Sources:AGS Physical Science

http://www.bbc.co.uk/scotland/education/bitesize/standard/physics/waves/wave_definitions_rev1.shtml

What is a wave?

• Waves are vibrations moving from one place to another.

• Waves carry energy from one place to another.– Because waves carry energy, they can be

used for communication (ex: radio and television waves) and to transmit signals.

• There are many types of waves (sound, light, etc).

What is a wave?

• For some types of waves, the medium that carries them has to be matter, either solid, liquid or gas.

• Water waves obviously have to travel in water! • Sound waves need a solid, a liquid or a gas to

travel in.

• The waves in the electromagnetic spectrum (light) do not need any matter to travel in, they are able to travel in a vacuum.

Transverse waves

• the particles of the medium vibrate at right angles to the direction that the energy travels. – This is where the name transverse

comes from - it means 'across'. – All of the electromagnetic waves are

transverse waves, as are water waves.

• Illustration of transverse waves

Longitudinal waves

• Sound waves are longitudinal waves– the energy travels along in the same

direction as the particles vibrate. • This type of wave is known as a longitudinal

wave, so named because the energy travels along the direction of vibration of the particles.

• Illustration of longitudinal wave

Frequency, wavelength, amplitude and wave speed

amplitude• Symbol is = a• is the distance from the center line (or the still

position) to the top of a crest or to the bottom of a trough.

• is measured in meters (m). • The greater the amplitude of a wave then the

more energy it is carrying.

wavelength• symbol is a Greek letter lambda = λ• is the distance from any point on one wave to the

same point on the next wave along. • Wavelength is also measured in meters (m) - it is a

length after all.

frequency• Symbol is = f• is the number of waves passing a point in a

certain time. – We normally use a time of one second, so this

gives frequency the unit hertz (Hz), since one hertz is equal to one wave per second.

A note on Hertz

–For water waves and sound waves the unit hertz is usually good enough but radio and TV waves have such a high frequency that the kilohertz (kHz) or even the megahertz (MHz) are better units.

Speed (also called velocity)

• Symbol = v• is how far the wave travels in a certain time

– Wave speed is measured in meters per second (m/s).

• All the electromagnetic waves travel at 300,000,000 meters per second (3 x 108 m/s).

• Sound travels at about 340 meters per second.

Wave relationships

Wave speed equation• When distance is measured in meters (m)

and time in seconds (s), the speed is in meters per second (m/s).

The speed of sound

The speed of sound is different for different materials – Sound travels fastest

through solids and slowest through gases such as air.

•Task – “What does it matter” lab

Sound

• Sounds are carried by longitudinal waves – the particles of the medium vibrate in

the same direction as the energy of the sound is carried. (bottom diagram)

Task:

review lab Squish in motion

Sound• Humans can hear

sounds in the range 20 hertz to 20 000 hertz. – referred to as the

range of hearing. • Not everyone can hear

over all of this range - the numbers are only approximate. In particular the high frequency limit reduces with age.

Sound

• The loudness of a sound is a measure of the amplitude of the wave. The greater the amplitude, the louder the sound.

• The pitch of a sound is a measure of the frequency of the wave. The higher the frequency, the higher the pitch.

• Task: Straw sounds lab & test tube xylophone

Sound and noise

• The loudness of a sound is a measure of the amplitude of the wave. – The greater the amplitude, the louder

the sound.

• The pitch of a sound is a measure of the frequency of the wave. – The higher the frequency, the higher the

pitch.

Noise

•Unwanted background sounds are sometimes called noise. –When the sound level of this noise rises to higher levels, we refer to this as noise pollution.

Noise

• Sound levels are measured on a scale known as the decibel (dB) scale. – The higher the number the greater is the

sound level. • Too much noise can damage hearing.

– Exposure to 90 decibel sound levels for a long time can cause permanent hearing loss.

– Exposure to a brief sound level of 140 decibels will cause pain and can cause permanent damage to hearing.

Sources of sounds and their db level

Source of sound Sound level in decibels

threshold of Sound 0

whispering 20

background noise at home 40

normal talking 60

noise pollution level 90

pneumatic drill - 5 metres away 100

at a club - 1 m from a loudspeaker 120

threshold of pain 140

ultrasounds

Ultrasounds are• high frequency vibrations beyond the range of

human hearing. – The frequency of ultrasounds is greater than 20,000

hertz.

• transmitted by means of longitudinal waves. • used in medicine to break up kidney stones and

gall stones. It is also used to create images of an unborn baby in a womb.