Waves

Question 1

Describe what is Meant by a Transverse Wave

Answer 1

-In a transverse wave, the oscillations are perpendicular to the direction of energy transfer.

-Not all transverse waves require a medium to travel. For example light is a transverse wave and this travels through a vacuum.

-For example, all electromagnetic waves, ripples and waves in water.

Question 2

Describe what is Meant by a Longitudinal Wave

Answer 2

-In a longitudinal wave, the oscillations are parallel to the direction of energy transfer.

-All longitudinal waves always need a medium to travel through.

-For example, sound waves in air, ultrasound and shockwaves, some seismic waves.

Question 3

Describe what is Meant by Amplitude

Answer 3

The amplitude of a wave is the maximum displacement of a point on the wave from the equilibrium.

Question 4

Describe what is Meant by Wavelength

Answer 4

The wavelength is the distance between the same point on two adjacent waves.

Question 5

Describe what is Meant by Frequency

Answer 5

-Frequency is the number of complete waves passing a certain point (oscillations) per second.

-Frequency is measured in Hz. 1 Hz is 1 wave per second.

Question 6

Describe what is Meant by Period

Answer 6

-The period is the amount of time it takes for a full cycle of the wave.

-Period = 1 ÷ Frequency

Question 7

Describe what is Meant by Compression and Rarefraction

Answer 7

-Compression is where the particles are closer than the equilibrium.

-Rarefraction is where the particles are further apart than the equilibrium.

Question 8

State the Wave Equation

Answer 8

Wave Speed (m/s) = Frequency (HZ) x Wavelength (m)

v = f x λ

Question 9

Describe a Method for Measuring the Speed of Sound in Air

Answer 9

-Person A holds a pair of symbols and Person B holds a timer. They are separated by a distance of 500m.

-Person B starts timing when they see Person A crash the symbols together. They stop timing when they hear the sound of the symbols.

-To calculate the speed of the sound waves, we divide the distance between persons A and B by the time.

Question 10

Describe the Sources of Inaccuracy When Measuring the Speed of Sound in Air

Answer 10

-Every person has a different reaction time. If one person recorded the time between seeing the cymbals clash and hearing the sound, the result would depend on that one person’s reaction time.

-This means that the result would be unlikely to be accurate. A person with a longer reaction time would produce a less accurate result than a person with a shorter reaction time.

-The time interval between seeing the cymbals clash and hearing the sound is very short. If the time interval is very short, this makes it very difficult to press the timer at the correct times.

Question 11

Describe how to Reduce the Inaccuracy When When Measuring the Speed of Sound in Air

Answer 11

-Every person has a different reaction time. A large number of people should be used, each with their own timer. Then a
mean value should be taken of their results. This would reduce the effect of different reaction times.

-The time interval between seeing the cymbals clash and hearing the sound is very short. This problem can be reduced by increasing the distance between the person holding the cymbals and the observers.

-This would increase the time interval between seeing the cymbals clash and hearing the sound, making it easier to press the timer at the correct times.

Question 12

Describe a Method to Measure the Speed, Frequency and Wavelength of Waves in a Ripple Tank

Answer 12

-Set up the ripple tank with about 5 cm depth of water. Adjust the height of the wooden rod so that it just touches the surface of the water.

-Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.

-Measure the length of a number of waves then divide by the number of waves to record wavelength.

-It may be more practical to take a photograph of the card with the ruler and take measurements from the still picture.

-Count the number of waves passing a point in ten seconds then divide by ten to record frequency. Calculate the speed of the waves using: wave speed = frequency × wavelength.

Question 13

Explain how to Determine Wave Speed in a Ripple tank Without Measuring Wavelength

Answer 13

-Measure the distance travelled by a wave using a metre rule.

-Measure the time taken for the wave to travel the measured distance with a stopwatch.

-Divide the distance by the time.

-The most accurate way to do this is to record the ripple tank with a mobile phone and then play it back at a slower speed.

Question 14

Describe a Method to Measure the Speed, Frequency and Wavelength of Waves on a String

Answer 14

-Attach a string to a vibration generator and use a 200g hanging mass and pulley to pull the string taut. Connect the vibration generator to a signal generator.

