Chapter Questions
Newton believed that light beams consist of tiny particles. If these beams travel in straight lines, what does that imply about their speed?
How does the particle theory of light account for the diffuse reflection of light?
Argue that the law of reflection would not hold for particles rebounding from a surface that is not frictionless or not perfectly elastic.
When a particle reflects elastically from a smooth surface, the component of the particle's momentum parallel to the surface is conserved while the component of the particle's momentum perpendicular to the surface is reversed. Use this information to argue that Newton's particle theory of light is consistent with the observation that the angle of incidence equals the angle of reflection.
If particles incident at 45 degrees from the normal strike a completely elastic surface that has friction, will the angle of reflection (with respect to the normal) be greater than, equal to, or less than 45 degrees? Explain.
If particles incident at 45 degrees from the normal strike a frictionless surface that is not completely elastic, will the angle of reflection (with respect to the normal) be greater than, equal to, or less than 45 degrees? Explain.
How does Newton's idea of light particles explain the law of refraction?
Explain how Newton's idea of light particles predicts that the speed of light in a transparent material will be faster than in a vacuum.
Does the wave's frequency or its wavelength remain the same when the wave crosses from one medium into another? Explain.
In which region of Figure $19-3$ (a) (top left or bottom right) are the waves traveling at the higher speed? Explain.
Which color of light, red or blue, travels faster in a diamond? Explain your reasoning.
Do you expect the speed of light in glass to be slower than, faster than, or the same as that in diamond? Why?
What property of a light wave determines its brightness?
Does the amplitude of a light wave increase, decrease, or stay the same on reflection from a transparent material? Explain.
Starting with the observation that waves that have been bent toward the normal have a shorter wavelength than the incident waves, explain how the wave model for light predicts that the speed of light in glass will be slower than the speed in a vacuum.
Imagine that Newton knew that light travels slower in glass than in air but was unaware of the law of refraction. In what direction would he have predicted light to bend when passing from air into glass?
Does total internal reflection result from light trying to pass from a slow medium to a fast medium or from a fast medium to a slow medium? Explain.
Different colors of light have different critical angles for total internal reflection. Is the critical angle greater for colors of light that travel faster or slower in the medium? Explain.
What is the physical difference between red and blue light?
How does the slow speed of light in diamonds affect their brilliance?
Why do we not notice any dispersion when white light passes through a windowpane?
What does the dispersion of light tell us about the speeds of various colors of light in a material?
Will the converging lens in the following figure focus blue light or red light at a closer distance to the lens? Explain.
Using blue light, you determine the focal point for the lens in the preceding figure. If you were to shine a green laser beam from this focal point to a point near the top of the lens, would the emerging beam be bent toward or away from the optic axis? Explain.
Red light is used to form a two-slit interference pattern on a screen. As the two slits are moved farther apart, does the separation of the bright bands on the screen decrease, increase, or remain the same? Why?
What happens to the separation of the bright bands in a two-slit interference pattern if the slits are made narrower but their separation remains the same?
Would yellow light or green light produce the wider two slit interference pattern? Why?
We observe that the two-slit interference pattern produced by blue light is narrower than that produced by red light. What does this tell us about red and blue light?
What determines whether two light beams with the same wavelength tend to cancel or reinforce each other?
Why don't we notice interference patterns when we turn on two lights in a room?
If light and sound are both wave phenomena, why can we hear sounds around a corner but cannot see around a corner?
Approximately how narrow should a slit be for the diffraction of visible light to be observable?
Blue light is used to form a single-slit diffraction pattern on a screen. As the slit is made wider, does the separation of the bright bands on the screen decrease, increase, or remain the same? Explain.
Would orange light or blue light produce the wider diffraction pattern? Why?
Would a slit with a width of 300 nanometers or of 400 nanometers produce a wider diffraction pattern when illuminated by light of the same wavelength? Why?
Which of the following single-slit diffraction experiments would produce the wider diffraction pattern: 800 -nanometer light passing through a 500 -nanometer-wide slit, or 450 -nanometer light passing through a 400 -nanometerwide slit? Why?
Why can't an ordinary microscope using visible light be used to observe individual molecules?
A common technique used by astronomers for overcoming diffraction limits is to electronically combine the light from more than one telescope. This effectively increases the diameter of the aperture to the distance between the telescopes. If the signals from two 5 -meter-diameter telescopes located 100 meters apart were being combined when one of the telescopes stopped functioning, by what factor would the minimum resolvable angle be increased?(IMAGE CANNOT COPY)
Will you observe multicolored patterns if you illuminate a thin soap film with monochromatic light? Why?
A thin film of oil on top of a bucket of water produces multicolored patterns. However, a bucket full of oil produces no such effect. Explain the difference.
Assume that you have the thinnest film that strongly reflects red light. Would you need to make the film thinner or thicker to completely reflect blue light? Why?
You are coating glass with a film of higher index of refraction. You make the thinnest film that will produce a strong reflection for a particular monochromatic light source. You then gradually increase the film's thickness until you find another strong reflection. How many times thicker is this film than the original?
A glass pane with index of refraction 1.5 is coated with a thin film of a material with index of refraction 1.6 The coating is as thin as possible to produce maximum reflection for blue light. If this same material is used to coat a different kind of glass with index of refraction 1.9 the light reflected from the back surface of the film now experiences an inversion. Does the coating have to be thicker or thinner in this case to produce strong reflection? Explain.
