P5.1 grey - new Flashcards
Incl some non-greybits
There are 2 ways to represent a wave
1 - a time trace shows how displacement varies with time at a particular position
2 - a snapshot of a wave shows how displacement varies with distance at a particular time
Time trace - time for a wave to complete one oscillation is?
/ point for a wave to same point on next wave
Time period of the wave
Snapshot - distance from one point on a wave to the same point on the next is?
Wavelength
Amplitude in time trace / snapshot
Middle to the top/bottom(trough) of a wave
To measure the velocity of sound - clap
Time how long it takes to hear an echo of a clap when yo are at a distance from a wall , work out velocity - distance, velocity, time
To measure the velocity of sound - alternate
Connect a pair of microphones a certain distance apart to an oscilloscope
- know the distance between the microphones and the time for the sound to travel between them to calculate velocity
As sound is a longitudinal wave, when you see the trace of a transverse wave on the screen of an oscilloscope, it is showing ?
Variation of pressure with time, not the sound wave itself
The velocity of sound can vary w/ (2) and why
- temperature and pressure
- this is because these factors affect the velocity at which the disturbance in the wave is transferred between particles
3 wave phenomena
Reflection - waves reverse direction
Refraction - waves change direction/bend
Diffraction - waves spread out
Medium
(Plural media) is a region of space of the same material/density
Wave phenomena only occur when (2)
- at the boundary between 2 media
- when a wave changes speed
When waves cross a boundary, what changes, what doesnt
- speed will change
- frequency never changes
- wavelength will change
(According to wave equation, as speed changes)
Reflection - definition
Reflection is the wave phenomenon by which a wave reverses direction as it meets the boundary between two media.
Reflection - rules
(2)
We always consider plane (smooth) surfaces such as mirrors, which obey the law of reflection.
“The angle of incidence, i is equal to the angle of reflection, r”
i = r
PIC
Reflection - 1 line, 2 rays, 2 angles
W/ray diagram
.
Plane mirror
A mirror which is perfectly flat( and reflects all of the light incident upon it)
Law of reflection
“The angle of incidence, i is equal to the angle of reflection, r”
i = r
- true only for planer mirrors
The image formed by a mirror can be shown using __
You need __ from the object .
You then ____ back into the mirror
Ray diagram
2 incident rays from the object
Project the 2 reflected rays back into the mirror
P5.3.1
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If the angle of reflection of a light ray from a plane mirror is 20, what is;
the angle of incidence?
the angle between the incident ray and the reflected ray?
20 by The Law of Reflection
40
REFRACTION DEFINE
Refraction is the wave phenomenon by which a wave changes direction (bends) as it crosses the boundary between two media.
Refraction explanation
As waves cross a boundary between two different media… … their speed changes… … their direction changes… … they are observed to bend.
PIC
REFRACTION RAY DIAGRAM from air to glass
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Refraction - 2 rules
Waves bend TOWARDS THE NORMAL when they pass from less dense to more dense medium (when they slow down)
Waves bend AWAY FROM THE NORMAL when they pass from more dense to less dense medium (when they speed up)
COMPLETE PIC
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Ultrasound - what (+ consideration)
The name given to sound waves with a frequency grater than 20,000Hz
Can’t be heard because outside human audible range of 20Hz - 20 kHz
Ultrasound scans -2 uses
PIC
- to image a baby inside a womb
- detecting cracks is in metal pipes and buildings
How ultrasound scans work (3)
PIC
- the transducer is a device that produces ultrasound waves by causing a crystal to vibrate very rapidly
- the ultrasound waves are partially reflected every time they cross a boundary between different media
- the reflected ultrasound waves return to the transducer as a series of pulses, which are deciphered to form an image (the machine calculates the distance using time and velocity, and uses those distances to produce an image)
An o__ t__ of ultrasound wave echoes can be used to calculate the __/__/__ of the various __ and __.
An oscilloscope trace of ultrasound wave echoes can be used to calculate the distance/depths/lengths of the various tissues and boundaries.
PIC
Pulses in an oscilloscope (2)
The first recorded pulse is always the reflection of the transmitted pulse as it crosses into the body.
Pulses after that originate from reflections at boundaries.
Depth of boundary - equation
= (speed of the ultrasound waves) x (transit time) x ½
Sonar
Used by submarines and fishermen to find distances using the time for an echo and the speed of sound in water.
Doctors also use ultrasound to -2
Find kidney stones, and monitor blood flow
Whenever light passes between media along the normal line…
It doesn’t refract ,.. it passes straight through
The ear is designed to - 3
Detect, amplify, and convert sound to an electrical signal
How the ear detects sound - 5 steps
1- the pinna and auditory canal gather the sound wave; direct sound into the ear drum
2- the ear drum vibrates, and causes the ossicles to vibrate; vibrations of sound wave amplified
3- cochlea transmits vibrations to small hairs
4- hairs are attached to sound-detecting cells
5- cells release chemicals when stimulated, electrical signal sent to brain via auditory nerve
Why does the human ear have an audible range - 4
- Any body that vibrates, has a natural frequency.
- The natural frequency of an object is the frequencyat which it can (physically) vibrate.
- The human ear drum can only vibrate between 20Hz and 20,000Hz… it is unable to vibrate any slower or faster than these limits.
- Thus, the human audible range is only 20hz-20,000Hz
Why sound dies away- wal;
Absorbed
When sound absorbed, it makes the particles in the wall vibrate —> wall gets bit hotter
When a microphone absorbs sound wave?
Diaphragm can move —> produces a changing electrical signal
explain why such processes only work over a limited frequency range, and the relevance of this to human hearing
The hairs in the human cochlea have different lengths and vibrate at different frequencies of sound. This is how the human ear puts together an electrical signal that contains all the different frequencies in the sound wave being received.
The range of frequencies that a person can hear depends on the range of lengths of hairs in the cochlea.
why hearing (audition) changes due to ageing
As a person ages, the shorter hairs that respond to higher frequencies stop working - this means that people tend to lose the ability to hear higher frequencies of sound as they grow older.
Resonance
Applying a vibration at natural frequency, will result in a vibration with a very big amplitude - called resonance