-Switch on the vibration generator and adjust the frequency on the signal generator until there is a clear wave on the string.

-Measure the length of as many half wavelengths (loops) as possible, then divide by the number of half wavelengths (loops). This is half the wavelength, doubling this gives the wavelength.

-The frequency is the frequency of the power supply. Calculate the speed of the waves using: wave speed = frequency × wavelength.

Question 15

Give Another Method to Change the Tautness of the String and the Standing Wave When Measuring Waves in a Solid

Answer 15

-A student could change the tautness of the string by changing the mass hanging from the pulley. A greater mass would increase the tautness of the string.

-As well as changing the frequency, we can also adjust the standing wave on the string by adjusting the position of the wooden bridge.

-As we move the wooden bridge closer to or further from the vibration generator, the standing wave will change.

Question 16

Describe what Happens When a Wave Hits a Boundary

Answer 16

-The wave can be transmitted through the material. This means it carries on travelling through the material and con often lead to refraction.

-In some cases, the energy of the wave can be absorbed. If this happens then the wave may not pass through the material at all.

-The wave could simply be reflected off the surface of the material. These means the energy goes back to the original medium.

-Which of these happens depends on the wavelength of the wave.

Question 17

Describe what is Meant by Specular Reflection

Answer 17

Specular reflection happens on smooth surfaces when parallel light rays hit the surface and reflect as parallel light rays. This forms images.

Question 18

Describe what is Meant by Diffuse Reflection

Answer 18

-Diffuse reflection happens on rough surfaces when parallel light rays hist the surface and reflect as scattered light rays. No images are formed.

-This happens because the normal is different foreach incoming ray which means that the angle of incidence is different.

-When light is reflected by a rough surface, the surface appears matte and there is no clear reflection of objects.

Question 19

Describe the Method for the Reflection Practical

Answer 19

-Take a piece of paper and draw a straight line across it. Place an object so on one of its sides lines up with this line.

-Shine a ray of light at the object’s surface and trace the incoming and reflected light beams.

-Draw the normal line at the point where the ray hits the object. Use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table.

-Repeat this experiment using blocks made of different materials.

Question 20

Describe the Refraction of Light

Answer 20

-In general, the higher the density of a material, the slower a wave travels through it.

-If a wave crosses a boundary and slows down, it will bend towards the normal. If it crosses into a material and speeds up, it will bend away from the normal.

-The wavelength of a wave changes when it is refracted but the frequency stays the same.

-If the wave is travelling along the normal, it will change speed but it will not refract.

Question 21

Explain why Waves Refract at a Boundary

Answer 21

-When a wave moves form one medium to another, its velocity may change.

-If the wave arrived at the interface and an angle one side of the wave will arrive before the other.

-This causes the one side of the wave to change velocity before the other side so the wave will change direction.

Question 22

Describe a Wave Front Diagram for a Wave that Speeds Up When Entering a Material

Answer 22

-When the first wavefront starts to move out of the glass, those parts of the wavefront speed up.

-Those parts of the wavefront now get further
apart.

-The wavelength of the waves increases.

-The wave changes direction away from the
normal.

Question 23

Describe a Wave Front Diagram for a Wave that Slows Down When Entering a Material

Answer 23

-When the first wavefront starts to move into the glass, those parts of the wavefront slow down.

-Those parts of the wavefront now get closer
together.

-The wavelength of the waves decreases.

-The wave changes direction towards the
normal.

Question 24

Describe a Wave Front Diagram for a Wave Entering a Material Along the Normal

Answer 24

-When wavefronts travel along the normal, the whole wavefront enters the glass at the same time.

-This means that each part of the wavefront slows down together and the wave does not change direction.

Question 25

Describe a Method for the Refraction Practical

Answer 25

-Place a glass block on a piece of paper. Draw around the glass block. Use the ray box to shine a ray of light through the glass block. -Mark the ray of light entering the glass block. Mark the ray of light emerging from the glass block. Join the points to show the path of the complete ray through the block. -Draw a normal line at 90 degrees to the surface. Use a protractor to measure the angle of incidence. Use a protractor to measure the angle of refraction. -Use a ray box to shine a ray of light at a range of different angles (of incidence). Increase the angle of incidence in 10 degree intervals from an angle of incidence of 10 degrees to an angle of incidence of 70 degrees.

