Pupil sheet · Echoes and ultrasound

Echoes and ultrasound — final check

Name ______________________ Date ____________

Work alone, with the lesson closed. Answer every question; there are no hints.

1. describe / calculate

A boat sounds its horn 765 m from a cliff, and the crew hears an echo. The speed of sound in air is 340 m/s. (a) Describe what the echo is. (b) Calculate how long after the horn sounds the crew hears the echo.

(b) Time to hear the echo: ______________ unit ________

(a) What the echo is

2. identify / calculate / explain

A pupil stands 60 m from a wall and times 30 intervals between claps four times: 10.62 s, 10.55 s, 11.40 s and 10.58 s. (a) Identify the anomalous time. (b) Calculate the speed of sound from the mean of the other three times. Give your answer to 2 significant figures. (c) Explain why 30 intervals are timed rather than one.

(a) Anomalous time: ______________ unit ________

(b) Speed of sound: ______________ unit ________

3. identify

Which of these frequencies is ultrasound?

Circle one answer.

0.025 MHz
200 Hz
19 000 Hz
2 kHz

4. calculate / explain

Supplement. A ship needs at least 15 m of water below its sonar to pass safely. Over a sandbank, the echo from the seabed returns 0.028 s after the pulse. Sound travels through the sea water at 1500 m/s. (a) Calculate the depth of water below the sonar. (b) Explain whether the ship can pass safely.

(a) Depth below the sonar: ______________ unit ________

(b) Can the ship pass safely?

5. describe / explain / suggest

Supplement. (a) Describe how ultrasound is used to check a steel rail for a crack inside it without damaging the rail. (b) Explain how the depth of a crack is found from the screen. (c) Suggest why a hospital uses ultrasound, not X-rays, to check the growth of an unborn baby every few weeks.

(a) How the rail is checked

(b) Finding the depth of a crack