1/31.5+1/(-38.0)=1/f. which gives f=+184 cm, thus, converging lens.
A cat stands facing a converging lens with its tail in the air. Under what circumstances would the image of the nose be virtual and the image of the tail be real? Where would be the image of the rest of the cat be?
if the object ( the nose) distance f, the lens produces a real image.
The image of the rest of the body (close to the focal point) would extend to infinity from either a real or virtual image.
In a double-slit experiment, the maximum intensity of the first bright line on either side of the central one occurs on the screen at locations where the arriving waves differs in path length by
(a) λ/4
(b) λ/2
(c) λ
(d) 2λ
(c) λ
Two rays of light from same sources destructively interfere if their path length differ by how much?
L2 - L1 = (m+1/2) λ
In a double-slit experiment it is found that blue light of wavelength 460 nm gives a second-order maximum at a certain location on the screen. What wavelength of visible light would have a minimum at the same location?
-For constructive interference
d sinΘ=mλ=2x460nm=920nm
-For destructive interference of the other light, we have d sinΘ=(m’+1/2)λ
-When the two angle are equal, then 920nm=(m’+1/2)λ
λ=1.84x103 nm for m’=0 λ=613 nm for m’=1 λ=368 nm for m’=2
The only wavelength here that is visible is 613 nm
Visible light includes wavelengths from 4x10-7 m to 7x10-7m. Find the angular width of the first-order spectrum produced by a grating ruled with 800 lines/cm
The slit space d that corresponding to 800 line/cm is d=(10-2 m/cm)/(8x103 lines/cm)=1.25x10-6 m
Since m=1,
sinΘb=λb/d = 4x10-7m/1.25x10-6m = 0.32, Θb=19o
sinΘr=λr/d = 7x10-7m/1.25x10-6m = 0.56, Θr=34o
The total width of the spectrum is therefore 34o-19o=15o
A characteristic property of the spectra produced by a diffraction grating is
(a) the sharpness of the bright lines
(b) diffuseness of the bright lines
(c) absence of bright lines
(d) absence of dark lines
(a) the sharpness of the bright lines
The greater the number of lines that are ruled on a grating of given width,
(a) The shorter the wavelengths that can be diffracted
(b) The longer the wavelengths that can be diffracted
(c) The narrower the spectrum that is produced
(d) The broader the spectrum that is produced
(d) The broader the spectrum that is produced
White light strikes (a) a diffraction grating, and (b) a prism. A rainbow appears on a screen just below the direction of horizontal incident beam in each case. What is the color of the top of the rainbow in each case?
(a) Violet for diffraction grating (mλ=dsinΘ)
b) Red for prism (n1/n2 = λ2/λ1
When the Young’s double slit apparatus is in the water, the interference fringes are
(a) more closely spaced
(b) more widely spaced
(c) spaced the same as when the apparatus is in air
(d) no longer well-defined
(b) more widely spaced
The theory of relativity is in conflict with
(a) experiment
(b) Newtonian mechanics
(c) electromagnetic theroy
(d) ordinary mathematics
(b) Newtonian mechanics
According to the principle of relativity, the laws of physics are the same in all frames of reference
(a) at rest with respect to one another
(b) moving toward or away from one another
at constant velocity
(c) moving parallel to one another at constant velocity
(d) all of the above
(d) all of the above
A young-looking woman astronaut has just arrived home from a long trip. She rushes up to an old gray-haired man and refers him as her son. How might this be possible?
Time dilation: Her clock and biological processes run slowly during her trip since she is moving relative to his rest frame, thus, she returned aged less than he did.
If you were on a spaceship traveling at 0.5 c away from a star, at what speed would the starlight pass you?
The speed of light in vacuum is the same by all observers (2nd Principle). You would find that the starlight passes you at c = 3x10^8 m/s
Find the speed relative to the earth of a spacecraft whose clock runs 1 s slow per day compared to a terrestrial clock.
t=24hx60mim/hx60s/min=86,400 s T=86,401 s
T = t/[1 - (v/c)2]1/2 or
v=c [1 - (t/T)2]1/2 =
=3x108 m/s (1-(86,400 s/86,401 s)2) =1.44x106 m/s
If you were traveling away from Earth at speed 0.5 c, would you notice a change in your heartbeat? Would your height and waistline change? What would observers on Earth using telescope say about you?
Since laws of physics are the same for all inertial observers, you would not notice any changes. However, observers on Earth watching you would say your heartbeat is slower, and you are thinner or shorter depending on which dimension of body is in the direction of motion.
Suppose the speed of light were infinite. What would you happen to the relativistic predications of length contraction and time dilation?
We would not have to take into account the time light takes to reach us, so none of the relativistic effects would apply, i.e., the relativistic factor (1-(v/c)2)-1/2 would be equal to 1.
A spacecraft has left the earth and is moving toward Mars. An observer on the earth finds that, relative to measurements made when it was at rest, the spacecraft’s
(a) length is greater
(b) mass is smaller
(c) clocks tick faster
(d) none of the above
(d) none of the above
If white light is used to illuminate an object that absorbs all color other than red, the object will appear red. What color will the object show if green light is used instead?
