Seneca P6 Flashcards
(124 cards)
1
Q
Waves
A
Waves transfer energy from one place to another without transferring matter. Wave motion (the movement of waves) can be shown by the vibrations of a spring or by water waves.
2
Q
Springs - transverse waves
A
Hold one end of a horizontal spring in a fixed position and move the other end of the spring up and down.
We can observe a wave moving from the end we are holding towards the fixed end of the spring.
3
Q
Water
A
When a wave travels along the surface of the water, a cork floating on the surface of the water will only move up and down as the wave passes.
4
Q
What do waves transfer?
A
Energy
5
Q
What is the formula for wave speed
A
v =f x λ
We can calculate speed by multiplying the frequency of the wave by its wavelength. The unit for wave speed is meters per second
6
Q
Spring Vibrations Experiment
A
. Hold one end of a horizontal spring in a fixed position
. Move the end of the spring up and down
. Observe a wave moving from towards the fixed end of the spring
7
Q
What is the formula for frequency of a wave
A
f = n / t
frequency = oscillations / time
8
Q
Measuring waves
A
Two important measurements for waves are amplitude and wavelength. Both are measured in meters
9
Q
Amplitude
A
The amplitude of a wave is the largest distance that a point on the wave moves from its rest position. For example, the distance from the rest position of a wave to the top of a wave’s peak
10
Q
Wavelength
A
The wavelength is the distance between two adjacent wave fronts. For transverse waves, this is the distance between two peaks of adjacent waves.
11
Q
Transverse waves
A
A transverse wave causes the particles in the medium (the substance that the wave travels through) to vibrate at right angles to the direction of the wave’s motion. A cork in water and the coils of a spring are examples of this. They move up and down as the wave passes.
12
Q
Longitudinal waves
A
A longitudinal wave causes the medium’s particles to vibrate in the same direction as the wave’s motion. Examples of longitudinal waves are sound waves and pushing a spring in and out.
13
Q
Wave fronts
A
Water waves can be set up in a Ripple Tank, where a rod at one end of a tank of water creates a series of ripples.
A bright light shone through the water onto a sheet of paper shows the ripples on the water very clearly as a series of parallel lines travelling along with constant speed.
These parallel lines are the peaks of the ripples on the water. We call them wave fronts.
14
Q
What is the distance between two wavefronts?
A
Wavelength
15
Q
Wave speed equation
A
v=f x λ
speed or velocity = frequency x wavelength
16
Q
Waves at a boundary
A
When waves travel from one medium to another, their speed and wavelength change but their frequency stays the same.
17
Q
Speed and wavelength change
A
The speed of a wave changes when it travels from one medium to another.
The wavelength of a wave also changes when it travels from one medium to another.
The speed and the wavelength are directly proportional:
If the speed doubles, the wavelength doubles.
If the speed halves, the wavelength halves.
The frequency of the wave does not change because the source is producing the same number of oscillations (vibrations) per second.
18
Q
Transmission
A
Waves carry on travelling through a new material.
This often leads to refraction.
19
Q
Reflection
A
Reflection happens when a wave hits a flat surface (plane) and bounces off.
20
Q
Absorption
A
When waves meet some materials, the energy is absorbed by the material.
For example, when light falls on a matt black surface, most of the energy is absorbed.
21
Q
Refraction
A
A wave’s speed can change when moving from one medium to another.
If the wave crosses to the new medium at an angle (not 90 degrees), the change in the wave’s speed will cause the direction of the wave’s motion to change and the wave will appear to bend.
This is called refraction.
22
Q
Angle of incidence
A
The angle of incidence is the angle between the incident (incoming) light ray and the normal.
The normal is a line at 90 degrees to the plane.
23
Q
Angle of reflection
A
The angle of reflection is the angle between the reflected light ray and the normal.
24
Q
Law of reflection
A
The law of reflection states that the angle of incidence = the angle of reflection.
25
What is the normal?
A line 90 degrees to the plane
26
When is light refracted
Light is refracted when it travels from one medium to another and changes speed.
