Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
4.13P Recall that sound with frequencies greater than 20 000 hertz, Hz, is…
Full specification wording
Topic 4 – Waves: 4.13P Recall that sound with frequencies greater than 20 000 hertz, Hz, is known as ultrasound
Frequency is the number of complete waves passing a point each second, measured in hertz, Hz, where one hertz equals one wave per second.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 12 of 15
Study notes
From the checked teaching notes for this specification point.
The idea
Frequency is the number of complete waves passing a point each second, measured in hertz, Hz, where one hertz equals one wave per second. Human hearing covers a limited range, and sound above the top of that range is called ultrasound. The specification sets the boundary at frequencies greater than 20 000 Hz: a sound of 20 000 Hz sits at the boundary, and anything above it, such as 40 000 Hz, is ultrasound. A sound below that value, for example 500 Hz or 15 000 Hz, is audible sound rather than ultrasound. In a multiple-choice question, read the value and its unit carefully, compare it with 20 000 Hz, and choose the option that is strictly greater than 20 000 Hz. Remember that 20 kHz is the same as 20 000 Hz, so a value written in kilohertz must be converted before you compare it.
What earns the marks
- States that ultrasound is sound with a frequency greater than 20 000 Hz.
- Identifies hertz, Hz, as the unit of frequency, with 1 Hz equal to one wave per second.
- Selects a value strictly above 20 000 Hz, such as 40 000 Hz, as ultrasound.
- Rejects values at or below 20 000 Hz, such as 15 000 Hz, as not ultrasound.
- Converts a frequency given in kilohertz to hertz before comparing it with the 20 000 Hz boundary.
Common mistakes and how to put them right
Treats 20 000 Hz itself as ultrasound.
Put it right: State that ultrasound is strictly greater than 20 000 Hz.
Compares a value in kilohertz directly with 20 000 without converting.
Put it right: Convert 20 kHz to 20 000 Hz first.
Confuses frequency with loudness.
Put it right: State that ultrasound is defined by frequency, not by how loud the sound is.
Chooses a low-frequency option such as 500 Hz.
Put it right: State that this lies below the ultrasound boundary.
Exam tips
- Check the unit in each option and convert kilohertz to hertz before comparing with 20 000 Hz.
- Apply the boundary strictly: only values greater than 20 000 Hz count as ultrasound.
- Eliminate options that are clearly audible-range frequencies before choosing between the remainder.
Try the lesson
The start of the Topic 4 – Waves: 4.13P Recall that sound with frequencies greater than 20 000 hertz, Hz, is known as ultrasound lesson, made from checked teaching notes for this specification point.
Have a go first
A sound wave has a frequency of 30 000 Hz. What name is given to sound with a frequency this high?
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