Waves 2 * Flashcards
What is the normal?
a line perpendicular to the surface of an object (e.g. mirror or glass block)
drawn as a dotted line
Where are angles measured between?
measured between the normal and the light ray
What is the law of reflection?
the angle of incidence is equal to the angle of reflection
What is specular reflection?
light reflected from a smooth surface at a definite angle
What is diffuse reflection?
reflection produced by rough surfaces that tend to reflect light in all directions
What three things can happen when waves arrive at the boundary of two different materials?
- absorption
- reflection
- transmission
Which material absorbs the wave?
Which store is the energy transferred to?
waves may be absorbed by the second material
often the energy is transferred to a thermal energy store
What is reflection?
waves may bounce back (from the second material)
What is transmission?
waves may carry on travelling through the new material and often undergo refraction
Which two factors depend on what happens to the wave when it reaches a boundary?
its wavelength
the properties of the materials involved
What is refraction?
a wave can change direction when it meets a boundary between two objects
What is TIR?
Total Internal Reflection
when a wave is travelling into a less dense material, the ray can be refracted back into the first material instead of being transmitted into the new material
What is the critical angle?
When the angle of incidence increases and the refracted ray travels along the boundary, the angle of incidence is called the critical angle
When does TIR occur? (2 points)
when light is travelling from a more dense material into a less dense material (e.g. glass to air)
when the angle of incidence is greater than the critical angle
What shape is a convex lens?
oval shaped
What shape is a concave lens?
thinner in the middle, thicker at the top and bottom
What is the focal length?
the distance between the middle of the lens and the focal point
What is the focal point?
where the light rays are focused/meet
Fill the gaps:
- the more powerful a lens is, the ____ the light will be _________ and the _______ the focal length will be
- the more curved a lens is the ____ ________ it is
- the more powerful a lens is, the more the light will be refracted and the shorter the focal length will be
- the more curved a lens is the more powerful it is
Give three points about a real image
- formed when light passes through a lens and comes together to form an image
- the light has formed an image and it can be projected onto a screen
- e.g.s projector image on the retina
Give three points about a virtual image
- formed when light from an object doesn’t actually come together to form the image but the image is created where the light appears to come together
- the image can’t be projected onto a screen
- e.g.s image in a mirror, looking through a magnifying glass
How are sound waves produced?
by vibrations
What type of wave are sound waves?
longitudinal
How do sound waves transfer energy?
mechanically
Which state of matter do sound waves travel fastest in?
solids
because the particles are close together so collisions happen quickly
Where can’t sound waves travel?
in a vacuum (e.g. space) because there are no particles
Give two properties of sound waves
sound waves can be reflected - this is an echo
sound waves can be refracted - when they travel from a less dense material into a more dense material the sound speeds up which causes it to change direction
Where are echos strongest and weakest?
-strongest off of solid surfaces as their energy is not absorbed well
- weakest off of soft materials where their energy is absorbed as the particles in the material can move more easily
What is frequency?
the number of wave, oscillations or vibrations per second (measured in Hz)
What is sound above 20,000 Hz called?
ultrasound
What is the hearing range for humans?
20 Hz to 20,000 Hz
What is sound below 20 Hz called?
infrasound
What does the auditory nerve do?
sends electrical impulses to the brain
What does the cochlea do?
converts the vibrations into electrical signals sent to the brain via the auditory nerve
What does the ear canal do?
transmits sound waves to the ear drum
What does the ear drum do?
vibrates with the frequency of the sound wave and transmits the vibrations to the ossicles
What does the eustachian tube do?
allows the pressure inside the ear to be balanced with the pressure outside the ear
What do the ossicles (hammer, anvil and stirrup) do?
vibrate and these vibrations are passed to the cochlea
What does the pinna do?
it funnels the sound into the ear cannal
What do the semi-circular canals do?
vibrations pass through here to the cochlea and help you keep your balance
What is the central membrane?
the membrane in the centre of the cochlea that controls the frequencies vibrating along it and has basilar that detect the vibration and convert it into electrical signals that send impulses to the brain
Why does the membrane have a range of stiffness/thickness?
so that the membrane can vibrate more or less at different frequencies
What is ultrasound used in?
- echo location
- sonar
- medical scans
- exploring structures
How are medical scans carried out? (using ultrasound)
Fill the gaps:
- an __________ probe is placed on the skin of the patient
- the probe sends pulses of ______ _____ through the body of the patient
- when the _____ ____ meets a _______ of different mediums, some of the _____ are ________
- the computer detects the time between the pulses and the echoes and produces an _____
- an ultrasound probe is placed on the skin of the patient
- the probe sends pulses of sound waves through the body of the patient
- when the sound wave meets a boundary of different mediums, some of the waves are reflected
- the computer detects the time between the pulses and the echoes and produces an image
What is infrasound used in? (seismic waves) and how
measuring the structure of the earth
- using seismic waves produced by an earthquake scientists can study the structure inside the earth
- they track the time and space P waves and S waves are detected around the earth
What are S waves?
slow moving transverse waves that travel only through solids
What are P waves?
fast moving longitudinal waves that travel through liquids and solids
What is echolocation?
animals use echolocation for navigating and finding food - they send out sound waves and when they reflect from an object they travel back to the animal, the animal listens to the echo and depending on the time between the sound being sent and received they can detect how far away objects are
What is sonar?
its used by ships and submarines to find the depth of the ocean or to locate fish - the ship sends out sound waves and then records the time between the signal being sent and received, and the speed of the wave is known so the distance can be calculated using distance = speed x time and then divided by 2
What is the method to measure the speed of sound? (4 steps)
1) two people stand 100m apart - one with stopwatch and one with two blocks
2) the person with the blocks claps them together whilst the other person starts the stopwatch
3) the person with the stopwatch stops it when they hear the blocks
4) use the equation speed = distance x time to find the speed of the sound