27
Less optically dense materials
If light speeds up on entering a new medium, this medium is “less optically dense”.
The light is refracted further from the normal - the angle of refraction is larger than the angle of incidence.
28
Optically dense materials
If light slows down as it enters a new medium, this medium is “more optically dense”.
When light enters a more optically dense medium, it is refracted closer to the normal.
This means that the angle of refraction is smaller than the angle of incidence.
29
Internal reflection
Light speeds up when entering a less optically dense medium. When this happens, some light is refracted and some light is reflected. This is internal reflection.
30
Total internal reflection
If the angle of incidence exceeds the critical angle, then all the light will be reflected. This is called total internal reflection.
31
What is the name of the angle above which all light is reflected?
Critical angle
32
If the angle of incidence is the same as the critical angle
If the angle of incidence is the same as the critical angle, the light will travel along the boundary of the 2 mediums.
33
What are sound waves
Sound waves are longitudinal waves. They can travel through solids by causing vibrations in the solid.
34
How is sound produced
Sound is produced by the vibration of particles in a medium (the substance that waves travel through).
The vibrations mean that sound waves travel in a series of compressions (where the medium is squashed together) and rarefactions (where the medium is stretched apart).
35
Vibrations cause sound waves to travel through a medium in a series of:
Compressions and Rarefractions
36
What is the range of frequencies we can hear
Our ears are sensitive to (can hear) a range of frequencies between 20Hz and 20,000 Hz.
37
Sound and Age
The range of frequencies that we can hear changes with age.
Elderly people tend to become less sensitive to sounds with a higher frequency.
38
Ultrasound
Ultrasound has a frequency above 20,000Hz. Humans cannot hear sounds with frequencies this high, but other animals can.
Dog whistles have frequencies above 20,000Hz, which is why humans cannot hear them.
Ultrasound is also used by doctors to perform scans of a developing foetus.
39
Our ears are designed to detect vibrations and transfer the information to our brain via the -------- nerve.
auditory
40
Sound travel
Sound needs to travel through a medium. The more rigid the medium is, the higher the speed of the sound wave through the medium. The more compressible the medium is, the slower the speed of the sound wave through the medium.
41
Sound and gas
Gases are readily compressible (easy to squash), so the speed of sound in a gas is very slow.
42
Sound and solids
Solids are significantly more rigid than liquids and gases and are very hard to compress.
Therefore, the speed of sound in solids is much higher than in liquids or gases.
43
Sound and liquids
Liquids are more rigid and less compressible than gases, so the speed of sound in liquids is much higher than in gases.
44
Measuring the Speed of Sound - Experiment
Two people stand a measured distance from a tall vertical wall. This distance should ideally be about 100m.
The first person bangs two wooden blocks together to make a sharp sound and repeats this every time the echo is heard.
Starting counting from zero, the second person uses a stopwatch (timer) to measure the time taken for a number of claps – 50 or 100.
In the time between two successive claps, the sound travels to the wall and back.
The speed of sound can be calculated from the following relationship:
speed of sound = distance to wall × 2 × number of claps (N) ÷ time taken for N claps.
45
Because sound is a wave, it can be:
. Transmitted
. Refracted
. Reflected
. Absorbed
46
An ____ is an example of the reflection of sound.
echo
47
Ultrasound at a boundary
When ultrasound waves meet a boundary between two different materials, some are reflected. We can work out how far away a boundary is based on how long it takes for reflections to reach a detector. We can use ultrasound waves for both medical and industrial imaging.
48
Ultrasound training dogs
Ultrasound has a frequency above 20,000Hz. Humans cannot hear sounds with frequencies this high, but other animals can.
Dog whistles have frequencies above 20,000Hz. This is why humans cannot hear them.
49
Ultrasound in water
We can use echo sounding to detect objects in deep water and also to measure water depth.
We send an ultrasound pulse into the water. When this pulse hits any surface, it is reflected back.
We can work out the distance travelled by the sound wave by recording the time between us sending the pulse and detecting the reflection.
50
Ultrasound in medicine
Doctors use ultrasound to perform scans of a developing foetus.
