topic 6 - waves

state the two types of waves

• transverse

• longitudinal

state examples of transverse waves

• ripples on water surface

• s-waves

• electromagnetic waves

state example of longitudinal waves

• sound waves travelling through air

• p-waves

state the areas longitudinal waves show

• rarefaction

• compression

state definition of a wave

• repeated vibrations

• that transfer energy

state transverse wave definition

• waves where points along its length

• vibrate perpendicular

• to the direction of energy transfer

state longitudinal wave definition

• waves where points along its length

• vibrate parallel

• to the direction of energy transfer

state what waves transfer

• energy

• not particles of the medium

state peak definition

highest point of a wave

state trough definition

lowest point of a wave

state rarefaction definition

longitudinal waves that are spaced apart

state compression definition

longitudinal waves that are close together

state the differences between transverse and longitudinal waves based on structure

• transverse = peaks and troughs

• longitudinal = compressions and rarefactions

state the differences between transverse and longitudinal waves based on vibrations

• transverse = perpendicular to direction of transfer of energy

• longitudinal = parallel to direction of transfer of energy

state the differences between transverse and longitudinal waves based on vacuum

• transverse = only electromagnetic waves can travel through

• longitudinal = no waves can travel through

state the differences between transverse and longitudinal waves based on material

• transverse = can move in solids, liquids and gases

• longitudinal = cannot travel in a vacuum

state the differences between transverse and longitudinal waves based on density

• transverse = constant density

• longitudinal = changes in density

state the differences between transverse and longitudinal waves based on pressure

• transverse = constant pressure

• longitudinal = changes in pressure

state the differences between transverse and longitudinal waves based on speed of wave

• transverse = dependent on material it’s travelling in

• longitudinal = dependent on material it’s travelling in

state amplitude definition

• distance from the undisturbed position

• to the peak of trough

• of a wave

state the symbol and unit of amplitude

• symbol = A

• unit = m

state wavelength definition

• distance from one point

• to the same point

• on the next wave

state how to measure wavelength in transverse waves

• measured from one peak

• to the next peak

state how to measure wavelength in longitudinal waves

• measured from centre of one compression

• to the centre of the next compression

state the symbol and unit for wavelength

• symbol = λ

• unit = m

state frequency definition

• number of waves

• passing a point

• in a second

state the symbol and unit of frequency

• symbol = f

• unit = Hz

state time period definition

• time taken

• for one full cycle

• of a wave

state symbol and unit of time period

• symbol = T

• unit = s

state equation to calculate time period

T (s) = 1 / f (Hz)

state wave speed definition

• speed at which

• energy is transferred

• through the medium

state equation to calculate wave speed

v (m/s) = f (Hz) x λ (m)

describe a method to measure the speed of sound waves in air

• two people stand 100m apart

• distance between them is measured using a trundle wheel

• one person has two wooden blocks, which they bang above their head

• the other person starts the stopwatch when they see the person bang the wooden blocks together

• the other person stops the stopwatch when they hear the sound

• the experiment is repeated multiple times to calculate an average speed

• use equation speed = distance / time to calculate the speed of sound

state the variables in measuring wave properties

• independent = frequency

• dependent = wavelength

• control = same depth of water

state the method to measure the speed of ripples on a water surface

1. set up a ripple tank with a screen and ruler beneath, a light source above and a wooden bar supported by elastic bands in the water

2. fill the ripple tank with a water depth of no more than 1cm

3. turn on the power supply and light source to produce a wave pattern on the screen

4. wavelength of the waves is determined by using the ruler to measure the length of the screen and dividing the distance by the number of wavefronts

5. frequency can be determined by timing how long it takes for a given number of waves to pass a particular point and dividing the number of wavefronts by the time taken

6. record the frequency and wavelength in a table and repeat measurements

7. use the equation v = λ x f to calculate wavespeed

state what increases the rate of energy transfer by waves

more molecules present in the medium

explain what happens in the refraction of sound from a less dense medium to a denser medium

• wavelength increases

• frequency stays the same

• velocity increases

explain what happens in the refraction of sound from a denser medium to a less dense medium

• wavelength decreases

• frequency stays the same

• velocity decreases

explain how the speed of sound in air is affected by temperature

• increased temperature increases the speed of sound waves

• as air molecules have gained kinetic energy

• thus making them move faster

• allowing them to carry sound waves faster

state the variables investigating incidence and reflection

• independent = angle of incidence

• dependent = angle of reflection

• control = distance of ray box from mirror

stated method of the investigation of reflection and refraction

1. set up a piece of paper and a ray box at 45 degrees to a plain mirror

2. use a ruler to mark a 10cm straight line in the middle of the paper

3. use a protractor to draw a 90 degree line that bisects the 10cm line

4. place the mirror on the line

5. switch on the ray box and aim a beam of light at the point of bisection

6. use a pencil to mark a point where the light beam leaves the ray box and a point on the reflected beam about 10cm away from the mirror

