Echoes, loudness, pitch and ultrasound
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 1 worked example, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- A whale, a bat and a baby
- Echoes
- Using an echo
Read the transcript of the teaching part
Last time
Before we start: last time, in The electromagnetic spectrum, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
A whale, a bat and a baby
A bat finds an insect in the dark. A ship finds the sea bed. A doctor sees an unborn baby. All three use the same trick: send out a sound, and measure how long it takes to come back. It is also how you tell a deep note from a high one, and a loud one from a quiet one.
Echoes
An echo is sound that has been reflected from a surface, such as a cliff or a wall, and is heard after the original sound. Hard, smooth surfaces reflect sound well. Soft surfaces such as curtains absorb it. The law of reflection applies to sound too. The angle of incidence equals the angle of reflection.
Using an echo
The sound travels to the wall and back, so the distance travelled is twice the distance to the wall. If the sound takes a time t to return, the distance to the wall is the speed multiplied by the time, divided by two. Always remember the divide-by-two.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Ultrasound · Loudness, pitch and quality · Ultrasound and its uses.
Chapter 3.4: Sound
- Sound waves and the speed of sound 5 min
- Echoes, loudness, pitch and ultrasound 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.