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

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

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

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

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

8. Clap test at 100 m (example data)

   Clap	Level (dB)	Time to arrive (s)
   soft	60	0.29
   loud	90	0.29

9. 7.

   Noah says the table shows that louder sounds travel faster. Does it support the claim?

   • Yes: the loud clap is 1,000 times as intense, so it must be faster
   • No: the loud clap took longer, so loud sounds travel slower
   • No: both took 0.29 s over 100 m, so both traveled at the same speed, about 343 m/s
   • Yes: the loud clap is 30 dB higher than the soft one and still arrived in the same time
10. 8.

    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?

    • Disagree: its wavelength in tissue is 0.385 mm, which is still too coarse to show millimeter details
    • Disagree: its wavelength in tissue is 38.5 mm, far larger than 1 mm; scanners use several MHz
    • Agree: ultrasound has such a short wavelength that millimeter details are easy to see
    • Agree: 38.5 mm is smaller than 1 mm, so the details can be seen
11. 9.

    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 5.6 m
    • About 32 m
    • About 15 m
12. 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 660 Hz
    • About 880 Hz
    • About 622 Hz
    • About 466 Hz