A white object reflects light of all wavelengths equally well, a black object, on the other hand, absorbs light of all wavelengths, and it appears black no matter what color light reaches it.
The color of an object we see depends on two things:
- The kind of light falling on it
2. Nature of its surface
The angle of incidence =
The angle of reflection
As light travels from one
medium to another…
Its frequency does not change.
– Both the wave speed and the wavelength do change.
– The wavefronts do not pile up, nor are they
created or destroyed at the boundary, so ƒ must stay the same.
Diffraction phenomenon significantly
depends on…
The ratio of the wavelength of
the wave to the size of the obstacle
We can hear sounds around the corners,
but we cannot see around corners; yet both sound and light are waves. Why?
Hearing sound around corners depends on
diffraction. The wavelengths of sound waves are comparable to the size of obstacles, and thus can diffract around obstacles, which block light waves.
Constructive Interference =
A1 + A2
In phase
Destructive Interference =
A1 - A2
Out of phase
We can easily observe interference in water waves, and hear beats, a result of interference in sound waves. But if we shine light from two flashlights on a screen, there is no evidence of interference. Why?
- Light waves have extremely short wavelengths (400nm-750nm)
- Natural light is incoherent (the phase relationship varies)
The term coherence relates to
(a) the phase relationship between two waves.
(b) the amplitude of two waves.
(c) the polarization state of two waves
(d) the frequency of two waves.
(e) the diffraction of two waves.
The phase relationship between two waves
Which one of the following statements best explains why interference patterns
are not usually observed for light from two ordinary light bulbs?
(a) Diffraction effects predominate.
(b) The two sources are out of phase.
(c) The two sources are not coherent.
(d) The interference pattern is too small to observe.
(e) Light from ordinary light bulbs is not polarized.
The two sources are not coherent.
For two light beams to interfere, their sources must be (a) coherent (b) incoherent (c) lasers (d) slits
Coherent
An interference pattern is produced whenever (a) reflection occurs (b) refraction occurs (c) diffraction occurs (d) polarization occurs
Diffraction occurs
Which one of the following phenomena would be observed if the wavelength of
light were increased?
(a) The fringes would be brighter.
(b) More bright fringes would appear on the screen.
(c) The distance between dark fringes would decrease.
(d) Single-slit diffraction effects would become non-negligible.
(e) The angular separation between bright fringes would increase.
The angular separation between bright fringes would increase.
Which one of the following phenomena would be observed if the distance between the slits were increased?
(a) The fringes would become brighter.
(b) The central bright fringe would change position.
(c) The distance between dark fringes would increase.
(d) The distance between bright fringes would increase.
(e) The angular separation between the dark fringes would decrease
The angular separation between the dark fringes would decrease
Which one of the following statements provides the most convincing evidence that
visible light is a form of electromagnetic radiation?
(a) Two light sources can be coherent.
(b) Light can be reflected from a surface.
(c) Light can be diffracted through an aperture.
(d) Light can form a double-slit interference pattern.
(e) Light travels through vacuum at the same speed as X-rays.
Light can form a double-slit interference pattern.
A changing magnetic field produces a changing electric field.
Faraday’s law
A changing electric field produces a changing magnetic field.
Maxwell’s hypothesis
Since all the colors have different angles of deviation, they will spread out into a spectrum – Which color deviates the most ? – Which color deviates the least ?
Violet deviates the most.
Red deviates the least.
What can occur when light attempts
to move from a medium with a high
index of refraction to one with a lower
index of refraction?
Total internal reflection
A converging lens brings _____ rays to a _____ focal point.
Parallel rays
Real focal point
The distance of the
focal point from the
center of the lens is
called the…
Focal length, f
A diverging lens spreads out _____ as though they came from a _____
focal point
Parallel rays
Virtual focal point
There are two difficulties in using a double
slit for measuring wavelengths. What are they?
1. The bright lines on the screen are actually extremely faint and an intense light source is therefore required; 2. The lines are relatively broad and it is hard to locate their center accurately.
A diffraction grating uses _____ to disperse light.
interference
Why do we say that light has wave properties? Why do we say that light has particle properties?
Experiments can provide evidence for both properties.
Name physical phenomenon as evidence for wave and particle properties, respectively.
Evidence for wave: interference, refraction, polarization
Evidence for particle: photoelectric effect, compton effect
Photoelectrons are emitted by a metal surface only when the light directed at it exceeds a certain minimum…
Frequency
When light is directed on a metal surface, the energies of the emitted electrons…
Vary with the frequency of light
Modern physical theories indicate that…
Only moving particles exhibit wave behavior
Observers moving relative to each other:
- Do not measure the same times.
- Disagree on what events occur simultaneously.
- Do not measure the same lengths of objects.
- Do not measure the same masses for objects
Mass and Energy are _____: E=mc2
equivalent
Massless particles must move at _____.
speed = c
Two observers moving relative to each other
experience the world differently:
• Both measure the same speed of light
• Both find the same physical laws relating
distance, time, mass, etc.
• But, both measure different distances,
times, masses, etc. applying those laws.
All uniformly moving observers see the same
_____.
All observers measure the same _____
physical laws
speed of light
