P5.1 grey - new Flashcards by Marlon Dassanayake

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

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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

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Snapshot - distance from one point on a wave to the same point on the next is?

Wavelength

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Amplitude in time trace / snapshot

Middle to the top/bottom(trough) of a wave

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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

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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

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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

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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

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3 wave phenomena

Reflection - waves reverse direction
Refraction - waves change direction/bend
Diffraction - waves spread out

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Medium

(Plural media) is a region of space of the same material/density

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Wave phenomena only occur when (2)

at the boundary between 2 media
when a wave changes speed

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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)

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Reflection - definition

Reflection is the wave phenomenon by which a wave reverses direction as it meets the boundary between two media.

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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

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PIC

Reflection - 1 line, 2 rays, 2 angles
W/ray diagram

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Plane mirror

A mirror which is perfectly flat( and reflects all of the light incident upon it)

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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

PIC

PIC

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

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

PIC

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

PIC

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

P5.1 grey - new Flashcards

Incl some non-greybits