P12 Wave Properties

Question 1

What is an oscillation?

Answer 1

The repeated and regular fluctuations, above and below the same position, eg the pressure of a sound wave or the voltage of an alternating current.

Question 2

What are vibrations?

Answer 2

Repeated movements back and forth (about a fixed point)

Question 3

What is a longitudinal wave?

Answer 3

A wave that moves parallel to the direction in which the particles are vibrating.

Question 4

What is a transverse wave

Answer 4

A wave that moves in a direction perpendicular to the way in which the particles are vibrating.

Question 5

What is the difference between mechanical and electromagnetic waves?

Answer 5

Mechanical waves cause oscillations of particles in a solid, liquid or gas and must have a
medium
to travel through. Electromagnetic waves cause oscillations in electrical and magnetic fields.

Question 6

Key words about waves:

Answer 6

rest position - the undisturbed position of particles or fields when they are not vibrating
displacement - the distance that a certain point in the medium has moved from its rest position
peak - the highest point above the rest position
trough - the lowest point below the rest position
amplitude - the maximum displacement of a point of a wave from its rest position
wavelength - distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
time period - the time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough
frequency - the number of waves passing a point each second

Question 7

What is the formula for time period?

Answer 7

T=1/f
T= is period (s)
f is frequency(Hz)

Question 8

What is the formula for wave speed?

Answer 8

wave speed = frequency × wavelength

This is when:

wave speed (v) is measured in metres per second (m/s)
frequency (f) is measured in Hertz (Hz)
wavelength (λ) is measured in metres (m)

Question 9

How to calculate the speed of sound

Answer 9

use speed formula
v=s/t

Question 10

What are compressions and rarefactions in a longitudinal wave?

Answer 10

An area of increased pressure. In longitudinal waves, the particles in areas of compression are closer together than on average.

An area of reduced pressure. In longitudinal waves, the particles in areas of rarefaction are further apart than on average.

compressions are regions of high pressure due to particles being close together
rarefactions are regions of low pressure due to particles being spread further apart

Question 11

What are examples of longitudinal waves?

Answer 11

Sound waves

Question 12

What are some examples of transverse waves?

Answer 12

ripples on the surface of water

vibrations in a guitar string

a Mexican wave in a sports stadium

electromagnetic waves - eg light waves, microwaves, radio waves

seismic S-waves

Question 13

What can all electromagnetic waves do?

Answer 13

transfer energy as
radiation
from the source of the waves to an absorber
can travel through a
vacuum
such as in space
travel at the same speed through a vacuum or the air

Question 14

What is a spectrum?

Answer 14

A series of similar waves arranged in order of wavelength or frequency.

Question 15

What is a wave?

Answer 15

Vibrations that transfer energy from place to place without the transference of matter.

Question 16

What is the angle of incidence?

Answer 16

Angle between the normal and the incident ray.

Question 17

What is the angle of reflection?

Answer 17

The angle between the reflected ray and the normal (the imaginary line drawn at 90 degrees to the reflecting surface).

Question 18

What is the normal?

Answer 18

An imaginary but useful line at right angles to the boundary between air/glass. All angles are measured to this line.

Question 19

What is a plane?

Answer 19

A flat, two-dimensional surface.

Question 20

What is diffuse reflection?

Answer 20

If a surface is rough,
diffuse reflection
happens. Instead of forming an image, the reflected light is scattered in all directions. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.

Question 21

What is refraction?

Answer 21

Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens.

Question 22

What is a wavefront?

Answer 22

This is an imaginary surface that we draw to represent the vibrating part of a wave.

Question 23

What is a ripple tank?

Answer 23

A ripple tank is a transparent shallow tray of water with a light shining down through it onto a white card below.

The light allows you to see the motion of the ripples created on the water’s surface more easily.

Ripples can be made by hand but to generate regular ripples it is better to use a motor.

Question 24

The higher the density of the material that light passes through the slower the _____?

Answer 24

Speed of light wave

Question 25

angle of incidence =

Answer 25

angle of reflection

Question 26

What determines a sounds loudness?

Answer 26

Amplitude

Question 27

What is the pitch of the sound based on?

Answer 27

Frequency

Question 28

Why can’t sound travel through a vacuum?

Answer 28

Sound cannot travel through a
vacuum
because there are no particles to carry the vibrations.

Question 29

Speed of sound

Answer 29

around 340m/s

Question 30

What is an oscilloscope?

