4.6 Waves

Question 1

Transverse vs longitudinal

Answer 1

Transverse waves have oscillations perpendicular to the direction in which the waves transfer energy

Longitudinal waves have oscillations that a parallel to the direction in which the waves transfer energy.
- longitudinal have areas of compression and rarefaction

Question 2

Amplitude

Answer 2

The maximum displacement of a point on a wave away from its in disturbed position

Question 3

Wavelength

Answer 3

The distance from a point on one wave to the equivalent point on the adjacent wave

Question 4

Frequency (of a wave)

Answer 4

The number of waves passing a point each second

Question 5

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

Answer 5

Two blocks of wood, or other items that make a loud, sharp sound when struck together
A stopwatch
A friend to help with the experiment
A tape measure
Instructions:

two people stand a distance of 100m apart, which is measured using a trundle wheel
one person has two wooden blocks, which they bang together above their head
the second person has a stopwatch which they start when they see the first person banging the blocks together and stops when they hear the sound
this is then repeated several times and an average value is taken for the time
the speed of sound can then be calculated using the equation speed = distance/time

OR USE oscilloscope
two microphones are connectied to an oscilloscope and placed 5m apart using tape measure
make loud clap at first microphone
oscilloscope used to determine the time at which the clap reaches each microphone and the time difference between them
so calculate speed

Question 6

PH: RP8 waves in water

Answer 6

1. Fill the baby ripple tank with water
2. Turn on the strobe light and adjust the frequency of waves
3. Place a ruler next to the screen of the baby ripple tank and take a photo of it
4. Measure wavelength from the photo and record it
5. Count the number of waves that passes a certain point in the baby ripple tank in 10 seconds. Calculate the frequency from this by dividing the number of waves counted by 10
6. Calculate wave speed using equation v = fλ
7. Repeat experiment 5 times and find an mean speed discarding anomalies

Question 7

PH: RP8: waves in a solid

Answer 7

Equipment:
Signal generator
Vibration generator
masses on a mass holder
Length of a string

Method:
1. Set up the apparatus: connect the frequency generator and the vibrator. Attach the string on top of the vibration generator, and pass over the pulley attached at the end of the bench and held fairly taut with the mass holder with masses hanging from the end of the string.
2. Measure the length of string between the vibration generator and the pulley
3. Turn on the signal generator—this will produce vibrations in the string
4. Increase the frequency of the vibration from zero until you can see a wave pattern in the string, with one complete wave on the string
5. Record the frequency of the signal generator in the first row of the results table
6. Continue to increase the frequency until you see a second wave pattern, as shown in the diagram below, with two complete waves
7. Record the frequency on the signal generator in the second row of the results table
8. Continue this process to find the frequencies which form 3 and 4 complete waves.

Question 8

Investigating the speed of ripples on a water surface

Answer 8

1. Pour water into a tray, and measure the length of the tray—this is the distance the wave will travel
2. Measure the time it takes for one of the wave crests to travel to the far end of the tray
3. Use the time taken and the length of the tray to calculate the wave speed

fill a tank
two people stand a few metres apart using a tape measure to measure the distance
one person disturbs the water surface to create a ripple and starts the stop watch
then stop the stop watch when the ripple gets to the second person
repeat 10 times and average

Question 9

Reflection and refraction of waves

Answer 9

Reflection: happens in mirrors when light waves ‘bounce’. The law of reflection: angle of i = angle of reflection

A wave hits a boundary between two media and does not pass through, but instead stays in the original medium

Refraction: happens when waves travel between two mediums of different densities. The waves can speed up or slow down so they bend

When light travels along the normal it will slow down upon entering the block and speed up when it leaves it.
When light travels at an angle it will bend and slow down upon entering the block and bend and speed up again after leaving.

Question 10

Reflection of waves

Answer 10

When a wave hit is a barrier it reflects
The angle of incidence is equal to the angle of reflection
The speed, frequency and wavelength of the wave do not change

Question 11

Refraction of waves: when water waves enter shallow water from deep water

Answer 11

The speed of the wave decreases
The frequency of the wave doesn’t change—this is because the same number of waves enter the shallow water per second as leave the deep water
So the distance between the peaks of the wave, the wavelength, gets smaller

Question 12

Refraction of waves: when waves hit the shallow water at any angle other than 90

Answer 12

Direction of the wave changes
This is because the part of the wave that hits the shallow water first slows down
The waves bend towards the normal
When a wave changes speed and direction we say that it refracts

Question 13

PH: RP9 apparatus

Answer 13

A light source—ray box with a slit and lens to focus the light
Two rectangular transparent blocks of different materials—Perspex and glass
A 12V power supply
30 cm ruler and protractor
A3 plain paper

Question 14

PH: RP9 method

Answer 14

1. Set up the ray box so that it will produce a narrow ray of light. Be careful as the ray box will get hot, turn off when not in use
2. Place a ruler in the centre of the A3 paper and draw a vertical straight line
3. Using a protractor draw a a second straight line at right angles to the first, label this ‘N’ for the normal
4. Place the Perspex block on the paper and draw around
5. Using the ray box direct a ray of light at the point where the block meets the normal, the ray box needs to be at an angle.
6. Using a pencil, mark the path of the light rays with crosses. Make sure you mark all three rays—incident ray, reflected ray and refracted ray
7. Once completed label this side of paper Perspex and repeat the steps for the glass block on the other side
8. Once you have incident, reflected and refracted light rays marked for both Perspex and glass blocks turn the lights on and using a ruler draw straight lines through the crosses to show the pathways.
9. Label the rays you have marked with either, incident ray, reflected ray or refracted ray.
10. Using your protractor measure the angles of; the angle of incidence, the angle of reflection and the angle of refraction. Record your results in a table