Question 26

Explain how to Investigate the Effect of a Material on Refraction

Answer 26

-Instead of changing the angle of incidence, repeat the experiment using blocks made of different materials. -However, keep the angle of incidence the same throughout.

Question 27

Explain why the Lights Need to be Turned Off During the Reflection and Refraction Practical

Answer 27

-In this experiment, we are using a narrow ray of light and observing how this is reflected or refracted by a glass block. -The ray of light produced by most ray boxes can be quite faint. We turn the lights off because the ray is easier to see in a darkened room.

Question 28

Explain why Using a Wider Ray Would Give Less Accurate Results than Using a Narrower Ray.

Answer 28

It is harder to judge where the centre of a wider ray is, causing a larger uncertainty in the measurements.

Question 29

Describe what is Meant by Optical Density

Answer 29

-The optical density of a material is a measure of how quickly light can travel through it. -The higher the optical density, the slower light waves travel through it.

Question 30

Describe the Properties of Sound Waves

Answer 30

-Sound waves are longitudinal waves. They are caused by vibrating particles, These vibrations are passed through the surrounding medium as a series of compressions and rarefractions. -Sound travels faster in solids than in liquids and faster in liquids than in gases. Sound does not travel through a vacuum as there are no particle to move or vibrate.

Question 31

Explain why the Speed of Sound is a Solid is Greater than in Air

Answer 31

-In solids, the particles are closer together than the particles in air. -This means that when sound waves pass through solids, the vibrations can pass more easily between the particles than when sound waves pass through air. -This means that the speed of sound in a solid is greater than the speed of sound in air.

Question 32

Explain why Human Hearing has a Range of Between 20 and 20,000 Hz

Answer 32

-The frequency range of human hearing is between 20 Hz and 20 000 Hz. -One of the reasons for this is that any frequencies outside of that range may not cause the eardrum to vibrate. -Sound waves can only cause solids to vibrate over a limited range of frequencies.

Question 33

Explain how the Ear Works

Answer 33

-Sound waves that reach the ear cause the ear drum to vibrate. These vibrations make the ossicles move like levers. -This movement is transferred to liquid which moves hairs in the cochlea. -The cochlea turns these vibrations into pressure waves. Pressure waves are transferred into electrical signals which are sent to the brain. -The brain processes the electrical signal and a sound is heard.

Question 34

Explain how Ultrasound Works

Answer 34

-When a wave passes from one medium to another, some of the wave is reflected off the boundary between the two media and some is transmitted. -This means that a pulse of ultrasound can be pointed at an object and wherever there are boundaries between one substance and another, some of the ultrasound gets reflected back. -The time it takes for the reflections to reach a detector can be used to measure how far away the boundary is.

Question 35

Describe the Use of Ultrasound in Pre-Natal Scans

Answer 35

-Waves will pass through liquids such as blood but will bounce back off solids such as bone. -The timing and distribution of these echoes are processed by a computer. -This creates a map of the uterus, with bright white dots representing higher density areas. -Doctors can also ultrasound to detect blood flow.

Question 36

Describe the Use of Ultrasound in Industry

Answer 36

-Ultrasound can also be used to find flaws in objects such as pipes or materials such as wood or metal. -Ultrasound waves entering a material will usually be reflected by the far side of the material. -If there is a flaw such as a crack inside the object, the wave will be reflected sooner.

Question 37

Describe the Advantages of Ultrasound

Answer 37

-Does not require surgery. -Does not produce ionising radiation -Ultrasound machines are often small and portable so can be used almost anywhere.

Question 38

Compare Ultrasound and X-Rays

Answer 38

Ultrasound: -Mechanical and longitudinal -Non-ionising -Reflected off tissue boundaries X-rays: -Electromagnetic and transverse -Ionising -Passes through soft tissues and absorbed by bone

Question 39

Describe the Uses of Seismic Waves

Answer 39

-Scientists have worked out the internal structure of the Earth using earthquakes. -When an earthquake takes place, there is a sudden movement between the Earth's tectonic plates. -Seismic waves now carry energy away from the earthquake. These waves pass through the Earth and are then detected by seismometers in different countries. -The pattern of the seismic waves gives us information about the Earth's interior.

