P5.

1 Electromagnetic Radiation Knowledge Organiser

Properties of Waves 18. The peak is the highest point on the

1. Waves may be either transverse or wave and the trough is the lowest
longitudinal. point on the wave.
2. Sound travels in waves.
3. Sound is made when an object causes Observing Waves
air particles to vibrate. 19. The speed of water waves can be
4. A wave is a way of transferring measured using a ripple tank
information or energy.
5. Waves can cause matter to oscillate.
6. Energy moves perpendicular to matter
in transverse waves (e.g. water and
light waves)

7. Energy moves parallel to matter in

longitudinal waves (e.g sound). 20. The speed of a wave on a string can
be measured
21. The velocity of a wave is the speed of
the wave in the direction it is travelling.
22. Velocity of the wave = displacement /
time, S = d/t
23. Velocity of the wave (m/s) =
8. Longitudinal waves show areas of frequency (Hz) x wavelength (m), v = f
compression and rarefaction. xλ
9. Waves can be reflected or refracted.
10. Wave frequency is the number of The Electromagnetic Spectrum
waves that pass each second. 24. Electromagnetic waves are transverse
11. The unit of frequency is hertz (Hz). waves that transfer energy from the
12. Increasing the frequency causes a source of the waves to an absorber.
higher pitch sound. 25. Electromagnetic waves form a
13. Humans can hear a range of 20-20000 continuous spectrum and all types of
Hz. Ultrasound has a frequency higher electromagnetic wave travel at the
than 20000 Hz. same velocity through a vacuum
14. The period is the length of time it takes (space) or air (3x106 m/s)
one second to pass a given point.
15. The wavelength of a wave is the
distance from one point one wave to
the identical point on the next wave,
measured in meters.
16. The amplitude of the wave is the
maximum distance of a point on the
wave from its rest position.
17. Increasing the amplitude increases the
volume.
26. The waves that form the
electromagnetic spectrum are
P5.1 Electromagnetic Radiation Knowledge Organiser

grouped in terms of their wavelength waves being generated or absorbed

and their frequency. Going from long over a wide frequency range.
to short wavelength (or from low to Gamma rays originate from changes
high frequency) the groups are: radio, in the nucleus of an atom.
microwave, infrared, visible light (red 38. Ultraviolet waves, X-rays and gamma
to violet), ultraviolet, X-rays and rays can have hazardous effects on
gamma rays. human body tissue. The effects
27. (HT Only) Different substances may depend on the type of radiation and
absorb, transmit, refract or reflect the size of the dose. Radiation dose (in
electromagnetic waves in ways that sieverts) is a measure of the risk of
vary with wavelength. harm resulting from an exposure of the
28. (HT Only) Some effects, for example body to the radiation.
refraction, are due to the difference in 39. Ultraviolet waves can cause skin to
velocity of the waves in different age prematurely and increase the risk
substances. of skin cancer. X-rays and gamma rays
29. (HT Only) Wave front diagrams can be are ionising radiation that can cause
used to explain refraction as they show the mutation of genes and cancer.
the change of speed that happens 40. Electromagnetic waves have many
when a wave travels from one practical applications. For example:
medium to another. - radio waves - television and radio
- microwaves - satellite
Uses of Electromagnetic Spectrum communications, cooking food
30. Our eyes only detect visible light and - infrared - electrical heaters, cooking
so detect a limited range of food, infrared cameras
electromagnetic waves. - visible light - fibre optic
31. The visible spectrum is made of the communications
colours red, orange, yellow, green, - ultraviolet - energy efficient lamps,
blue, indigo and violet sun tanning
32. Red light has the longest wavelength - X-rays and gamma rays - medical
(lowest frequency) and violet has the imaging and treatments
shortest wavelength (highest
frequency)
33. (HT Only) Radio waves can be
produced by oscillations in electrical
circuits.
34. (HT Only) 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.
35. (HT Only) High frequency microwaves 41. Each type of electromagnetic wave is
are easily absorbed by food suitable for its different practical
molecules, increasing their internal application because of its wavelength
energy and frequency.
36. (HT Only) Microwaves easily pass
through the atmosphere so are used Reflection and Refraction (Physics Only)
between stations on Earth and 42. Reflection from a smooth surface in a
satellites in orbit single direction is called specular
37. Changes in atoms and the nuclei of reflection. Reflection from a rough
atoms can result in electromagnetic
P5.1 Electromagnetic Radiation Knowledge Organiser

surface causes scattering: this is called

diffuse reflection.
43. Ray diagrams can be used to show
the refraction of a wave at the
boundary between two different
media.
44. Refraction is the change of direction
of a wave when it moves from one
medium to another because it
changes speed
45. A wave slows down if it moves from a 55. Ray diagrams are used to show the
less dense to a more dense medium, formation of images by convex and
causing it to bend towards the normal concave lenses.
46. When light reaches a different 56. A convex lens is thicker in the middle
medium, some light can be reflected that at the edges and rays of light
and some is refracted. converge through a convex lens to
meet at the principal focus
57. The image produced by a convex lens
can be either real or virtual.
58. A virtual image is one that appears to
come from behind the lens
59. A concave lens is thinner in the middle
than at the edges and rays of light
diverge through a concave lens
47. The incident ray is the incoming ray. 60. The image produced by a concave
48. The normal line is an imaginary line lens is always virtual.
from which angles are measured. It is 61. Convex lenses are found in cameras,
drawn from the point of incidence at human eyes, projectors and
right angles to the surface. magnifying glasses
49. Angle of incidence is the angle 62. Concave lenses are found in peep
between the normal and the holes
incidence ray.
Ray Diagrams (Physics Only)
Visible Light and Lenses (Physics Only) 63. In ray diagrams a convex lens is
50. Objects that transmit light are either represented with two outward facing
transparent or translucent. arrows and a concave lens is
51. Translucent objects allow some light to represented with two inward facing
pass through, transparent objects arrows
allow most light to pass through 64. The images formed by a lens can be:
52. Objects that do not transmit light are upright or inverted, magnified or
opaque and shadows can form diminished, real or virtual
behind them 65. The magnification produced by a lens
53. A lens forms an image by refracting can be calculated using the equation:
light. In a convex lens, parallel rays of magnification = image height/object
light are brought to a focus at the height
principal focus. 66. Magnification is a ratio and so has no
54. The distance from the lens to the units.
principal focus is called the focal 67. Image height and object height
length. should both be measured in either mm
or cm.
P5.1 Electromagnetic Radiation Knowledge Organiser

