Waves Flashcards

Question

How does an ultrasound work?

Answer 1

The time taken for the wave to reflect off the surface of the tissue is measured, so an image is created

Answer 2

Sound waves are produced by vibrating objects and travel as a series of compressions and rarefactions of air particles. Sound waves are longitudinal waves. They can be reflected, refracted or diffracted. Sound waves travel through solids, liquids and gases but they cannot travel through a vacuum.

Answer 3

A musical instrument digital interface, it can produce a wide range of sound

Answer 4

About 343 m/s, in dry air, at 20C. Both humidity and temperature affect the density of the air. The denser the material, the faster sound will travel

Answer 5

1. Work in pairs 2. Start the stop watch when you see the bars/ balloon being hit/popped 3. Stop the stop watch when you hear the sound 4. Record the distance between the clapper and listener 5. Use v = s/t to calculate the speed of the sound Distance must be between 70-100m, using a trundle wheel for measurement.

Answer 6

- very inaccurate due to human error/reaction time - could be improved with more repeats and increased distance between the people

Answer 7

Animals like bats or dolphins use echolocation to detect prey and find each other. Their noises will reflect off of the prey and they can hear the echo, telling them the distance and their location.

Answer 8

It is the range at which a result is right (eg. 309m/s is in the order of magnitude of 343 m/s)

Answer 9

1. Stand 170m away from a cliff and clap once 2. Measure the time for an echo to be heard with a stopwatch It is more accurate as there is a larger distance than the last one (as you double the distance due to there and back). To increase reliability, repeat. Use: Average speed (m/s) = distance (m) / time (s)

Answer 10

1. Use a signal generator, microphones and cathode ray oscilloscope. 2. Make a loud sound near the first microphone (using two blocks): this will trigger the timer. When the sound waves reaches the second microphone it will switch off the timer. 3. The distance between the microphones is recorded (using a metre ruler). 4. Calculate the speed the wave travelled at over this distance using v = s/t Or do the same thing, but instead calculate the difference between the two wave starts in divisions on the oscilloscope (1div = 0.001s usually), so then do 1000/time to find the speed of the wave. This method is more accurate as it eliminates human reaction time. To make more reliable, repeat.

Answer 11

1. Longitudinal sound waves reach microphone 2. The signal is converted to electrical pulses 3. The electrical signal is sent to the oscilloscope 4. The oscilloscope displays a transverse wave on the screen 5. The peaks represent the compressions

Answer 12

1. Set up a speaker with a built-in microphone with another microphone at a distance from it 2. Play a high-pitched sound from the speaker 3. Observe the stationary wave from the speaker and the moving wave from the microphone on the oscilloscope 4. Move the microphone to initially line the waves up together 5. Record this point on a ruler 6. Move the waves up by a wavelength until they line up again 7. Measure that point, and find the difference in distance 8. Use the signal generator to get the frequency (or just use divisions on the oscilloscope) 9. Use the wave equation to find the speed of sound in air This is very accurate Sources of error is human error (where the waves line up), so just use someone facing directly at the wave (90 degree angle), with one perspective Scale isn’t very precise Temperature or humidity

Answer 13

• Light travels in straight lines • Light is given out by luminous objects • We see non-luminous objects because they reflect light. • Light waves can be reflected refracted, reflected and diffracted (means spreading out, but don’t need for know for GCSE) • Light travels faster than sound

Answer 14

Hint: it looks like ripples N/a

Answer 15

The crest/top of a transverse wave. Like bird’s eye view

Answer 16

When a ball is dropped in a glass, the ripples/waves spread out perpendicularly, so the wave energy travels perpendicular

Answer 17

Apparatus: - ray box (standard for light) - plane mirror - pencil - ruler Aim: change the angle of incidence so it equals the angle of reflection 1. Set it up over paper 2. Pre-draw the mirror and normal lines 3. Draw 3 small crosses in the centre of the rays with a sharp pencil and join them up with a ruler

Answer 18

The “normal” is a construction –line perpendicular to the reflecting surface at the point of incidence

Answer 19

reflected. We can draw simple ray diagrams to show reflection. Whenever we draw ray diagrams we must include a normal line. This is a line at 90˚ to the surface.