Question 40

Describe the Properties of S-Waves and P-Waves

Answer 40

-P-waves are longitudinal and can pass through both solids and liquids. -S waves are transverse and can only pass through solids. This means that S waves cannot pass through the outer core (which is a liquid). -S waves travel more slowly than P waves.

Question 41

State the Electromagnetic Spectrum

Answer 41

-Long wavelength, low frequency and energy Radio waves Micro waves Infrared radiation Visible light Ultraviolet X-rays Gamma rays -Short wavelength, high frequency and energy

Question 42

Describe the Properties of All EM Waves

Answer 42

-All EM waves are transverse and transfer energy from a source to an absorber. -All EM waves travel at the same speed through a vacuum (3 x 10^8 m/s). -They form a continuous spectrum.

Question 43

Describe how Radio Waves are Emitted and Absorbed by an Electrical Circuit

Answer 43

-Radio waves are emitted when electrons oscillate in an electrical circuit. -Radio waves can be absorbed by an electrical circuit. When the radio waves are absorbed, they cause electrons in the circuit to oscillate. -This produces an alternating current (AC) with the same frequency as the radio waves.

Question 44

Describe the Uses of Radio Waves

Answer 44

-Radio waves are useful for transmitting radio and TV signals because they can travel long distances without being absorbed. -Short wave radio can also be received at long distances from the transmitter because they are reflected off the ionosphere. -Long wave radio can be transmitted long distances because the long wavelengths diffract around the curved surface of the Earth.

Question 45

Describe the Uses of Microwaves for Satellites

Answer 45

-Microwaves are used to communicate with satellites in space. This is because, unlike radio waves, microwaves are not reflected off the ionosphere. -This means that they can pass straight through the ionosphere to satellites out in space. -For satellites, the signal from a transmitter is transmitted into space where it is picked up by the satellite receiver dish orbiting above the Earth in a different direction. -The satellite transmits the signal back to Earth where it is received by a satellite dish on the ground

Question 46

Describe the Uses of Microwaves in Microwave Ovens

Answer 46

-In microwave ovens, the microwaves are absorbed by water molecules. -The microwaves penetrate a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food causing the water to heat up. -The water molecules then transfer this energy to the rest of the molecules in the food by heating- which quickly cooks the food.

Question 47

Describe the Uses of Infrared to Monitor Temperature

Answer 47

-Infrared cameras can be used to detect infrared radiation and monitor temperature. -The camera detects the infrared and turns it into an electrical signal which is displayed on a screen as a picture. The hotter an object is, the brighter it appears. -Infrared detectors can be used to spot where heat is escaping from buildings. -These can then be upgraded with better insulation to reduce energy loss and improve the energy efficiency of the building.

Question 48

Describe the Uses of Infrared to Increase Temperature

Answer 48

-Absorbing infrared causes objects to get hotter. Food can be cooked using infrared radiation- the temperature of the food increases when it absorbs infrared. -Wrapping food in aluminium foil can prevent it from burning. That is because infrared radiation is not absorbed by shiny metallic surfaces (it will be reflected). -Electric heaters contain a long piece of wire that heats up when a current flows through it. The wire then emits lots of infrared. The emitted infrared is absorbed by objects and air in the room. -Energy is transferred by the infrared waves to the thermal energy stores of the objects causing their temperatures to increase.

Question 49

Describe the Uses of Visible Light

Answer 49

-Visible light is used in communication. -Rapid pulses of light can be sent down optical fibres. These are very thin strands of glass. -They work because the light rays are bounced back and forth until they reach the end of the fibre. -Visible light has a short wavelength so it can carry a lot of information. -Infrared is also used in optical fibres.

Question 50

Describe the Uses of Ultraviolet

Answer 50

-Ultraviolet is used in fluorescent lights. These lights generate UV which is absorbed and re-emitted as visible light by a layer of phosphor inside the lightbulb. -They are very energy efficient compared to normal light bulbs and stay relatively cool. -Security pens can be used to mark property. Under UV the ink will glow but is invisible otherwise. -UV is also emitted by the Sun and gives people a tan. When its not sunny, people go to tanning salons where UV lamps are used to give artificial tans.