Ultrasound waves can pass through the body.
Whenever they reach a boundary between two different materials, some will be reflected. We can detect the reflected waves.
A computer processes the timing and distribution of these waves. The computer uses these to produce a video image of the foetus.
51
Ultrasound in industry
We can use ultrasound to find flaws in objects or materials (e.g. pipes or wood).
When ultrasound waves enter a material, they will normally be reflected by the far side of the material.
If there is a flaw (e.g. a crack), the waves will be reflected sooner. This tells us that there is a problem.
52
Seismic waves are waves which travel through the Earth. Earthquakes produce two types of seismic waves:
. P-waves (primary)
. S-waves (secondary)
53
P-waves (primary)
These are longitudinal, seismic waves.
P-waves travel at different speeds through solids and liquids.
54
S-waves (secondary)
These are transverse, seismic waves.
S-waves cannot travel through liquids (only through solids).
55
Uses of seismic waves
Seismic waves cannot travel through all parts of the earth because the earth is made up of different materials.
Scientists have used this principle to work out the different materials that the earth is made up of.
By detecting seismic waves from Earthquakes, scientists have worked out that the Earth has a solid core surrounded by a liquid outer core.
A mantle of changing density surrounds the Earth’s core. This mantle causes the refraction of the seismic waves.
56
Wave energy
Electromagnetic waves transfer energy from the source of the wave to an absorber of the wave.
Gamma rays also carry the most amount of energy than any other wave in the electromagnetic spectrum.
Wave energy increases with frequency.
Wave energy decreases with wavelength.
57
Wavelength vs frequency
As you move from gamma rays to radio waves, the wavelengths increase and the frequencies decrease.
Gamma rays have the shortest wavelength and the highest frequency.
Radio waves have the longest wavelength and the lowest frequency.
58
What are the seven electromagnetic waves from highest to lowest frequency
gamma, X-ray, ultraviolet (UV), visible, infrared, microwave, and radio waves.
59
Uses of gamma rays
Gamma rays are used for medical imaging and therapy, astronomy, sterilization and food preservation.
60
Risks of gamma rays
Gamma rays are extremely penetrating and damaging to living tissues and cells.
61
Explanation of gamma rays
Gamma rays carry the most energy. We can use gamma rays to destroy bacteria and tumours.
62
X-Ray safety precaution
Due to the dangerous nature of X-rays, exposure to X-rays should always be kept to a minimum.
People working with X-ray equipment should always shield themselves to prevent exposure to X-rays.
These people will place materials (metals like lead) between themselves and the X-rays.
63
Uses of X-Rays
Low-energy X-rays are used for medical and industrial imaging.
High-energy X-rays are used to treat cancer.
X-rays are also used for security purposes to detect weapons in airports (and other places).
64
X-ray explanation
X-rays penetrate soft materials (like body tissue).
Bones are dense materials that absorb X-rays. We can use X-rays to build a shaded image of bones and body tissue.
65
X-Ray risks
X-rays are highly ionising (can damage body cells), even in low doses.
66
UV uses
Ultraviolet light is used in medical and forensic photography, air purification, disinfection and medical therapy.
Ultraviolet light can also be used to detect fake bank notes.
67
UV explanation
In lamps, UV photons excite (gives energy to) atoms. The atoms then release visible light.
In sun tanning, UV excites (gives energy to) skin cells. The skin cells then change color.
68
Risks of UV
Exposure to too much ultraviolet light can cause skin burns, skin cancer and cataract formations in the eye.
69
Risks of infared
Infra-red radiation can cause serious skin burns if emitted from high-intensity sources.
70
Infrared explanation
The frequency is high enough to excite particles in food. This increases their temperature.
Infra-red cameras can detect a range of frequencies. These frequencies can be shown in different colours to depict images.
71
Infrared uses
Infra-red radiation is used in TV controls.
Infra-red can also be used for security purposes, such as in intruder alarms by detecting body heat.
72
Microwave risks
Because humans are largely made up of water, exposure to microwaves could have a harmful effect.
