### GCSE Physics Revision: Soundwaves

#### 5th April 2017

GCSE Science - Physics – Sound and Sound Waves

KEY STAGE 4 – GCSE Physics Revision Guide

Then use this Revision Guide to remember all the Key Study Points and get Full Marks in your GCSE Physics Exam.

What is “Sound”?

When something (like a speaker) vibrates, it produces sound waves.

• Sound waves are longitudinal waves produced by vibration

Note: Longitudinal waves vibrate in the same direction as they travel!

• Sound waves require a medium to pass through (they cannot travel through a vacuum)

• Sound waves can travel through solid, liquid or gas and do so at different rates:

• Solids (fastest)

• Liquids (middle)

• Gases (slowest)

• Sound waves can bounce off other objects and produce echoes

Why do we hear different volumes and tones of sound?

This depends on two things:

• the amplitude (loudness) of the sound waves, and

• the frequency  (pitch) of the sound waves

Remember:

• High-Amplitude = High-Volume

• High-Frequency=High-Pitch

Example:

Two sounds with the same frequency, but different amplitudes, will sound the same (pitch), but different volumes/loudness.

On the other hand:

Two sounds with the same amplitude, but different frequencies, will have different pitches, but will sound just as loud as each other.

How is Frequency measured?

The most common unit of measure for Frequency is the Hertz:

• Number of waves per second = Hertz

What range of frequencies can humans hear?

• From 20 Hertz to 20 Kilohertz

• Remember: 1 Kilohertz = 1,000 Hertz

Human audible frequency range (decreases with age):

20 HERTZ ——————————————————————————————————-20,000 HERTZ

Above 20,000 Hertz is the Ultrasonic range.

How fast is the “Speed of Sound”?

This depends on the medium that the sound waves are travelling through:

• AIR = Three hundred and forty metres per second (340 mps)

• WATER = Fifteen hundred and sixty metres per second (1560 mps)

• STEEL = Five thousand metres per second (5000 mps)

What is the Speed of Light?

Approximately 300 MILLION metres per second (300,000,000 mps)

That is why you can see a lightning flash/bolt and then hear the thunder afterwards.

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