Question 51

Describe the Uses of X-Rays

Answer 51

-X rays are absorbed by bones. This means that we can use X rays to visualise bones in the human body. -When we take an X ray, the X rays pass straight through normal tissue but not bones. The X rays can then be detected on an X ray detector, allowing us to visualise the bones. -X-rays are also used to treat cancer. This is because high doses will kill living cells. They are carefully directed towards cancer cells to avoid killing too many healthy cells.

Question 52

Describe the Uses of Gamma Rays

Answer 52

-Gamma radiation can be used as a medical tracer. This is where gamma emitting source is injected into the patient and its progress is followed around the body. -Gamma is good for this because it can pass out of through the body to be detected. -Gamma rays are also used to treat cancer. This is because high doses will kill living cells. They are carefully directed towards cancer cells to avoid killing too many healthy cells.

Question 53

Describe the Dangers of Long Wavelength Electromagnetic Waves

Answer 53

-Radio waves and microwaves can be hazardous because they penetrate people's bodies and can heat the internal parts of the body. -Infrared radiation can be hazardous because is is absorbed by skin. It can damage, burn or kill skin cells because it heats up the cells.

Question 54

Describe the Dangers of Short Wavelength Electromagnetic Waves

Answer 54

-UV radiation damages surface cells which can lead to sunburn and cause skin to age prematurely. Some more serious effects are blindness and increased risk of skin cancer. -X-rays and gamma rays are types of ionising radiation. This means they carry enough energy to knock electrons off of atoms. This can cause gene mutation or cell destruction and cancer.

Question 55

Compare the Effects of a Concave and Convex Lens

Answer 55

-A convex lens bulges outwards. It causes rays of light parallel to the axis to be brought together at the principal focus (converge). -A concave lens caves inwards. It causes parallel rays of light to spread out (diverge). -An axis of a lens is a line that passes through the middle of the lens.

Question 56

Compare the Principal Focus of a Concave and Convex Lens

Answer 56

-The principal focus of a convex lens is where rays hitting the lens parallel to the axis all meet. -The principal focus of a concave lens is the point where rays hitting the lens parallel to the axis appear to all come from.

Question 57

Describe the Rules for Refraction in a Convex Lens

Answer 57

-An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side. -An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis. -An incident ray passing through the centre of the lens carries on in the same direction.

Question 58

Describe the Rules for Refraction in a Concave Lens

Answer 58

-An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus. -An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel the axis. -An incident ray passing through the centre of the lens carries on in the same direction.

Question 59

Describe what is Meant by a Real and Virtual Image

Answer 59

-A real image is where the light from an object appears to form an image on a 'screen'. -A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place.

Question 60

Describe how to Draw a Ray Diagram for an Image Through a Convex Lens

Answer 60

-Pick a point on the top of the object. Draw a ray going from the object to the lens parallel to the axis of the lens. -Draw another ray from the top of the object going through the middle of the lens. -The incident ray that is parallel to the axis is refracted through the principal focus on the other side of the lens. Draw a refracted ray passing through the principal focus. -The ray passing through the middle of the lens does not bend. Mark where the rays meet. This is the top of the image.

Question 61

Draw a Ray Diagram for an Image Through a Concave Lens

Answer 61

-Pick a point on the top of the object. Draw a ray going from the object to the lens parallel to the axis of the lens. -Draw another ray from the top of the object going through the middle of the lens. -The incident ray that is parallel is refracted so it appears to have come from the principal focus. Draw a ray from the principal focus. make it dotted before the lens. -The ray passing through the middle of the lens does not bend. Mark where the refracted rays meet. This is the top of the image.

Question 62

Explain why Concave lenses Produce a Virtual Image

Answer 62

Concave lenses produce a virtual image because the light rays are not focussed at the principal focus.

Question 63

Describe the Colour Spectrum

Answer 63

-Each colour of light has a narrow band of wavelengths and frequencies. -The three primary colours are: red, green and blue. -White objects reflect all of the wavelengths of visible light equally. -Black objects absorb all wavelengths of visible light.

