Physics Hughes Critical Thinking Guide

22. Does the Doppler effect occur for only some types of waves or all types of waves?

All waves. Sound, light, water... ALL!

26. Is interference a property of only some types of waves or of all types of waves?

All waves: light, sound, water.... ALL!

25. Distinguish between constructive interference and destructive interference.

Constructive- is the addition of two waves in phase (crest and crest) where the resulting wave amplitude is larger. Destructive- the addition of two waves which are out of phase ( crest and trough) , resulting in a smaller amplitude wave.

24. Would it be correct to say that the Doppler effect is the apparent change in the speed of a wave due to relative motion of the source?

NO. The Doppler Effect is the apparent change in frequency. (Medium determines speed!).

9. What is the period T of a pendulum that takes one second to make a complete back and forth vibration?

One second!

7. How far, in terms of wavelength, does a wave travel in one period?

One wavelength

12. New York's 300.0m high Citycorp tower oscillates in the wind with a period of 6.80s. What is the frequency?

T = 6.80 f is the reciprocal of that f=1/6.8s=0.147Hz

1. Distinguish among these different parts of a wave: amplitude, crest, trough, and wavelength.

The amplitude is the height of the wave (measured from the equilibrium to the crest), the crest is the highest point of the wave,the trough is the lowest point of the wave. The wavelength is the length of the wave, measured from crest to crest.

3. Does the medium in which a wave travels move along with the wave itself?

The medium does not travel with the wave, however it does oscillate with the wave.

2. Distinguish between the period and the frequency of a vibration or a wave. How do they relate to one another?

The period is the time between crests, the time it takes one wavelength to pass a point. The frequency is how many waves pass a point per unit time (second). They are inverses of each other.

15. If you triple the frequency of a vibrating object, what will happen to its period?

The period will become smaller, 1/3 to be exact.

4. How does the speed of a wave relate to its frequency and wavelength?

The speed is the wavelength times the frequency

8. What is the period of a pendulum?

The time it takes for the pendulum to make a complete back and forth vibration.

5. As the frequency of sound is increased, does the wavelength increase or decrease?

The wavelength decreases

6. Distinguish between a transverse wave and a longitudinal wave.

Transverse waves travel perpendicular to the direction of the wave Longitudinal waves travel parallel to the direction of the wave.

20. The lowest frequency we can hear is 20.0 Hz. Calculate the wavelength associated with this frequency for sound that travels at 340.0 m/s.

V = f 340 = 20 (divide both sides by 20) wavelength= 340m/s / 20Hz = 17m

18. Red light has a longer wavelength than violet light. Which has the greater frequency?

Violet light has a greater frequency (long wavelength means fewer waves per time)

32. A hiker shouts toward a vertical cliff 685 m away. The echo is heard 4.0 s later. (remember sound needed to go over and back for an echo... total distance is twice 685 m or 1370m.)

a. What is the speed of the sound wave? . (remember the sound needed to go over and back for an echo... total distance is twice 685 m or 1370m and you know the time it took) Velocity = d/t v=342.5m/s b. The wavelength of the sound is 0.75 m. What is its frequency? (Remember it is the same sound as in part a. You just found its speed...and its wavelength is given, use V = f ) f c. What is the period of the wave? T=0.0022s

31. A sound wave produced by a clock chime 515 m away is heard 1.5 s later.

a. What is the speed of the sound wave? (Hint: use velocity is distance over time) v=343.33m/s b. The sound wave has a frequency of 436 Hz. What is its period? T=0.0023s c. What is its wavelength? =0.79m

11. A nurse counts 76 heartbeats in one minute. What are the period and frequency of the heart?

f = cycles per second T = time for a cycle f=76/60=1.27Hz t=60/76 =0.79s

13. Calculate the speed of waves in a puddle that are 0. 15 m apart and made by tapping the water surface twice each second.

f=2Hz λ=0.15m v=0.3m/s waves that are 0. 15 m apart = wavelength tapping the water twice each second says f=2Hz

17.If a wave vibrates back-and-forth three times each second, and its wavelength is 2 meters, what is its frequency? Its period? Its speed?

f=3Hz ( three cycles each second), v= f = 3*2 = 6m/s T=0.333s

14.Calculate the speed of waves in water that are 0.4 m apart and have a frequency of 2 Hz.

v=0.8m/s

33. A sound wave with frequency of 262 Hz has a wavelength of 1.29 meters. What is the speed of the sound wave? (Use V = f )

v=262(1.29)=337.98m/s

16. While watching ocean waves at the dock of the bay, Otis notices that 10 waves pass beneath him in 30 seconds. He also notices that the crests of successive waves exactly coincide with the posts of the dock that are 5 meters apart. What are the period, frequency, wavelength, and speed of the ocean waves?

wavelength= 5m f=0.33Hz (think 10 waves in 30 seconds) T=3s V= 1.67m/s v = f

23. Astronomers find that light coming from point A at the edge of the sun has a slightly higher frequency than light from point B at the opposite edge. What do these measurements tell us about the sun's motion?

(Apparent higher frequency means "coming toward you". The sun is rotating from A toward B. (Doppler Effect makes frequency appear higher when object is coming toward us)

21. When a wave source moves toward a receiver, does the receiver encounter an increase in wave frequency, wave speed, or both?

(Moving wave source, think of Sheldon... Doppler effect!)Wave speed stays constant, only frequency will increase. (Doppler Effect doesn't change how fast the waves travel - the speed of the wave depends on the medium only.)

10. Suppose that a pendulum has a period of 1.5 seconds. How long does it take to make a complete back and forth vibration?

1.5 seconds IS GIVEN as the time for one complete a back and forth vibration.... So 1.5s IS the period! Is this 1.5 second period pendulum longer or shorter in length than a pendulum with a period of 1.0s? The 1.5s pendulum would be longer. ( longer string pendulums took more time to swing back and forth)