91Ó°ÊÓ

If you place a perfectly clear piece of glass in perfectly clear water, you can still see the glass. Why?

When a wave source moves relative to the medium, a stationary observer measures changes in both wavelength and frequency. But when the observer moves and the source is stationary, only the frequency changes. Why the difference?

Why can a boat easily produce a shock wave on the water surface, while only a very high-speed aircraft can produce a sonic boom?

Ocean waves with 18-m wavelength travel at \(5.3 \mathrm{m} / \mathrm{s} .\) What's the time interval between wave crests passing a boat moored at a fixed location?

Ripples in a shallow puddle propagate at \(34 \mathrm{cm} / \mathrm{s}\). If the wave frequency is \(5.2 \mathrm{Hz}\), find (a) the period and (b) the wavelength.

An 89.5 -MHz FM radio wave propagates at the speed of light. What's its wavelength?

Calculate the wavelengths of (a) a 1.0 -MHz AM radio wave, (b) a channel 9 TV signal \((190 \mathrm{MHz}),\) (c) a police radar (10 GHz), (d) infrared radiation from a hot stove \(\left(4 \times 10^{13} \mathrm{Hz}\right)\) (e) green light \(\left(6.0 \times 10^{14} \mathrm{Hz}\right),\) and \((\mathrm{f}) 1.0 \times 10^{18}-\mathrm{Hz}\) X rays. All are electromagnetic waves that propagate at \(3.0 \times 10^{8} \mathrm{m} / \mathrm{s}.\)

Medical ultrasound waves travel at about \(1500 \mathrm{m} / \mathrm{s}\) in soft tissue. Higher frequencies provide clearer images but don't penetrate to deeper organs. Find the wavelengths of (a) 8.0 - MHz ultrasound used in fetal imaging and (b) \(3.5-\) MHz ultrasound used to image an adult's kidneys.

An ocean wave has period 4.1 s and wavelength 10.8 m. Find its (a) wave number and (b) angular frequency.

Find the (a) amplitude, (b) wavelength, (c) period, and (d) speed of a wave whose displacement is given by \(y=1.3 \cos (0.69 x+31 t),\) where \(x\) and \(y\) are in centimeters and t in seconds. (e) In which direction is the wave propagating?