Answer 20

The law of reflection states that the angle of incidence is always equal to the angle of reflection. i = r

Answer 21

The direction of wave fronts

Answer 22

When a wave goes from one medium to another, the wave speed changes. The more dense a medium, the slower the wave travels. This may cause the wave to change direction. This is called refraction. v = f x λ So, faster wave speed = longer wavelength Slower wave speed = shorter wavelength Frequency is determined by the source so is the same

Answer 23

N/a This is because the entire wave front changes speed at the same time

Answer 24

The wave speed slows down and changes direction as it enters the glass block, which is more optically dense, from the air, which is less optically dense. When leaving the glass block, the wave returns to its normal speed and direction The ray is still parallel, but has been displaced by the more optically dense material

Answer 25

N/a But remember the last and start ray are parallel

Answer 26

As the light moves from one medium to another it may change direction. However, when we see objects, we assume that the light the light has travelled in one direct, straight line. This can cause some strange effects, especially with water and air. That is why fish spearing is very hard, as you have to adjust for the fish being lower down than you think

Answer 27

- the ray of light that travels from the object to the mirror’s surface is called the incident ray - the ray that reflects off the surface of the mirror into the eye is called the reflected ray - the normal is a line drawn at right angles to the reflector - the angle of incidence is between the incident (incoming) ray and the normal - the angle of reflection is between the reflected ray and the normal - the angle of refraction is between the normal and the refracted ray - the emergent ray is the ray that emerges after refraction - the refracted ray is the ray refracted

Answer 28

1. Same size as object 2. Same distance from mirror as object 3. Virtual (cannot be touched) 4. Laterally inverted (left becomes right, right becomes left)

Answer 29

The surface makes a difference the amount of light being reflected. Shiny, smooth surfaces produce clear images. Rough, dark surfaces reflect light in all directions. N/a

Answer 30

Apparatus: - glass block - ray box - pencil/protractor - paper 1. Set up a glass block on a piece of paper, and shine a ray at it using the ray box, at a point 2. Mark the point where the incident and emergent ray meets the glass block, and draw the sides the glass block. Also draw 3 or more crosses on each ray 3. Link them for the refracted ray, then using a protractor, draw the normal 4. Measure the angles of i and r using the normal line and protractor 5. Repeat for a range of different rays and calculate sin(i) and sin(r) Analyse at least 5 angles, from like 10-80 degrees incrementing 10 degrees Precautions: - don’t shine light in eyes - don’t touch ray box bulb - glass

Answer 31

A graph of sin i (the sine of the angle of incidence) against sin r (the sine of the angle of refraction) shows a straight line through the origin, with a 1.5 gradient. This is a directly proportional relationship.

Answer 32

Gradient = change in sin i / change in sin r = rise/run

Answer 33

n = sin(i) / sin(r) where: n = refractive index, i = angle of incidence, r = angle of refraction

Answer 34

The refractive index of a material is a measure of the change in speed of light as it passes from a vacuum (or air as an approx) into the material. It is the ratio of the speeds in the two different mediums, so has no units. The greater the refractive index, the slower the light travels in that material and the more it can bend when it enters the material.

Answer 35

If the wave slows down (i.e. from air to glass/water) then it bends towards the normal. If the wave speeds up (i.e. from glass/water to air) then it bends away from the normal. Learn “TA GAGA” A wave bends… Towards Air->Glass, Away Glass ->Air

Answer 36

The greater the refractive index, the more light bends when it enters the material. N/a

Answer 37

When light travels from one material to another it refracts (bends). However, some light is always reflected. If the light is at a large enough angle from the normal then all the light is reflected back. This is called total internal reflection (TIR).

Answer 38

light is travelling from a dense material to a less dense one, for example from water to air or plastic to air.

Answer 39

The critical angle is the angle that creates an angle of refraction of 90 degrees.

Answer 40

i < c Below the critical angle most light is refracted (some is reflected). i = c At the critical angle, light is directed along the boundary, (with some reflection). The angle of refraction is 90 degrees. i > c Above the critical angle, all the light is reflected back within the more optically dense medium

Answer 41

The critical angle for a material depends on its refractive index. sin(c) = 1 / n Or, rearranged to find n n = 1 / sin(c) You can write it to 2.d.p, but keep exact value on calculators to avoid rounding error.

Answer 42

Periscopes, binoculars, diamonds, optical fibres, endoscopes, rainbows

Answer 43

Shorter, easy to carry around, show you images the right way up due to prisms, brighter image

Answer 44

As astronomers don’t care about which way up the nights sky is

Answer 45

Normal line

Answer 46

- the angle of incident light is greater than the critical angle, and - the light is travelling in the more optically dense of the two materials

Answer 47

1. Light enters the more dense medium and slows down. This causes it to refract 2. The different wavelengths of light refract by different amounts causing the light to disperse creating a spectrum It is travelling in a more dense medium. It hits the surface at an angle of incidence bigger than the critical angle. This means that total internal reflection occurs As it hits the surface at an angle smaller than the critical angle it passes through. It speeds up in the air so refracts again making the dispersion even greater resulting in a rainbow!