Colour (Physics Only) in wavelength. This effect is called red-

68. Each colour within the visible light shift.
spectrum has its own narrow band of 77. The observed red-shift provides
wavelength and frequency. evidence that space itself (the
universe) is expanding and supports
the Big Bang theory.
78. Scientists use observations to arrive at
theories such as the Big Bang theory
79. The Big Bang theory suggests that the
universe began from a very small
region that was extremely hot and
dense.
80. Since 1998 onwards, observations of
supernovae suggest that distant
galaxies are receding ever faster.
81. Red-shift of light from galaxies that are
69. Waves can be absorbed at the
receding is evidence for the Big Bang
boundary between two different
model
materials
82. The change of each galaxy’s speed
70. When waves are absorbed by a
with distance is evidence of an
surface, the energy of the wave is
expanding universe
transferred to the particles in the
83. Scientists do not yet understand why
surface, increasing their internal
the Universe is expanding increasingly
energy
quickly but have suggested the idea
71. Colour filters work by absorbing certain
of dark energy, which is thought
wavelengths (and colour) and
84. to account for over 2/3 of the Universe
transmitting other wavelengths (and
85. Scientists have also discovered that
colour).
galaxies rotate too quickly for the mass
72. The colour of an opaque object is
of their stars, leading scientists to think
determined by which wavelengths of
that there is mass that is invisible to
light are more strongly reflected.
current scientific instruments, but has
Wavelengths that are not reflected
gravity that affects nearby objects.
are absorbed. If all wavelengths are
Scientists call this mass dark matter
reflected equally the object appears
86. Only 5% of the Universe is made of
white. If all wavelengths are absorbed
matter that we currently understand
the objects appears black.

The Big Bang Theory and Red Shift RPA: Infrared Radiation
87. An infrared thermometer can be used
(Physics Only)
to measure emission of infrared
73. Light from a star does not contain all
radiation
the wavelengths of the EM spectrum
88. White, silver, shiny surfaces are poor
as elements in the star can absorb
absorbers/ emitters of infrared
some of the wavelengths
radiation as they reflect all visible light
74. This produces dark lines when the
wavelengths
emission spectrum is analysed
89. Radiators are often painted white to
75. Different elements produce different
release infrared radiation steadily
emission spectra
90. Dark, matte surfaces are good
76. There is an observed increase in the
emitters of infrared radiation
wavelength of light from most distant
91. A Leslie cube can be used to
galaxies. The further away the
investigate emission of infrared
galaxies, the faster they are moving
radiation
and the bigger the observed increase
P5.1 Electromagnetic Radiation Knowledge Organiser

92. A Leslie cube is a metal cube with four when the body absorbs radiation
different types of surface, and can be faster than it emits radiation.
filled with hot water
Earth and Radiation (Physics Only)
99. The temperature of the Earth depends
on many factors including: the rates of
absorption and emission of radiation,
reflection of radiation into space, and
the concentration of greenhouse
gases in its atmosphere
100. The temperature of a body is
related to the balance between
incoming radiation absorbed and
radiation emitted, using everyday
examples to illustrate this balance,
and the example of the factors which
determine the temperature of the
Earth.
101. The Earth absorbs infrared
radiation and visible light, increasing its
Black Bodies and Radiation (Physics internal energy
Only) 102. The Earth transfers energy to the
93. All bodies (objects), no matter what atmosphere via conduction and
temperature, emit and absorb infrared convection
radiation. The hotter the body, the 103. The Earth emits infrared
more infrared radiation it radiates in a radiation, some of which is absorbed
given time. by greenhouse gases
94. There are no known objects that are 104. These greenhouse gases then
perfect at absorbing or emitting all emit infrared radiation in all directions,
radiation, but objects that come close including back to Earth, where it is
are called black bodies then reabsorbed
95. A perfect black body is an object that 105. The greenhouse effect is
absorbs all of the radiation incident on caused by natural greenhouse gases
it. A black body does not reflect or which stabilise the surface
transmit any radiation. Since a good temperature of the Earth, allowing it to
absorber is also a good emitter, a support life
perfect black body would be the best
possible emitter.
96. A perfect black body is a theoretical
object
97. Stars are considered to be black
bodies because they are good
emitters (and therefore absorbers) of
most wavelengths in the EM spectrum.
Planets and black holes are also nearly
perfect black bodies
98. A body at constant temperature is
absorbing radiation at the same rate
as it is emitting radiation. The
temperature of a body increases 106. However, human activities
(including burning fossil fuels and
P5.1 Electromagnetic Radiation Knowledge Organiser

deforestation) are increasing the

concentration of greenhouse gases in
the atmosphere, causing more
infrared radiation to be absorbed by
the gases and causing an enhanced
greenhouse effect"