Question 15

Sound waves

Answer 15

Sound waves can travel through solids causing vibrations in the solid
Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound. The conversion of sound waves to vibrations of solids works over a limited frequency range

the more molecules that are present, the faster the wave can transfew energy so sound waves travel fastest in solids, and slowest in gases

Human hearing: 20 Hz - 20 kHz

Question 16

Describe with examples processes which convert wave disturbances between sound waves and vibrations in solids

Answer 16

Wave disturbances are any action that cause something to sound/vibrate
When something vibrates, the particles vibrate then hit the air particles which then like a domino result in the air particle layer above to vibrate
The air particles continue to vibrate until they reach the nomes im your ear where they vibrate to process the sound
When you put your head on the surface that vibrates it is louder bc it doesnt have to travel through the air

Question 17

Ultrasound waves

Answer 17

Frequency higher than the upper limit of hearing for humans
Partially reflected when they meet a boundary between two different media
The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is—this allows ultrasound waves to be used for both medical and industrial imaging

Question 18

Seismic waves

Answer 18

Produced by earthquakes
P-waves:
longitudinal
travel through the earth and are refracted when they pass through a medium
cause the ground to move up and down
Pass through solids and liquids
They go faster through more dense material

S-waves:
Transverse
Cause the ground to move left and right
Only pass through solids
Slower than p waves
Go faster through more dense material

Study of seismic waves provided new evidence that led to discoveries about parts of the earth are not directly obtainable

Question 19

Electromagnetic waves

Answer 19

Transverse waves
Transfer energy from the source of the waves to an absorber
Form a continuous spectrum
Travel at the same velocity through a vacuum or air
RMIVUXG
Long wavelength
Radio
Microwave
Infrared
Visible
Ultraviolet
X ray
Gamma
High frequency

Question 20

Radio waves

Answer 20

Produced by oscillations in electrical circuits
When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit

Used for COMMUNICATIONS
Tv broadcasting
Radio broadcasting

Question 21

Microwaves

Answer 21

Used for communications—satellite communications, mobile phones

Microwaves with a wavelength of 3 cm are absorbed by water molecules
Water molecules in food absorb the microwaves, they gain energy and heat up the food
Microwaves penetrate to a depth of about 1 cm into food—larger pieces of food rely on conduction to transfer heat further into the food
Can pass through plastic

Dangers:
Exposure to microwaves with a wavelength of 12 cm lead to burning—can heat water molecules in human

Question 22

Infrared

Answer 22

Uses: remote controls, cooking, heating, IR cameras for tracking criminals

Dangers:
Can cause fires to occur

Question 23

Visible light

Answer 23

Uses:
Seeing things, fibre optic communications

Dangers:
Can blind you

Question 24

UV radiation

Answer 24

Uses:
energy efficient lamdps, Security marking, sunbeds

Dangers:
Can cause skin cancer

Question 25

X rays

Answer 25

Uses: Looking at broken bones/medical imaging Dangers: Ionising/can cause cancer

Question 26

Gamma

Answer 26

Uses: medical imaging, Preserving fruit, killing cancer cells Dangers: Ionising/can kill you/can cause cancer

Question 27

PH: RP10 apparatus

Answer 27

A four sided Leslie’s cube An infrared detector A kettle A heatproof mat

Question 28

Heat transfer—colour of objects

Answer 28

Reflecting radiation: Dark matt objects are poor reflectors of radiation Light shiny objects are good absorbers of radiation Absorbing radiation: Dark matt objects= good Light shiny = poor Emitting: Dark matt emits > light shiny

Question 29

PH: RP10 method

Answer 29

1. Setup the apparatus. Place the Leslie cube on top of a heatproof mat 2. Fill the Leslie’s cube with hot water 3. Using the infrared detector measure the temperature on each surface and therefore the infrared radiation. Make sure the detector is the same distance from each distance 4.record data in table

Question 30

Lenses

Answer 30

The image produced by a convex lens can be either real or virtual. The image produced by a concave lens is always virtual.

Question 31

transparent/translucent objects

Answer 31

transmit light

Question 32

Colour of an opaque object

Answer 32

Light is either absorbed or reflected by an opaque object An opaque object will not transmit light A red object will reflect red light, a red object appears red in red light A red object absorbs blue and green light. It will appear black in blue and green light

Question 33

Colours of light

Answer 33

Red + blue = magenta Red+ green = yellow Blue + green = cyan

Question 34

Types of reflection

Answer 34

Reflection from a smooth surface in a singular direction = specular reflection Reflection from a rough surface causes scattering—called diffuse reflection

Question 35

Black body radiation

Answer 35

A perfect black body absorbs all of the radiation that hits it It does not reflect or transmit any of the radiation that hits it A black body is the best possible emitter of radiation. The radiation emitted is called black body radiation

Question 36

body at constant temperature

Answer 36

A body at constant temperature is absorbing radiation at the same rate as it is emitting radiation The temperature of a body increases when the body absorbs radiation faster than it emits radiation

Question 37

all bodies:

Answer 37

emit radiation the intensity and wavelength distribution of any emission depends on the temperature of the body

Question 38

refraction of sound

Answer 38

from denser medium to less dense medium the wavelength of sound waves decreases, the frequency stays the same, and speed decreases from less dense to denser medium wavelengths increases, frequency stays the same, velocity increases

Question 39

temperature of the earth

Answer 39

Temperature of the earth depends on many factors including: the rates of absorption and emission of radiation, reflection of radiation into space