TOPIC 4 - WAVES Flashcards
what are waves
Waves transfer energy and information without transferring matter
Transverse vs longitudinal waves
- Longitudinal waves move parallel to direction of energy transfer
- Transverse waves move perpendicular to direction of energy transfer
- Longitudinal have compressions and rarefactions
- Transverse have peaks and troughs
- Longitudinal waves move in solids liquids gases
- Transverse waves move in solids only
What is frequency
Number of wave cycles per second
What is wavelength
Distance peak to peak or compression to compression
What is period
Time taken to complete one wave cycle
Equation linking time and frequency
Time = 1/f
Frequency = 1/T
What is amplitude
Maximum displacement a point moves from rest position
Equation for wave speed
frequency x wavelength
or
distance/time
What can happen to waves when meeting a boundary?
- Reflected
- Refracted
- Transmitted
- Absorbed
What is reflection
When wave ‘bounces off’ boundary and stays in their original medium.
What is refraction
When wave changes speed and direction betweem 2 materials of different densities.
What happens to light ray if moving from a less dense to a more dense medium
It slows down and refracts towards normal.
What types are waves are sound waves
Longitudinal
What happens when sound waves are passed through liquids and gases?
particles vibrate back and forth as wave passes through.
What happens when sound waves are passed through solids?
Some energy is reflected, transmitted or absorbed. The sound wave causes changes in pressure on surface of the sold. It causes the particles in solid to vibrate (vibrations in solid can be longitudinal/transverse)
How does the human ear detect sound waves?
- sound waves enter ear canal
2 sound waves make eardrum (thin membrane) vibrate - Vibrations are passed onto ossicles (tiny bones) that amplify vibrations
- Vibrations are passed to liquid inside cochlea
- Tiny hairs inside cochlea detect vibrations and create impulses (electrical signals)
- Impulses travel along neurones in auditory nerve to reach the brain
What is ultrasound
Frequency above 20 000Hz
What is infrasound
Frequency below 20Hz
What frequencies can humans detect
20-20 000Hz
What are some uses of ultrasound
- Sonar
- Foetal scanning
How does sonar work?
It uses ultrasound to detect objects underwater.
The pulse of ultrasound is sent underwater and is reflected off the ocean bottom.
The tiem it takes for the sound wave to return can be used to calculate depth.
How does foetal scanning work?
- Gel is used on the stomach to stop ultrasound just reflecting off the skin.
- The transducer emits and recieves ultraosund waves.
- Some waves are reflected back to the transducer when reaching different mediums like fat or bone.
Why is foetal scanning safe?
It is not ionising like X-rays.
What type of waves do earthquakes produce?
P-waves and S-waves
Compare P-waves and S-waves
- Pwaves are longitudinal (can pass thru solids annd liquids)
- Swaves are transverse (only thru solids)
- S-waves can’t travel through (liquid) outer core
-P waves can - P-waves are faster, S-waves are slower
How are seimsic waves detected?
They are detected by seisometer all around Earth.
What are the discoveries made by seismic waves?
- On the opposite side of the Earth to an earthquake, only P-waves are detected, not S-waves, suggesting mantle is solid as both waves pass through it, and suggesting outer core is liquid as no S-waves can penetrate it.
- Refractions between layers cause 2 shadow zones, where no P-waves are detected, suggesting inner core is solid as size and positions of these shadow zones indicate large refraction taking place.
What happens when sound waves moves from less dense to more dense medium?
The wavelength decreases, frequency stays the same, speed decreases