Question 64

Explain What is Meant by Transparent, Opaque and Translucent

Answer 64

-Transparent objects transmit light through them without scattering the light rays. This means that we can see clearly through transparent objects -Translucent objects transmit light through them but the light rays are scattered. This means that we cannot see clearly through the object. -Opaque objects completely block the transmission of light so we cannot see any light passing through an opaque object.

Question 65

Describe how Colour Filters Work

Answer 65

-Colour filters are used to filter out different wavelengths of light so that only certain colours are transmitted and the rest are absorbed. -A primary colour filter only transmits that colour. If the object was a different colour to the filter, the object would appear black. All of the light reflected by the object will be absorbed by the filter. -Filters that are not primary colours let through both the wavelengths of light for that colour and the wavelengths of the primary colours that can be added together to make that colour.

Question 66

Describe the Emission and Absorption of Infrared radiation

Answer 66

-Infrared radiation is a type of electromagnetic wave. It can be emitted and absorbed by all objects. The higher the temperature, the more IR an object will emit. -It is used in TV remotes, thermal imaging cameras and space exploration. -All bodies, no matter their temperature emit and absorb IR. If the object is at a constant temperature it emits IR at the same rate as it absorbs it.

Question 67

Describe what is Meant by Black Body Radiation

Answer 67

-A perfect black body is something which absorbs all infrared radiation that hits it. It doesn't reflect or transmit any radiation. It is also the best possible emitter of radiation. -Objects at a constant temperature will emit a range of wave lengths of radiation. Some wavelengths will have a different colour. -As you heat up an object, you can change the wavelengths of radiation emitted. This can change the objects colour.

Question 68

Describe a Method to Measure how Much Infrared is Emitted from Different Surfaces

Answer 68

-Place a Leslie cube on a heat-resistant mat. Fill it, almost to the top, with boiling water and replace the lid. -Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water. -Use the infrared detector to measure the intensity of infrared radiation emitted from each surface. -Make sure that the detector is the same distance from each surface for each reading.

Question 69

Explain why an Infrared Detector is better than a Thermometer for the Infrared Practical

Answer 69

-The difference in the amount of infrared emitted by the different surfaces may be very small. -While this difference may be detectable with an infrared detector, it might not be detectable using a thermometer.

Question 70

Give a Risk Assessment for the Infrared Practical

Answer 70

Hazard- Boiling water Risk- Scalds Control Measure- Pour water slowly, using a funnel if necessary. Do not move the Leslie cube until it has cooled.

Question 71

Describe a Method to Measure how Much Infrared is Absorbed by Different Surfaces

Answer 71

-First, use vaseline to attach a drawing pin to a sheet of metal. -One side of the metal is painted either shiny silver, shiny black, matt black or matt white. -Place the sheets of metal next to an infrared heater. -The temperature of the metal sheets increases as the surfaces absorb infrared radiation. -Time how long it takes for the vaseline to melt and the drawing pins to fall off the metal sheets.

Question 72

Explain how Radiation Affects the Earth's Temperature in the Long Term

Answer 72

-The Sun emits short wavelength radiation. This radiation travels through space to the Earth. Some of the radiation is reflected back into space from the atmosphere. -The remaining radiation passes through the atmosphere and can be absorbed by the surface of the Earth, causing the temperature of the Earth to increase. -The surface of the Earth now emits infrared radiation. However, some of the infrared is absorbed by greenhouse gases. -As human activity increases the levels of greenhouse gases, more heat energy is trapped in the atmosphere and less is radiated into space. This increases the temperature of the atmosphere.

Question 73

Explain how Radiation Affects the Earth's Temperature in the Short Term

Answer 73

-During the day, lots of radiation is transferred to the earth from the Sun and absorbed. This causes an increase in local temperature. -At night, less radiation is being absorbed than is being emitted, causing a decrease in the local temperature,

Question 74

Explain why Cloudy Nights Tend to be Warmer than Clear Nights

Answer 74

-At night time, the surface of the Earth which is in darkness now emits more infrared radiation than it absorbs. -On cloudless nights, most of this infrared radiation passes through the atmosphere into space. -However, on cloudy nights, the infrared radiation emitted from the surface of the Earth reflects off the clouds back to Earth. This means that cloudy nights are usually warmer than clear nights.