Sound: speed, pitch and loudness

Answer Key - Grade 11 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   A circle on a steel rail reaches the far end through steel (5940 m/s) and air (343.3 m/s), 0.274 s apart. How long is the rail, to the nearest meter, Ari?

   100 m
2. 2.

   A circle on a steel rail reaches the far end through steel (5940 m/s) and air (343.3 m/s), 0.549 s apart. How long is the rail, to the nearest meter, Bo?

   200 m
3. 3.

   A circle on a steel rail reaches the far end through steel (5940 m/s) and air (343.3 m/s), 1.372 s apart. How long is the rail, to the nearest meter, Esme?

   500 m

4. Read this first

   Speaker test (example data)

   Distance (m)	Level (dB)
   1	90
   2	84
   4	78
   8	72

5. 4.

   Which model fits the table, Jun?

   • Intensity stays the same with distance and just the pitch of the sound changes
   • Intensity falls in direct proportion to distance, so each doubling costs 3 dB
   • Intensity falls with the square of the distance, so each doubling costs 6 dB
   • The level falls by 6 dB for each extra meter, whatever the starting level is
6. 5.

   Using the same pattern, what level would the speaker give at 16 m, Kira?

   • 60 dB
   • 66 dB
   • 69 dB
   • 64 dB
7. 6.

   Milo says two 60 dB sounds played together make a 120 dB sound. Agree or disagree?

   • Disagree: the louder one hides the other, so the level stays at 60 dB
   • Disagree: two equal sources double the intensity, which adds about 3 dB, so about 63 dB
   • Disagree: the two sounds make 90 dB, since each adds half of its own level
   • Agree: levels in decibels add like ordinary numbers, so two 60 dB sounds make 120 dB in total
8. 7.

   Sound travels at about 1540 m/s in soft tissue. Pia says 40,000 Hz ultrasound could show 1 mm details in tissue. Agree or disagree?

   • Agree: ultrasound has such a short wavelength that millimeter details are easy to see
   • Disagree: its wavelength in tissue is 0.385 mm, which is still too coarse to show millimeter details
   • Agree: 38.5 mm is smaller than 1 mm, so the details can be seen
   • Disagree: its wavelength in tissue is 38.5 mm, far larger than 1 mm; scanners use several MHz
9. 8.

   A speaker gives 100 dBA at 1 m. How far from it must Ren stand for 85 dBA, the level safe for 8 hours?

   • About 2.8 m
   • About 32 m
   • About 15 m
   • About 5.6 m
10. 9.

    To find insects 3 mm wide, a bat's call needs a wavelength of 3 mm or less. Sound travels at 343.3 m/s in air. What frequency does Tala calculate it needs?

    • At least about 11,400 Hz
    • At least about 1,030 Hz
    • At least about 1,144,000 Hz
    • At least about 114,000 Hz
11. 10.

    A4 is 440 Hz. Each semitone multiplies the frequency by the same factor, and 12 semitones double it. What is the frequency 6 semitones above A4, Zee?

    • About 880 Hz
    • About 466 Hz
    • About 660 Hz
    • About 622 Hz