Download Waves transfer energy without transferring matter. There are two

Waves transfer energy without transferring matter.
There are two main kinds of waves, transverse and longitudinal.
In transverse waves, the oscillation is at right-angles to the direction in which energy travels. Waves
along a rope, light waves and waves on water are all examples of transverse waves.
Wavelength ( λ) is the distance from the crest of a wave to the crest of the next wave (the length of
each complete wave, measured in metres ).
Amplitude is the distance from the crest of a wave to the place where there is no displacement.
In longitudinal waves, the oscillation is in the same direction as the direction in which the energy is
carried. Sound is a longitudinal wave.
The frequency (f) of a wave is the number of waves produced each second. The unit of frequency is
hertz (Hz).
The wave speed equation is :
Wave speed (m/s) = frequency (Hz) x wavelength (m)
V = f x λ
Sound can be transmitted through solids, liquids or gases, but not through empty spaces (vacuum).
Sounds are made when objects vibrate.
When an object vibrates, the air around it is made to vibrate. The particles in the air alternately
come closer together, creating a compression, and then spread further apart. The sound spreads
through the air.
The particles vibrate with the same frequency as the sound and in the same direction as the sound
travels. So, we call sound waves longitudinal.
The energy of the sound causes other objects to vibrate. The sound makes your eardrums vibrate,
this is how you detect sounds. These vibrations are passed to the inner ear along three small bones
called the ossicles. Humans can hear sounds that have frequencies from about 20Hz to about
20 000Hz. But not everybody can hear the entire range. Older people may not be able to hear higher
frequencies as well as younger people.
The lower the frequency of the sound, the lower the pitch of the note. The greater the frequency,
the higher is the pitch of the sound produced.
The bigger the amplitude of the vibration, the louder the sound. If the sound is too loud, the large
vibration may damage your ear. Exposure to loud sounds for long periods can cause hearing loss
(deafness) because the excessive movement of the ossicles causes them to wear down quickly!
Sound levels are measured in decibels (dB).
Ultrasound- sounds that have too high frequency for humans to hear (above 20 000 Hz).
Ultrasound is partly reflected when it meets the boundary between two different materials. The
reflected wave is used to build up a picture of the inside of the body. Ultrasound scans are used to
look at babies before birth and also to look at other organs.
Bats and dolphins use echolocation to detect objects around them They detect the echoes from
‘clics’ they emit and calculate the distance away of the object.
Ultrasound is used in industry (e.g. cleaning small objects), medicine (e.g. USG), army (manouvers).
TASKS
1.
2.
3.
4.
5.
6.
7.
a)
b)
c)
What is the difference between transverse and longitudinal waves – give an example of each.
What is the relationship between the frequency f, the speed v and the wavelength λ of a wave ?
A musical note has a frequency of 440Hz.The wavelength of the sound is 0.75m. Calculate
the speed of sound in air.
The 440Hz note has a wavelength of 3.4m in water. What is the speed of sound in water?
A bat sends a signal out. It is reflected from the wall of the cave 0.2 seconds later. The cave wall
is 30m away. What is the speed of sound?
What property of ultrasound is used to make the image of a baby?
Look at the graph showing the recommended maximum periods during which people should
listen to sounds of different levels.
What is the maximum time each day a person should listen to a personal stereo at 96dB?
In what way could a sound of more than 120dB damage the ear?
Sally works for five hours in a nightclub. What should the maximum sound level be there so that
her hearing is not damaged?
Use the graph to find answers! The graph is on the display (next to Classroom 29)
Vocabulary
amplitude – amplituda
particles - cząsteczki
deafness (hearing loss) – głuchota (utrata
słuchu)
pitch of a note – wysokość dźwięku (nuty)
eardrum – błona bębenkowa
entire range – cały zakres
frequency – częstotliwość
longitudinal - podłużna
ossicles – trzy kosteczki w uchu (młoteczek,
kowadełko i strzemiączko)
reflection – odbicie
transverse – poprzeczna
ultrasound - ultradźwięki
vacuum – próżnia
vibrate – drgać
wave – fala
wavelength – długość fali