Answer 30

A device used to record signals that change regularly, such as sound or other vibrations.

Question 31

What is the human hearing range?

Answer 31

The range of normal human hearing is 20 Hz to 20,000 Hz (or 20 Hz to 20 kHz).

Question 32

What is doubled when an echo is heard

Answer 32

the distance

Question 33

How does the ear hear sound?

Answer 33

The human ear detects sound.

Sound waves enter the
ear canal
and cause the eardrum to vibrate.

Three small bones transmit these vibrations to the
cochlea
.

This produces electrical signals which pass through the
auditory nerve
to the brain, where they are interpreted as sound.

Question 34

What are the advantages of using ultrasound imagery?

Answer 34

Ultrasound waves pass through tissue without causing harm, unlike x-rays which can damage DNA inside cells.
Ultrasound equipment is relatively cheap, portable and easy to use.
Images of internal organs can be seen without having to operate on patients.

Question 35

What are the medical uses of ultrasound?

Answer 35

Medical uses of ultrasound
The best known example of the use of ultrasound is medical imaging, to ‘see’ inside a body.

An ultrasound scanner is simply run over the skin to obtain an image of what’s inside.

The scanner probe has a built-in transducer that directs ultrasound pulses down into the body.

As the waves travel through the different bones and tissues, some are reflected off a boundary but some travel further to be reflected back up again off another boundary as some parts have different densities.

some of the ultrasound waves are reflected at a boundary;
the time taken for the waves to leave a source and return to the detector is measured;
the depth of the boundary can be determined using distance = speed of sound in the material x the time taken.

The probe receives the reflected waves and a computer connected to the scanner uses them to draw an image on a screen.

Scans of foetuses (unborn babies developing in the womb) are made this way and are used, for example, to measure the diameter of the head of a foetus so that growth can be monitored.

Ultrasound imaging also helps to diagnose problems with the:

heart;
kidneys;
blood vessels;
bladder.
The best known non-imaging medical use of ultrasound is the breaking of kidney stones.

The vibrations caused by the ultrasound shake apart the kidney stones, breaking them up.

Question 36

What are some industrial uses of ultrasound?

Answer 36

Materials can be tested for internal faults and cracks that could lead to the failure of a structure under certain conditions.

Ultrasound imaging provides a quick method of detection and perhaps prevents serious accidents.

Ultrasound can be used to clean jewellery.

The vibrations caused by the ultrasound shake apart the dirt, breaking it up.

Question 37

What does SONAR stand for?

Answer 37

SOund Navigation And Ranging

Question 38

What are seismic waves?

Answer 38

Shock waves travelling through the Earth, usually caused by an earthquake.

Question 39

What are the 2 types of seismic wave?

Answer 39

P-waves, which are
longitudinal waves
S-waves, which are
transverse waves

Question 40

What are the differences?

Answer 40

A P wave is longitudinal and can travel through liquid and solids and they are faster.
A S wave is transverse and can only travel through Solids.

Question 41

How does P waves and S waves influence the way we think the earth is structured.

Answer 41

The study of seismic waves provides evidence for the internal structure of the Earth, which otherwise cannot be observed directly.

Seismic waves from large earthquakes are detected around the world. Their paths are curved as the waves refract due to the gradually changing density of the layers.

S-waves are not detected on the opposite side of the Earth - this suggests that the mantle has solid properties, but the
outer core must be liquid.
P-waves are detected on the opposite side of the Earth. Refractions between layers cause two shadow zones where no P-waves are detected. The size and positions of these shadow zones indicate there is a solid inner core.

Question 42

Why are the sides of a ripple tank sloped?

Answer 42

They prevent reflection at the sides.

Question 43

Example Question
A string of stretched length 1.24m was made to oscillate and 3 equal loops were seen at frequency 180Hz.
A)Calculate the wavelength of the waves on the string
B)Calculate the speed of the waves on the string

Answer 43

A) wavelength
1.24x 2/3=0.827m
B) 180x0.827=149m/s

Question 44

Example question 2
A depth finder was used to measure the depth of the sea.It took 0.36 seconds for the pulse to ping back.Calculate the depth of the bed when the speed of sound is 1350m/s

Answer 44

distance to sea bed and back = 1350 m/s × 0.36 s = 486 m
distance to sea bed = 0.5 × 486 m = 243 m

Question 45

Required practical youtube link:

Answer 45

https://www.youtube.com/watch?v=OY0lXHPo_nM&ab_channel=MalmesburyEducation