The office workers in a skyscraper complain that the morning sun shines too brightly into their work areas. The problem is resolved by applying a thin film to each windowpane. The film has an index of refraction smaller than the glass and is designed to reflect yellow light when applied to the glass. If a sheet of this film is held in front of a yellow spotlight, would any of the light pass through the film? Explain.
A thin film in air strongly reflects orange light. Will it still reflect orange light when it is placed in water?
A thin, transparent film strongly reflects yellow light in air. What does the film do when it is applied to a glass lens that has a higher index of refraction than the film?
If all the labels had come off the sunglasses in the drug store, how could you tell which ones were polarized?
Can sound waves be polarized?
The digital displays at fuel pumps often use liquid crystal displays (LCDs) to show the price. Because the light from LCDs is polarized, they can often be impossible to read while wearing Polaroid sunglasses. What could you do to read the display without removing your glasses?
How could you use Polaroid sunglasses to tell whether light from the sky is polarized?
How would you distinguish a hologram from a flat transparency?
If each point on a holographic film contains the entire image, what is gained by making the hologram larger?
What kind of light is required to make a hologram of a three-dimensional object?
What kind of light is required to display a hologram?
To gather enough light to expose the film, long time exposures are often necessary to make holograms of inanimate objects. Why is a very powerful laser required to make a hologram of a person's face?
Which of the following phenomena does not show a difference between the wave theory and particle theory of light: reflection, refraction, interference, diffraction, or polarization?
What is the speed of light in glass with an index of refraction of $1.6 ?$
What is the speed of light in water?
The speed of light in diamond is $1.24 \times 10^{8} \mathrm{m} / \mathrm{s} .$ What is the index of refraction for diamond?
Zircon is sometimes used to make fake diamonds. What is its index of refraction if the speed of light in zircon is 1.6 $\times 10^{8} \mathrm{m} / \mathrm{s} ?$
If it takes light 5 ns ( 1 nanosecond $=10^{-9}$ s) to travel 1 m in an optical cable, what is the index of refraction of the cable?
If an optical cable has an index of refraction of $1.5,$ how long will it take a signal to travel between two points on opposite coasts of the United States separated by a distance of $5000 \mathrm{km} ?$
The index of refraction for red light in material $\mathrm{X}$ is measured at $1.80 .$ Blue light travels $5 \times 10^{6} \mathrm{m} / \mathrm{s}$ slower than red light in this material. What is the index of refraction for blue light in material $\mathrm{X} ?$
For crown glass, the index of refraction for violet light is 1.532 and the index of refraction for red light is 1.515 How much faster is red light than violet light in this medium?
What is the wavelength of the radio signal emitted by an AM station broadcasting at $1420 \mathrm{kHz}$ ? Radio waves travel at the speed of light.
What is the wavelength of light that has a frequency of 5 $\times 10^{14} \mathrm{Hz} ?$
The red light from a helium-neon laser has a wavelength of $633 \mathrm{nm} .$ What is its frequency?
What is the frequency of the yellow light with a wavelength of 590 nm that is emitted by sodium lamps?
What is the wavelength of the red light from a helium-neon laser when it is in glass with an index of refraction of $1.6 ?$ The wavelength in a vacuum is $633 \mathrm{nm}$
A transparent material is known to have an index of refraction equal to $1.9 .$ What is the wavelength of light in this material if it has a wavelength of $650 \mathrm{nm}$ in a vacuum?
Light from a sodium lamp with a wavelength in a vacuum of 590 nm enters diamond in which the speed of light is $1.24 \times 10^{8} \mathrm{m} / \mathrm{s} .$ What is the wavelength of this light in diamond?
What is the wavelength of light in water if it has a frequency of $6.6 \times 10^{14} \mathrm{Hz} ?$
For distant objects, the angular size in degrees can be approximated as $57^{\circ} \times w / d$, where $w$ is the width of the object and $d$ is its distance. What is the angular separation of the headlights on a car $10 \mathrm{km}$ away if the headlights are $1.2 \mathrm{m}$ apart?
The minimum angular separation in arc seconds $\left(\frac{1}{3600} \text { degree }\right)$ is found by first finding the ratio of the wavelength of light to the diameter of the aperture and then multiplying by $2.5 \times 10^{5} .$ Using visible light with a wavelength of 550 nm, calculate the minimum angular separation for an eye with a pupil size of $5 \mathrm{mm}$.
Using the information in Exercise $74,$ find the theoretical resolution of a telescope with a 10 -m-diameter mirror for visible light at $550 \mathrm{nm}$
What is the theoretical resolution of a radio telescope with a 10 -m-diameter collecting dish for radio waves with a wavelength of $21 \mathrm{cm} ?$ (See Exercise 74 .)(IMAGE CANNOT COPY)
What is the thinnest soap film that will strongly reflect light with a wavelength of 400 nm in the film?
What is the thinnest soap film that will strongly reflect red light from a helium-neon laser? The wavelength of this light is $633 \mathrm{nm}$ in air and $470 \mathrm{nm}$ in soapy water.
You are coating a glass lens of index of refraction 1.6 with a film of material of index of refraction $1.7 .$ You start with the thinnest film possible that creates a strong reflection for 500 -nm light. You gradually increase the film thickness until you again get strong reflection. What is the thickness of the film now?
Repeat Exercise 79 for a glass lens of index of refraction 1.8