3.3.1 - 3.3.4 - Sound Flashcards
Explain Practical measuring the speed of sound between 2 points?
The aim of this experiment is to measure the speed of sound in air between two points
Use the trundle wheel to measure a distance of 100 m between two people
One of the people should have two wooden blocks, which they will bang together above their head to generate sound waves
The second person should have a stopwatch which they start when they see the first person banging the blocks together and stop when they hear the sound
This should be repeated several times and an average taken for the time travelled by the sound waves
Repeat this experiment for various distances
Explain practical 2 measure the speed of sound with Oscilloscopes?
The aim of this experiment is to measure the speed of sound in air between two points using an oscilloscope
Connect two microphones to an oscilloscope
Place them about 2 m apart using a tape measure to measure the distance between them
Set up the oscilloscope so that it triggers when the first microphone detects a sound, and adjust the time base so that the sound arriving at both microphones can be seen on the screen
Make a large clap using the two wooden blocks next to the first microphone
Use the oscilloscope to determine the time at which the clap reaches each microphone and the time difference between them
What is the oscilloscope?
An oscilloscope is a device that can be used to study a rapidly changing signal, such as:
A sound wave
An alternating current
When a microphone is connected to an oscilloscope, the (longitudinal) sound wave is displayed as though it were a transverse wave on the screen
The time base (like the ‘x-axis’) is used to measure the time period of the wave
The height of the wave (measured from the centre of the screen) is related to the amplitude of the sound
The number of entire waves that appear on the screen is related to the frequency of the wave
If the frequency of the sound wave increases, more waves are displayed on screen
Explain Core Practical 7: Using an Oscilloscope
The aim of this experiment is to investigate the frequency of a sound wave using an oscilloscope
Connect the microphone to the oscilloscope as shown in the image above
Test the microphone displays a signal by humming
Adjust the time base of the oscilloscope until the signal fits on the screen - ensure that multiple complete waves can be seen
Strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
Hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
Freeze the image on the oscilloscope screen, or take a picture of it
Measure and record the time period of the wave signal on the screen by counting the number of divisions for one complete wave cycle
Repeat steps 4-6 for a variety of tuning forks
What are the analysis of this result?
To convert the time period of the wave from the number of divisions into seconds, use the scale of the time base. For example:
The time base is usually measured in units of ms/cm (milliseconds per centimetre)
This would mean a wave with a time base of 4 cm has a time period of 4 ms
To calculate the frequency of the sound waves produced by the tuning forks, use the equation:
What is pitch?
The pitch of a sound is related to the frequency of the vibrating source of sound waves
If the frequency of vibration is high, the sound wave has a high pitch
If the frequency of vibration is low, the sound wave has a low pitch
What is Loudness
The loudness of a sound is related to the amplitude of the vibrating source of sound waves
If the sound is loud, the sound wave has a large amplitude
What is the range of human hearing?
The human ear responds to the vibrations caused by sound waves
The frequency range for human hearing is 20 Hz to 20 000 Hz