73
Microwave explanation
Microwaves have a high enough frequency to penetrate the Earth’s atmosphere and to reach satellites.
Microwaves travel in straight lines through the atmosphere. This makes them good for transmitting (sending) signals.
74
Microwave uses
Microwaves are used for the purpose of satellite communications (transmitting signals between stations on Earth and satellites).
Microwaves are also used to transmit signal from a nearby phone mast (transmitter) to a mobile phone.
Microwaves are absorbed by water, heating up the water in the process. This makes microwaves useful for cooking food because food contains lots of water.
75
Microwave safety
We should always reduce any exposure to microwaves.
As with X-rays, always have some sort of shielding between the source of microwaves and living tissue.
An example of this is the protective shielding on microwave ovens.
76
Radio wave risks
At high intensities, radio waves can cause internal heating of living tissue with potentially harmful effects.
77
Radio waves explanation
Because radio waves have long wavelengths, they can be transmitted (sent) around the Earth’s surface and around buildings without interference.
78
Radio wave uses
Radio waves are used for radio and TV communications.
79
How do changes in atoms produce electromagnetic waves
Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range.
Gamma rays originate from changes in the nucleus of an atom.
80
How do electrical circuits produce electromagnetic waves
Oscillations (repeating variations) in electrical circuits can produce radio waves.
When radio waves are absorbed, they can create an alternating current with the same frequency as the radio wave itself.
This means that radio waves can lead to oscillations in an electrical circuit.
81
Visible light explanation
We use visible light in optical fibres because it can be totally internally reflected.
This means that we can transmit signals (information) along optical fibres without the signals (information) getting lost.
82
Visible light spectrum
Traditionally, we say that there are seven colours of light in the spectrum.
Red, Orange, Yellow, Green, Blue, Indigo and Violet.
83
Visible light uses
We use visible light to see the world around us and in fibre optics.
84
Visible light and opaque items
Opaque objects either reflect or absorb all light that hits them.
No light passes through.
85
Visible light and transparent items
Transparent objects also transmit light without scattering the rays.
We can clearly see objects on the other side of transparent objects.
86
Visible light and translucent items
Translucent objects transmit light but the rays are scattered.
We cannot see objects clearly through translucent objects.
87
What are the two ways light can be reflected from a surface
. Diffuse reflection
. Specular reflection
88
Diffuse reflection
Diffuse reflection happens when light is reflected by a rough surface.
This is because the light is scattered.
89
Specular reflection
Specular reflection happens when light is reflected by a smooth surface in a single direction.
90
Color filters
Colour filters absorb certain wavelengths (colours) and transmit other wavelengths (colours).
Objects appear as different colours based on how the colours of white light are absorbed and reflected.
91
Color of opaque objects
When an opaque object looks like it has a particular colour, it is reflecting light of that particular wavelength (colour) and absorbing all other wavelengths.
If all wavelengths are reflected equally, the opaque object looks white.
If all wavelengths are absorbed, the object looks black.
92
Red filter
If a blue book was looked at through a red filter, the book would look black.
This is because the red filter will only allow red light to pass through.
It will absorb all other colours of light.
93
Blue filter
If a blue book was looked at through a blue filter, it would still look blue.
This is because the reflected blue light can pass through the filter.
94
What are the two types of lenses
. Concave lenses
. Convex lenses
95
Convex lens
A convex lens is curved on both sides and is wider at the middle than at the edges.
The principal focus of a convex lens is the place where all the rays hitting the lens parallel to the axis meet.
The distance from the lens to the principal focus is called the focal length.
A convex lens is also called a converging lens.
96
Concave lens
A concave lens is wider at the edges than in the middle.
When parallel rays of light enter a concave lens, they disperse (spread out).
If you trace back along the paths of the dispersed rays, they will look like they came from the principal focus that is behind the lens.
A concave lens is also called a diverging lens.
97
What images to convex lens produce
Convex lenses produce images that are either real or virtual.
A real image appears on the other side of the lens to the object. We can project real images onto a screen.
A virtual image appears on the same side of the object. We cannot project virtual images onto a screen.