7. remove the ray box and mirror

8. use a ruler to join the two marked points to the point of bisection

9. use the protractor to measure two angles from the 90 degree line

10. the angle for the ray towards the mirror is the angle of incidence and the other angle is the angle of reflection

11. repeat the experiment three times with the beam of light aimed at different angles

analyse the investigation of incidence and reflection

• law of reflection states: angle of incidence = angle of reflection

• if the experiment was carried out correctly, angle i and angle r should be the same

state the variables in the investigation of the refraction of light by a perspex block

• independent = angle of incidence

• dependent = angle of refraction

• control = use the same perspex block

state method of the investigation of the refraction of light by a perspex block

1. place the perspex block on a sheet of paper and carefully draw around the block using pencil

2. switch on the ray box and direct a beam of light at the side face of the block

3. mark on the paper: a point on the ray close to the box, point where the ray enters the block, point where the ray exits the block and a point on the exit ray 5cm away from the block

4. draw a dashed line normal to the outline of the block where the points are

5. remove the block and join the points marked with three straight lines

6. replace the block within the outlines and repeat the experiment with the ray box pointed at the block from different angles

7. record these results in a table

state what happens when sound waves travel through solids

vibrations in the solid

state what happens when sound waves travel through the ear

• the ear drum and other parts of the ear vibrate

• causing the sensation of sound

state what restricts the limits of human hearing

• conversion of sound waves to vibrations of solids

• works over a limited frequency range

explain the effect of sound waves on the ear drum

• eardrum is made of skin and tissue

• sound waves travel down the auditory canal towards the eardrum

• pressure variations created by sound waves exerts a varying force on the eardrum

• causing it to vibrate

• vibration pattern of sound creates the same pattern of vibration in the eardrum

explain how the ear converts sound waves into sound

• sound waves travel down the auditory canal towards the eardrum

• pressure variations created by sound waves exerts a varying force on the eardrum

• causing it to vibrate

• vibration pattern of sound creates the same pattern of vibration in the eardrum

• the eardrum vibration is transferred to three small bones

• the vibration of the small bones then transfers to vibrations in the inner ear

• nerve cells in the inner ear detect sound and send a message to the brain

• giving the sensation of sound

state the human range of hearing

20 Hz - 20,000 Hz

state examples of the use of sound waves to explore structure

• echo sound - helps ships detect the ocean floor

• ultrasound - used to look inside the human body and crack detection

• reflection seismology - detects oil and gas underground

• seismic activity - used to investigate earth’s structure

state what properties of a substance allow for detection of hidden structures

• reflection

• absorption

• transmission

• speed of sound in the substance

explain how the properties of a substance allow for detection of hidden structures

• each type of substance will produce different amounts of reflection, absorption and transmission

• each type of substance will also transmit sound at a different speed

• certain structures will reflect a proportion of the sound wave and transmit the rest

• some substances will absorb sound waves with little reflection

• by detecting the amount of sound reflected and the speed of the wave

• the hidden structure can be identified

state the frequency of ultrasound waves in relation to the human hearing range

• ultrasound waves have a higher frequency

• than the upper limit of human hearing

state where ultrasound waves are partially reflected

at the boundary between two different medias

state how to determine how far a boundary that causes ultrasound waves to be partially reflected is

• time taken for the reflections

• to reach the detector

state what ultrasound waves are used for

• industrial imaging

• medical imaging

state what produces seismic waves

earthquakes

state what type of wave p-waves are

• longitudinal

• seismic waves

state how p-waves travel through solids and liquids

at different speeds

state what type of waves s-waves are

• transverse

• seismic waves

state whether s-waves can travel through liquids

no

state what seismic waves provide evidence for

• p-waves and s-waves

• help to explore

• the structure and size

• of earth’s core

explain what echo sounding is used to detect and measure

• detects objects in deep water

• measures water depth

state what echo sounding uses to detect and measure objects in water and water depth

high frequency sound waves

state what the study of seismic waves has provided

• new evidence

• that led to discoveries

• about parts of earth

• that aren’t directly observable

state what electromagnetic waves are

• transverse waves

• that transfer energy

• from the source

• to an absorber

state what electromagnetic waves form

continuous spectrum

state whether electromagnetic waves travel at the same velocity through air and vacuums

yes

state how the electromagnetic spectrum is grouped

by wavelength and frequency

state the electromagnetic spectrum from longest wavelength to shortest wavelength

