Unit 4 - Waves Flashcards
What frequency is too low for the human ear to detect?
20Hz
What are sounds too low for the human ear to detect called?
Infrasounds
Which can travel further: infrasounds or ultrasounds?
Infrasounds
Give an animal that can hear infrasounds
Elephants
What are seismic waves?
Vibrations caused by earthquakes.
What waves do earthquakes and volcanoes create?
Infrasounds and sounds we can hear
What is a seismometer?
A piece of equipment used to detect seismic waves
What 2 types of waves are seismic waves
Longitudinal (P waves)
Transverse (S waves)
What can longitudinal waves be transmitted through
Solids, liquids and gases
What can transverse waves that need a medium to travel through be transmitted by
Only solids
Name for main parts of the Earth
Crust, mantle, outer core (liquid), inner core (solid)
What information do you scientists use to model the paths the waves have taken through the Earth
The time the waves arrive in different places and the speed of the waves in different types of rocks
What are shadow zones
When S waves or P waves are not detected on the other side of the Earth to the earthquake
How is and S-wave shadow zone formed
S waves refract as they passed through the Earth however when some S waves reach the liquid core they cannot be transmitted through it and the waves are absorbed leaving the other side without waves
How are P-wave shadow zones formed
This is a band around the Earth. Most waves would be reflected as they pass through the Earth however some are refracted differently when they reach the liquid core. This leaves a larger gap or band between the normal waves and the ones through the liquid core.
Why might weak P-waves arrive in the P-wave shadow zone
If waves in the liquid core have been refracted by something solid
What is the highest frequency that human ears can detect
20,000 Hz
What is ultrasound
Sounds made by Waze with higher frequencies than 20,000 Hz
What do dolphins and bats use ultrasound for
To detect objects around them
What is Sonar
Equipment carried on ships or submarines that uses ultrasound to find the depth of the sea or to detect fish
How does Sonar work
A loudspeaker on the ship emits a pulse of ultrasound which spreads through the water. Some of it is reflected by the seabed. A special microphone on the ship detects the echo and the sonar equipment measures the time between the sound sent and the echo returning.
Apart from detecting, what can ultrasound be used for
To make images of things inside the body such as unborn babies
How does an ultrasound scan work
A gel is used to stop the ultrasound just reflecting from the skin. The probe emits and receives ultrasound scans. Some sound is reflected when the ultrasound waves pass into a different medium such as fat or bone. The ultrasound machine detects the time between sending the pulse and receiving the echo and the display shows where the echoes confirm which creates the image.
What waves are soundwaves
Longitudinal waves
What happens to the particles in a longitudinal wave
The particles in a gas or liquid vibrate backwards and forwards as the soundwave passes but when they reach a solid some energy is reflected as some is transmitted or absorbed
What does a soundwave cause on the surface of a solid
Changes in pressure which causes particles in the solid to vibrate. The disturbance is passed from the Earth with the solid. The vibrations in the solid can be passed on both as longitudinal waves and transverse waves
What determines how vibrations of different frequencies affect solids
The shapes and properties such as density and stiffness
Give the stages of how we hear things
Soundwaves enter the ear canal.
Soundwaves make the eardrum vibrate (a thin membrane)
Vibrations are passed on to tiny bones which amplify them
Vibrations are passed on to the liquid inside the cochlea
Tiny hairs in the cochlear detect the vibrations and create electrical signals called impulses.
Impulses travel along neurones in the auditory nerve to reach the brain
Approximately how big is the cochlea
9 mm
What is the cochlea
A coiled tube containing a liquid
What range of sounds can the human ear detect
From 20 Hz to 20,000 Hz
Describe the cochlea if it was unwound
The base is at the start and is thicker and detects high frequencies
The membrane contains the hair cells
The apex is at the end and is thinner and detects low frequencies
What makes different parts of the membrane vibrate
The frequency of the soundwave is in the liquid inside the cochlea as different thicknesses of the membrane vibrate best at different frequencies
What is the purpose of the tiny hairs
They detect the vibrations and each is connected to a neurone that sends impulses to the brain
What four things can happen when a wave reaches an interface
Reflected, reflected, transmitted and absorbed
Why do some objects appear lighter than others
They reflect more light
Why do some objects appear darker than others
They absorb more light
What light is from lightbulbs or the sun
White light
What are colours
Different frequencies of white light
Why can a prism be used for split up visible light into the colours of the rainbow
Different colours and light change speed by different amounts when they travel from air to glass or vice versa. This means they are refracted through different angles so they are split up
How can we hear echoes
When sound is reflected by a hard surface
Can sound waves be refracted
Yes, when it goes into different materials
What is wave velocity equal to
The frequency multiplied by the wavelength
When does the frequency of a soundwave change
When we hear sounds of different pitches
When does the wavelength or velocity of a soundwave change
If the sound has a same pitch and we hear it through a different material
What happens to like travelling along the normal when it goes into a different medium
There is no change in direction
Why do objects of the bottom of a swimming pool look closer than it really is
Light reflected by it changes direction when it leaves the water
What affects the bend of the light
How fast the light travels in the two media and the angle of the light hitting the interface
What will make the light bend more
If the difference in speed is greater between the two media
What direction does the light bend when it slows down
Towards the normal
What waves can we use to help us understand what happens when light waves
Waterwaves
What affects the speed of water waves?
The depth of the water
What will happen to waves from deep to shallow?
They will slow down and change direction - towards the normal
Why is it impossible to take pictures of things that are deep down in the seabed
Light waves don’t travel very far in seawater as they are either absorbed or reflected by tiny particles in the water
Explain the core practical - investigating waves on water
Set up a ripple tank with a straight dipper at one end of the tank and fasten a ruler to one of the adjacent sides above water level
Very the voltage to the motor until you can only see two ways along the ripple tank
Count the waves formed in 10 seconds and write it down
Use the ruler to estimate the wavelength and calculate the speed using the length and the frequency
Mark two points on the ruler and measure the distance and use the stopwatch to find the time it takes for a wave to go from one mark to this information to calculate the speed.
Explain the core practical – investigating waves in solids
Suspend a metal rod horizontally using a clamp and rubber bands
Hit one end with a hammer. Hold a smart phone with a frequency at near the rod and note down the peak frequency
Measure the length of the road and the wavelength will be twice the length of the rod
Use the frequency and wavelength to calculate the speed of sound in the rod
What is the equation for wave speed
Wave speed (m/s)= frequency (Hz) x wavelength (lambda)
What is the speed of light in a vacuum
300,000,000 m/s
Describe a way of measuring the speed of waves on water
Measuring the time it takes for a wave to travel between two fixed points such as buoys. The speaker can be calculated from the time and distance
What waves are water waves
Transverse
How is energy transferred in waterwaves
Particles in the water move up and down as a wave passes – they are not carried to the shore
What waves our sound waves
Longitudinal
How is energy transferred in longitudinal waves
Particles in the material move backwards and forwards as the wave passes in the same direction the wave is travelling
What ways do not need a medium to travel through
Electromagnetic waves
For soundwaves, what does the frequency determine
The pitch
What is the period
The length of time it takes one wave to pass a given point
What is the ampliture
Maximum distance of a point on a wave from its rest position in metres
What does the amplitude determine
How loud the sound is