Answer 48

• Are transverse waves • Transfer energy from one place to another •Can travel through a vacuum •Travel at the same speed – (the speed of light = 3 × 108 m/s) •Travel as electric and magnetic disturbances through space •Obey the wave equation: – wavespeed = frequency x wavelength • speed slightly decreases when passing through denser objects • can be polarised (meaning their oscillations can be restricted to a specific plane) • they can be reflected, refracted and diffracted

Answer 49

Remember my instructions visible using x-ray glasses. Radio waves Microwaves Infra-red radiation Visible Light Ultra Violet X-rays Gamma rays

Answer 50

Name λ f Radio wave 10^3m 10^4 Hz Microwaves 10^-2m 10^8Hz Infra-red 10^-5m 10^12Hz Visible 0.5x10^-6m 10^15Hz Ultra Violet 10^-8m 10^16Hz X-rays 10^-10m 10^18Hz Gamma 10^-12m 10^20Hz

Answer 51

They transfer energy and information without transferring matter

Answer 52

Radio waves: communication and broadcasting (TV, satellite, Wi-Fi) Microwaves: cooking food (high frequency microwaves penetrate food and area absorbed by water and fat molecules, increasing internal energy and heating), and satellite and mobile comms (as they can pass through atmosphere) Infra-red radiation: heating, night vision equipment, thermal imaging, medical treatment (biopsy and muscle injury as it promotes blood flow), remote controls Visible light: optical fibres and photography Ultra violet: fluorescent lamps, detecting security ink in bank notes, helps production of vitamin D X-rays: observing the internal structure of objects and materials, including for medical application Gamma rays: sterilising food, and medical equipment

Answer 53

With waves, the higher the frequency, the likelier the damage from exposure. Radio waves: little rise in body temperature Microwaves: internal heating of body tissues (causing burns or organ damage), so it is designed with a metal mesh Infrared: skin burns Visible light: looking straight at a light source can damage the retina, so wear sunglasses, and wide-brim hats Ultra violet: damage to eyes (sunglasses absorb UV), damage to skin (sunscreen), damage to surface cells and blindness X-rays: exposure to low radiation (short-term) creates a very low risk of cancer development in years due to radiation (1 in a million) Gamma rays: cancer, mutation (to prevent, use dense shielding material, maximise distance, and reduce time spent near sources)

Answer 54

The body produce more melanin, a dark pigment, to form a protective layer around skin cells, preventing DNA damage

Answer 55

X-ray: good for bones and hard structures, not good for cartilage, muscle or tendon Ultrasound: good for soft structures, ideal for children or repeat patients due to lack of harmful radiation

Answer 56

Microwave: (better) penetrates more layers, targets water molecules to transfer heat by convection, causing better internal heating Infrared: only heats outermost layer, dries out food (absorbed at surface), only better for surface browning

Answer 57

Radio waves: long range, can pass through walls, all directions, limited data capacity Microwaves: high data transmission rate, highly directional, susceptible to rain/interference (water absorption)

Answer 58

a change in the observed frequency and wavelength of a wave when its source is moving relative to an observer.

Answer 59

If the source of a sound is moving away from you, the wavelength increases (decreasing distance between wave fronts), hence the frequency decreases, as waves take longer to reach you and due to the wave equation v=fλ (as wave speed stays constant, which means frequency or wavelength must change). This is why an ambulance getting further away from you seems to have a lower pitch. If the source of the sound is moving towards you, the wavelength decreases (increasing the distance between wave fronts) and frequency increases, as waves take less time to reach you. This is why ambulances have a higher pitch when they are closer to you.

Answer 60

This happens because the wave-fronts get compressed in front of the moving source and spread out behind the moving source.

Answer 61

This also occurs with visible light. Light waves in front of the moving object are compressed. This decreases the wavelength which increases the frequency making the light more blue. Light waves behind the moving object are stretched out. This increases the wavelength which decreases the frequency making the light more red.

Answer 62

When something travels faster than the speed of sound or exceeds the sound barrier, you hear what sounds like an explosion after it passes you. When the object is moving it compresses waves behind it until it is trapped at supersonic speed in a Mach cone, which is why you only hear the boom after. These are strong pressure waves, that can’t escape break windows if strong enough.

Answer 63

Medical imaging of blood clots

Answer 64

It is a biological sonar used by animals (such as bats, dolphins and whales) to navigate and hunt in low-light or dark environments by emitting sound waves (clicks or chirps) and interpreting the returning echoes to identify the objects location, size, distance and texture. Scales are very reflective. N/a

Answer 65

The speed of sound increases with temperature = higher temperature = more kinetic energy in air molecules = faster vibration = more efficient sound wave transfer

Waves Flashcards

(100 cards)