• radio waves

• microwaves

• infrared

• visible light

• ultraviolet

• x-rays

• gamma rays

state the electromagnetic spectrum from lowest frequency to highest frequency

• radio waves

• microwaves

• infrared

• visible light

• ultraviolet

• x-rays

• gamma rays

state what electromagnetic waves human eyes detect

visible light

describe the energy transfers by microwaves

• water molecules absorb certain wavelengths of microwave radiation

• causing microwave ovens to transfer energy by radiation

• to the thermal store of the food placed inside it

describe the energy transfers by infrared

• all hot objects emit infrared radiation

• these emitted waves can then be absorbed by other objects

• transferring energy to the thermal store of these objects and the surroundings

• by radiation

describe energy transfers from the sun

• the sun emits several types of EM radiation including

• visible light waves which allow living creatures to see

• infrared waves which heat up the earth

• ultraviolet waves which cause suntans and sunburns

• energy is transferred from the sun by radiation

state how the wavelength of EM radiation affects substances

• affects if the substances

• absorbs, transmits, refracts or reflects

• EM waves

describe how EM waves affect the refraction of a substance

• the different velocity the EM waves travel through different substance

• causes differences in the refraction of substances

state when refraction occurs

• when light passes a boundary

• between two transparent mediums

state what happens in refraction

light rays undergo a change in direction

state what the normal is

• hypothetical line

• perpendicular to the surface of the medium

state the change in direction of a light ray from a less dense medium to a denser medium

light ray bends TOWARDS the normal

explain the change in direction of a light ray from a less dense medium to a denser medium

• velocity of light rays DECREASES

• causing the light ray to bend

• towards the normal

• as different parts of the wavefront enter the medium at different times

• causing them to change velocity at different times

state the change in direction of a light ray from a denser medium to a less dense medium

light ray bends AWAY from the normal

explain the change in direction of a light ray from a denser medium to a less dense medium

• velocity of light rays INCREASES

• causing the light ray to bend

• away from the normal

state the change in direction of a light ray when passing along the normal

light ray DOES NOT BEND

state the wave properties that change during refraction

• velocity

• wavelength

state what the different frequencies of visible light account for

different colours of light

state what happens when light refracts

it doesn’t change colour

explain why the refraction of light doesn’t cause a change in wave frequency

• different frequencies of visible light are cause by changes in colour

• when light refracts it doesn’t change colour

• meaning refraction causes the frequency of the visible light wave to remain the SAME

state the method to draw a ray diagram

1. draw a 2D prism on a piece of paper

2. draw a parallel ray on the left of the prism

3. draw the refracted ray at the first surface

4. the ray will bend towards the normal as the prism is denser than air

5. draw the refracted ray at the second surface

6. the ray will bend away from the normal as the air is less dense than the prism

explain how to use wave front diagrams to explain refraction

• when waves hit different mediums

• different parts of the wave enter the medium at different times

• leading to a change in wavespeed

• difference in speed between parts of the wave in the first and second medium causes the wave to bend

• leading to a change in direction

• this refraction is represented in wave front diagrams

state the variables in the investigation of infrared radiation

• independent = colour

• dependent = temperature

• control = same volume of water

state the method of investigating infrared radiation

1. set up four identical flasks painted black, grey, white and silver

2. fill the flasks with hot water, ensuring the measurements start from the same initial temperature

3. note the starting temperature

4. use a stopwatch to measure the temperature every 30 seconds for 10 minutes

analyse the investigation of infrared radiation

• all warm objects emit thermal radiation in the form of infrared waves

• intensity of the emitted radiation depends on

• temperature, surface area and colour of the object

• most of the heat lost from the flasks is due to conduction and convection, which will be the same for each flask

• any difference in heat lost between flasks must be due to infrared radiation

• plot a graph of temperature (y-axis) against time (x-axis) to compare heat loss in each flask

state what produces radio waves

• oscillations

• in electrical circuits

state what absorbed radio waves may create

• alternating current

• at the same frequency

• as the radio wave

state what radio waves can induce

• oscillations

• in an electrical circuit

state what changes in atoms and the nuclei of atoms causes

• the generation of EM waves

• the absorption of EM waves over a wide frequency range

state what gamma rays originate from

• changes

• in the nucleus

• of an atom