98
What images to concave lens produce
Concave lenses only produce virtual images.
A virtual image appears on the same side of the object. We cannot project virtual images onto a screen.
99
Magnification
We can use this equation to calculate the magnification a lens produces:
magnification = image height ÷ object height
Magnification is a ratio. It has no units.
We should measure the image’s height and object’s height in either mm or cm.
100
Magnification equation
magnification=image height÷object height
101
What are the units of magnification?
It is a ratio, so no units
102
reminder
ray diagrams
103
What is the name of the horizontal line that goes straight through the middle of the lens?
Principle axis
104
Symbols for ray diagrams
(reminder)
reminder
105
What type of image can we project on to a screen?
Real
106
Electromagnetic wave
Infra-red radiation is an electromagnetic wave (it is part of the electromagnetic spectrum).
We cannot see it but we do feel it as heat.
107
The sun
The infra-red radiation emitted by the Sun transmits thermal (heat) energy to the Earth.
Infra-red radiation does not need a medium, so can still travel through space.
108
White surfaces
White surfaces are good reflectors of infra-red radiation.
White surfaces are poor emitters and absorbers of infra-red radiation.
109
Perfect black body
A perfect black body is an object that absorbs all of the radiation incident on it.
A black body does not reflect or transmit any radiation.
Since a good absorber is also a good emitter, a perfect black body would be the best possible emitter.
110
Shiny surfaces
Shiny surfaces of a colour are poorer absorbers of radiation than dull surfaces of the same colour.
Shiny surfaces are poorer emitters and better reflectors than dull surfaces of the same colour.
111
Black surfaces
Black surfaces are good emitters, good absorbers and poor reflectors.
112
high surface temperature
Bodies with a higher surface temperature will emit radiation faster.
113
High surface area
Bodies with a large surface area will emit radiation faster.
114
How can we detect infra-red radiation
As heat
115
Properties of infra-red
. Does not need a medium
. Is an electromagnetic wave
. Transfers thermal energy
116
Changing temperature
An object will always transmit (send) heat from a hotter area to a colder area.
Radiators work based on this principle.
This means that when an object’s internal temperature is higher than the temperature of the environment around it, the rate of emission will be higher than if the object were in a warmer environment.
117
Constant temperature
A body at constant temperature absorbs radiation at the same rate that it emits radiation.
118
Temperature and black bodies
All bodies (objects) emit radiation. The temperature of a body (object) is linked to the intensity (rate) and wavelength of the emitted radiation. Black bodies are perfect absorbers and emitters of radiation - they never reflect or transmit radiation.
119
Which of these is a property of a perfect black body?
All radiation is absorbed
120
What does the temperature of a body (object) depend on
The temperature of a body (object) depends on the rate of absorption of radiation and the rate of emission of radiation
121
The rates of absorption and emission can be affected by:
. Surface area
. Internal temperature
. External temperature
122
What is the process behind the greenhouse effect
The sun emits short wavelength infrared radiation that enters the atmosphere and travels towards the Earth’s surface.
The Earth absorbs some of this radiation, but long wavelength radiation is reflected back into the atmosphere.
Greenhouse gases (e.g. carbon dioxide, methane, water vapour) can't absorb the frequency of radiation emitted by the Sun. But they can absorb the longer wavelength reflected radiation.
The gases then re-radiate this energy in all directions, including back towards Earth.
This increases the temperature at the Earth’s surface.
123
Heat absorbed (entering the Earth)
340 Watts per square metre of solar energy falls on the Earth.
29% is reflected back into space - primarily by clouds, but also by other bright surfaces and the atmosphere itself.
About 23% of incoming energy is absorbed in the atmosphere by atmospheric gases, dust, and other particles.
The remaining 48% is absorbed at the surface.
124
Heat emitted (leaving the earth)
Absorbed sunlight is balanced by heat radiated from Earth’s surface and atmosphere.
Most heat escapes from areas just north and south of the equator, where the surface is warm, but there are few clouds.
Along the equator, persistent clouds prevent heat from escaping.
Likewise, the cold poles radiate little heat.
