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Science
Exercise 5
- Sounds and Circuits
Sounds
All sounds begin with an object that is vibrating. These vibrations travel away
from the source. If these vibrations strike someone's eardrum, they may be
heard.
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Pitch and Frequency |
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Large objects vibrate slowly and produce only a few waves every second. These
waves tend to have a low frequency and produce low-pitched sounds. |
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Small objects vibrate quickly and produce lots of waves every second. These
waves tend to have a high frequency and produce high-pitched sounds. |
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The frequency of a wave is measured in hertz (Hz). An object which vibrates once
every second and produces one complete wave every second has a frequency of 1
Hz.
Loudness
Objects that vibrate with large amplitudes produce loud sounds. Objects that
have small vibrations produce quiet sounds.
Travelling Sound Waves
Sound waves travel by making particles vibrate. Sound can travel not just
through air, but through all solids, liquids and gases. However sound cannot
travel through a vacuum as there are no air particles present that can vibrate
and transmit the sound.
Echoes
When sound waves strike a hard surface they are reflected. This reflected sound
is called an echo. Ships use echoes to find the depth of the ocean beneath them.
An echo sounder emits sound waves down towards the seabed. When the sound waves
strike the seabed they are reflected back up towards the surface. A sound
detector on board the ship listens for the echo. The deeper the sea the longer
it takes for the echo to be heard.
Sound waves used in this way are called SONAR. This stands for Sound Navigation
And Ranging.
Sonar can also be used by fishing boats to locate shoals of fish. If an echo is
heard much sooner than expected this would suggest that fish were swimming
beneath the boat and the sound waves have reflected back off the shoal of fish.
Hearing Range
An average human being can hear sounds that have a frequency higher than 20 Hz
and lower than 20,000 Hz. This band of frequency is called our hearing range.
(It is also sometimes called our audible range). Hearing or audible ranges do
vary slightly from person to person. However our hearing range generally
narrows, as we grow older.
Sounds that have a frequency too high to be heard by humans are called
ultrasounds.
Other animals can hear ultrasounds. For example, dogs have a hearing range that
extends to almost 40,000 Hz. Bats and Dolphins have hearing ranges that can
extend well over 50,000 Hz.
Loudness and Decibels
BE AWARE! Constant exposure to loud sounds can damage your hearing. People that
work in loud and noisy environments should wear ear protectors over their ears
to avoid any damage to their ears. Loudness of sound is measured in decibels.
Circuits
There are a number of circuit symbols that you should know. Do you know all of
the symbols below?
Symbols
Below are some examples of circuits. Can you answer the following questions
correctly?
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