Science
Waves
Adding and cancelling waves
Sound waves
Pressure waves
Detecting sounds
Light
Detecting light
The pinhole camera
Coloured light
Pressure waves transfers energy from places to places
Sound with a frequency more than 20,000 Hz is called an ultra sound
it is too high pitched for humans to hear but other animals can hear it
Ultrasound has many applications in medicine, including ultrasound scans to check on the health of unborn babies.
Ultrasound can also be used for physiotherapy
Ultrasound can be used to clean jewellry
Cancelling
Adding
If two waves meet eachother out of step, they cancel out
If two waves meet in step, they add together and reinforce eachother. They produce a much higher wave, a wave with a much higher amplitude.
Sound waves are reflected by surfaces.
Hard surfaces reflect sound well, so it makes an echo.
Soft surfaces, like curtains and carpets, reflect very little sound. They absorb sound instead, resulting in no echoes.
Microphones
We can detect sound from our ears
An ear has an eardum inside, connected to three small bones.
The vibrations in the air make the eardrum vibrate, and these vibrations are passed through the three small bones to the cochlea.
Signals are passed from the cochlea to the brain through the auditory nerve, and our brain interprets these signals to sound.
Sound frequency (pitch) is measured in hertz, and humans have an auditory range from 20 Hz to 20,000 Hz.
Mobile phones and telephones contain microphones.
These devices contain a diaphragm, which does a similar job to the eardrum.
The vibrations in the air make the diaphragm vibrate, and these vibrations are changed to electrical pulses.