# Unit 11 Extra Credit

Either print this page and complete or (better yet) neatly show your answers on a separate page of paper. All answers must be expressed as complete sentences and/or all work shown to receive credit

1. A common method of estimating how far a lightning flash is from you is to count the seconds between the flash and the thunder, and divide by three. The result is the distance in kilometers. Explain how this rule works.

2. A bat emits short pulses of high-frequency sound and detects the echoes.

a. In what way would the echoes from large and small insects compare if they were the same distance from the bat?

b. In what way would the echo from an insect flying toward the bat differ from that of an insect flying away from the bat?

3. Two flutes are tuning up. If the conductor hears that beat frequencyincreasing, are the two flute frequencies getting closer together or farther apart?

4. A rifle is fired in a valley with parallel vertical walls. The echo from one wall is heard 2.0 s after the rifle was fired. The echo from the other wall is heard 2.0 s after the first echo. How wide is the valley?

5. Carol drops a stone into a mine shaft 122.5 m deep. How soon after she drops the stone does she hear it hit the bottom of the shaft?

6. Ultrasound with a frequency of 4.25 MHz can be used to produce images of the human body. If the speed of sound in the body is the same as in salt waster, 1.50 km/s what is the wavelength in the body?

7. A slide whistle has a length of 27 cm. If you want to play a note one octave higher, the whistle should be how long?

8. A rock band plays at a 80-dB sound level. How many times greater is the sound pressure from another rock band playing at

a. 100 dB?

b. 120 dB?

9. If you hold a 1.0-m metal rod in the center and hit one end with a hammer, it will oscillate like an open pipe. Antinodes of air pressure corresponds to nodes of molecular motion, so there is a pressure antinode in the center of the bar. The speed of sound in aluminum is 5150 m/s. What would be the lowest frequency of oscillation?

10. During normal conversation, the amplitude of the pressure wave is 0.020 N/m2.

a. If the area of the eardrum is 0.52 cm2, what is the force on the eardrum?

b. The mechanical advantage of the bones in the inner ear is 1.5. What force is exerted on the oval window?

c. The area of the oval window is 0.026 cm2 . What is the pressure increase transmitted to the liquid in the cochlea?

11. One organ pipe has a length of 836 mm. A second pipe should have a pitch one major third higher. The pipe should be how long?

12. The Doppler shift was first tested in 1845 by the French scientist B. Ballot. He had a trumpet player sound an A, 440Hz, while riding on a flatcar pulled by a locomotive. At the same time, a stationary trumpeter played the same note. Ballot heard 3.0 beats per second. How fast was the train moving toward him?

#. Light takes 1.28 s to travel from the moon to Earth. What is the distance between them?

#. Suppose you wanted to measure the speed of light by putting a mirror on a distant mountain, setting off a camera flash, and measuring the time it takes the fln a light bulb in a parallel circuit burns out, how is the current affected?

13. How is the current in a series circuit affected when one or more electrical devices are added? Explain why.

14. How is the current in a parallel circuit affected when one or more electrical devices are added? Explain why.

15. In some of the older low-cost sets of Christmas-thould be used?

#. A streetlight contains two identical bulbs 3.3 m above the ground. If the community wants to save electrical energy by removing one bulb. how far from the ground should the streetlight be positioned to have the same illumination on the ground under the lamp?

#. A 10-cd point source lamp and a 60-cd point source lamp cast equal intensities on a wall. If the 10-cd lamp is 6.0 m from the wall, how far is the 60-cd lamp?

Resources for physics students are available through links on the GBS Physics Home Page. Such resources include the Multimedia Physics Studios (a collection of animations and movies which illustrate key physics concepts) and The Physics Classroom (an online tutorial written in an easy-to-understand language).