Sound: speed, pitch and loudness

Answer Key - Grade 11 Science Worksheet

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

1. 1.

   A speaker measures 100 dB at 1 m. Sound spreads evenly, so intensity falls with the square of distance. What level is heard at 10 m, to the nearest dB, Ari?

   80 dB
2. 2.

   A speaker measures 94 dB at 2 m. Sound spreads evenly, so intensity falls with the square of distance. What level is heard at 20 m, to the nearest dB, Bo?

   74 dB
3. 3.

   A speaker measures 88 dB at 1 m. Sound spreads evenly, so intensity falls with the square of distance. What level is heard at 4 m, to the nearest dB, Esme?

   76 dB
4. 4.

   A sound's pressure amplitude doubles. Intensity goes with amplitude squared. By about how much does the level rise, Jun?

   • About 10 dB
   • About 3 dB
   • About 12 dB
   • About 6 dB
5. 5.

   A 70 dB sound and a 60 dB sound are played together. About what level results, Kira?

   • About 65 dB, the average of the two
   • About 70 dB, since the louder sound dominates
   • About 80 dB, since 70 + 10 is 80
   • About 130 dB, since the two levels add together

6. Read this first

   Sound levels (NIDCD)

   Sound	Level (dBA)
   normal conversation	60–70
   movie theater	74–104
   motorcycles and dirt bikes	80–110
   headphones at maximum volume	94–110
   fireworks show	140–160

7. 6.

   Using the table, how many times as intense is the top of the headphones range as the top of the conversation range, Luz?

   • 40 times
   • 1,000 times
   • 100,000 times
   • 10,000 times

8. Speed of sound in air (example data, rounded)

   Air temperature (°C)	Speed (m/s)
   0	331
   40	355

9. 7.

   Noah hears a clap's echo 0.50 s later on a 0 °C day and 0.50 s later on a 40 °C day. Which cliff is farther, and by how much?

   • The 40 °C cliff, by about 6 m
   • The 40 °C cliff, by about 12 m
   • The 0 °C cliff, by about 6 m
   • They are the same distance, since the delays are equal
10. 8.

    A guitar string vibrates at 220 Hz. Ren presses it at its midpoint, so half its length vibrates. What is the new frequency?

    • 220 Hz, since the tension is unchanged
    • 110 Hz
    • 440 Hz
    • 880 Hz
11. 9.

    A string vibrates at 220 Hz. Tala makes its tension 9 times as large. Wave speed goes with the square root of tension. What is the new frequency?

    • 660 Hz
    • 73 Hz
    • 1,980 Hz
    • 440 Hz
12. 10.

    Zee hears 3 beats each second between a 440 Hz fork and a guitar string. What could the string's frequency be?

    • Either 437 Hz or 443 Hz
    • 437 Hz, since the string must be lower than the fork
    • 443 Hz, since the string must be higher than the fork
    • 1,320 Hz, three times the fork's frequency