FIG. 6-1 Nature of a water wave in deep water. Each water molecule performs a periodic motion in a small circle. Because successive molecules reach the tops of their circles at slightly later times, their combination appears as a series of crests and troughs moving along the surface of the water. There is no net transfer of water by the wave.

FIG. 6-2 Transverse and longitudinal waves. (a) Transverse waves travel along the rope in the direction of the black arrow. The individual particles of the rope move back and forth (color arrows) perpendicular to the direction of the waves. (b) In longitudinal waves, successive regions of compression and rarefaction move along the spring. The particles of the spring move back and forth parallel to the spring.

FIG. 6-3 Sound waves produced by a loudspeaker. Alternate regions of compression and rarefaction move outward from the vibrating cone of the loudspeaker.

FIG. 6-4 Decibel scale for sounds. Each 10-dB change corresponds to a 10-fold change in sound energy.

FIG. 6-5 A transverse wave moving in the x direction whose displacements are in the y direction. The wavelength is l and the amplitude is A.

FIG. 6-6 Wave speed equals frequency times wavelength.

FIG. 6-7 Waves whose speed is 8.5 m/s and whose wavelength is 50 m have a frequency of 0.17 Hz. This means that such waves pass an anchored boat once every 5.9 s.

FIG. 6-8 Refraction of water waves. Waves approaching shore obliquely are turned because they move more slowly in shallow water near shore.

FIG. 6-9 A wave in a stretched rope is reflected when it reaches a fixed end. The reflected wave is inverted.

FIG. 6-10 Reflection of water waves. Waves approaching an obstacle obliquely appear to reform and move away in a different direction.

FIG. 6-11 Standing waves in a stretched rope.

FIG. 6-12 A few of the possible standing waves in a stretched string, such as a violin string.

FIG. 6-13 Interference. (a) Waves started along stretched strings AC and BC will interfere at C. (b) Constructive interference. (c) Destructive interference. (d) A mixture of constructive and destructive interference.

FIG. 6-14 Diffraction causes waves to bend around the corner of an obstacle into the "shadow" region. The diffracted waves spread out as though they originated at the corner of the obstacle and are weaker than the direct waves. The waves shown here could be of any kind, for instance, water waves, sound waves, or light waves.

FIG. 6-15 The doppler effect. At (a) the police car is standing still, and sound waves from its siren reach you at their normal frequency. At (b) the car approaches you, moving a distance x between two successive waves. To you, the wavelength is shorter by x than before and the frequency higher. At (c) the car moves away from you, again moving a distance x between successive sound waves. Here you find that the wavelength is longer by x and the frequency lower.

FIG. 6-16 The waveforms of sounds can be analyzed electronically with the help of an oscilloscope, a device that displays electric signals on the screen of a tube like the picture tube of a television set. A microphone is used to convert sound waves into electric signals, and these in turn can be displayed on the oscilloscope screen. "Pure" tones, like those produced by a tuning fork, have simple waveforms like that of Fig. 6-5, while musical instruments and the human voice produce complex waveforms. Ordinary nonmusical noises consist of waves with complex and rapidly changing forms.

FIG. 6-17 A pair of metal rods connected to an electrical oscillator (source of alternating current) give rise to coupled electric and magnetic fields that constitute electromagnetic waves. The waves spread out from their source with the speed of light.

FIG. 6-18 The electric and magnetic fields in an electromagnetic wave vary together. The fields are perpendicular to each other and to the direction of the wave.

FIG. 6-19 (a) In amplitude modulation (AM), variations in the amplitude of a constant-frequency radio wave constitute the signal being sent out. (b) In frequency modulation (FM), variations in the frequency of a constant-amplitude wave constitute the signal.

FIG. 6-20 The ionosphere is a region in the upper atmosphere who ionized layers make possible long-range radio communication by their ability to reflect short-wavelength radio waves.

FIG. 6-22 Formation of an image in a mirror. The image appears to be behind the mirror because we instinctively respond to light as though it travels in straight lines.

FIG. 6-23 (a) Light that strikes an irregular surface is scattered randomly and cannot form an image. (b) Light that strikes a smooth, flat surface is reflected at an angle equal to the angle of incidence. Such a surface acts as a mirror.

FIG. 6-25 Light is refracted when it travels obliquely from one medium to another. Here the effect of refraction is to make the water appear shallower than it actually is.

FIG. 6-26 Light rays are bent toward the perpendicular when they enter an optically denser medium, away from the perpendicular when they enter an optically less dense medium. A ray moving along the perpendicular is not bent. The paths taken by light rays are always reversible.

FIG. 6-27 Total internal reflection occurs when the angle through which a light ray going from one medium to a less optically dense medium is refracted by more than 90° .

FIG. 6-28 All the light reaching an underwater observer from above the surface is concentrated in a cone 98° wide, so that the observer sees a circle of light at the surface when looking upward.

FIG. 6-29 Light can be "piped" from one place to another by means of internal reflections in a glass rod. Using a cluster of glass fibers permits an image to be carried in this way.

FIG. 6-30 (a) A converging lens brings parallel rays of light together to focal point F. (b) A diverging lens spreads out parallel rays of light so that they seem to originate at a focal point F. In both cases the distance between F and the lens is the focal length f of the lens.

FIG. 6-32The larger the f-number of a camera diaphragm, the smaller the opening. The sequence of values is such that each change of one f-number changes the amount of light reaching the film by a factor of 2.

FIG. 6-33 The human eye, shown larger than life size. In dim light the iris opens wide to let enough light enter through the pupil for good vision.

FIG. 6-34 Locating the blind spot.

FIG. 6-35 (a) A normal eye. (b) Farsightedness can be corrected with a converging lens. (c) Nearsightedness can be corrected with a diverging lens.

FIG. 6-36 How a cross is seen (a) by a normal eye and (b) by an astigmatic eye.

FIG. 6-37 A cylindrical lens can improve the image formed by an astigmatic eye.

FIG. 6-38 (a) A diamond cut in the "brilliant" style has 33 facets in its upper part and 25 in its lower part. The proportions of the facets are critical in giving the maximum of sparkle. (b) Dispersion gives a cut diamond its fire.

FIG. 6-39 Rainbows are created by the dispersion of sunlight by raindrops. Red light arrives at the eye of the observer from the upper drop shown here, violet light from the lower drop. Other raindrops yield the other colors and produce a continuous arc in the sky.

FIG. 6-40 A white surface reflects all light that falls on it. A green surface reflects only green light and absorbs the rest. A black surface absorbs all light that falls on it.

FIG. 6-41 (a) The preferential scattering of blue light in the atmosphere is responsible for the blue color of the sky. (b) The remaining direct sunlight is reddish, which is the reason for the red color of the sun at sunrise and sunset.

FIG. 6-42 (a) Destructive and (b) constructive interference in a thin film for light of a particular wavelength. When the film has the thickness in (a), it appears dark; when it has the thickness in (b), it appears bright. Light of other wavelengths undergoes destructive and constructive interference at different film thicknesses.

FIG. 6-43 A large lens or mirror is better able to resolve nearby objects than a small one.