Pure Physics SA2 Overall Revision Notes
General Physics: Chapter 1
Measurement
Physical Quantities Derived quantities (combining suitable base quantities) E.g. Velocity
Base quantity Name of SI unit Symbol Measurement of Length
Very short Micrometer 0.01mm
Length Metre M
(diameter of small Screw (0.001cm)
Mass Kilogram Kg
wire) Gauge
Time Second S
Short (diameter of Vernier 0.01cm
Electric current Ampere A coin) Calipers
Thermodynamic Kelvin K Medium (Length of Metre Rule 0.1cm
temperature pendulum)
Luminous intensity Candela Cd Long (Length of Measuring 1cm
Amount of substance Mole mol vehicles) tape
Vernier Calipers: Total the values of the main scale and vernier scale readings to obtain
the correct reading. Remember to take note of zero error.
Micrometer Screw Gauge: Total the values of the main scale (1mm) and circular scale
readings (0.01mm) to obtain the correct reading. Take note of zero error.
Measurement of Time: Time can be measured with a
pendulum, clock or stopwatch.
1.) The time taken for 1 complete oscillation is called the
period.
2.) The number of complete oscillations per second is
called the frequency.
3.) The period increases with the length of the pendulum.
2009 Pure Physics SA2 Overall Revision Notes
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Pure Physics SA2 Overall Revision Notes
General Physics: Chapter 2
Kinematics
Types of Quantities Scalar Quantities are fully described by a magnitude only. Distance (m)
Vector Quantities are quantities described by a magnitude and direction.
Displacement: The distance measured along a straight line in a stated direction with respect to the
original point (vector).
Velocity: Rate of change of displacement Displacement (m)
Velocity 
Time Taken (m/s)
Acceleration: Rate of change of velocity Final Velocity  Initial Velocity
Note: Negative Acceleration = Retardation
Acceleration 
Time Taken (m/s)
Displacement – Time Graphs (xt Graphs) Velocity – Time Graphs (vt Graphs)
3.) Used to show displacement over time. 1.) Used to show velocity over time.
4.) Horizontal line: Body at rest. 2.) Such a graph can be used to find:
5.) Straight line with positive gradient: Uniform a. Velocity
Velocity. b. Acceleration: Gradient
6.) Straight line with negative gradient: Uniform c. Distance travelled: Area under the
velocity in the opposite direction. graph.
7.) Curve: Non – uniform velocity.
8.) The gradient of the tangent of this graph gives the
instantaneous velocity of the object.
Acceleration of Free – Fall
2. The acceleration of free-fall near the surface of the Earth is constant and is approximately 10m/s2. It is
derived from the gravitational force felt by objects near the Earth surface and independent of the mass of any
object.
3. Speed of a free-falling body (experiencing no other forces other than gravity) increases by 10m/s every
second or when the body is thrown up, it decreases by 10m/s every second.
4. The higher the speed of an object, the greater the air resistance. 2009 Pure Physics SA2 Overall Revision Notes
5. Terminal Velocity: When an object is moving at constant velocity, acceleration is 0.
6. As an object falls, it picks up speed, increasing air resistance. Eventually, air resistance becomes large enough
to balance the force of gravity where the acceleration of the object is 0, reaching constant velocity.
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Pure Physics SA2 Overall Revision Notes
General Physics: Chapter 3
Forces
Force SI unit: Newton (N) Is a push or a pull. Balanced / Unbalanced Forces
When forces are balanced,
there is no resultant force,
thus no change will occur to
Effects of Forces
on Motion
Newton’s 3 the object
When forces are unbalanced,
Law of Motion
there is a resultant force,
thus object will move towards
the direction with greater
force
Law of Inertia F = ma
Every action has an equal and
opposite reaction
How reluctant an object Resultant Force acting Forces always occur in
is to change. The greater on an object = Product pairs
the mass the more of mass and acceleration Action / reaction forces
reluctant it is. of object. act on different bodies.
An object at rest will
remain at rest and an
object at motion will Friction
remain at a constant
speed with an absence of 1. It is the net force that slows down moving objects.
a resultant force. 2. Acts in the opposite direction of motion of object.
Static Friction: Related Factors affecting the amount Advantages: Walking / Brakes /
to objects which are not of friction: object to remain slanted
moving. Amount of force
applied = amount of 1. Material / texture in Disadvantages: Reduction in
friction. contact efficiency of machinery / energy
Moving Friction: Applied 2. Proportional to force wasted as heat.
force does not affect pressing surface
friction. It can be 3. Independent on area of Methods to reduce friction:
affected by surface / contact. Lubricants, ball / roller bearings,
sudden mass change moving parts made smoother.
2009 Pure Physics SA2 Overall Revision Notes
Terminal Velocity
1. The greater the velocity of an object, the higher the air resistance.
2. Definition: The constant maximum velocity reached by a body falling through the atmosphere under the
attraction of gravity.
3. When an object reaches terminal velocity, the force of gravity and air resistance are balanced, the object falls
at a constant speed and doesn’t accelerate.
4. Factors affected: Size, surface area, weight and nature of medium where object is flying.
5. NOTE: If an object is falling through a vacuum, there would be no air resistance, thus acceleration is due to
gravity alone.
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Pure Physics SA2 Overall Revision Notes
General Physics: Chapter 4
Mass, Weight, Density
Mass Weight Density
Definition Mass is the quantity of matter Weight is the attractive force exerted Density of a substance is defined as its
contained in an object. on an object due to gravity. mass per unit volume.
3 3
SI unit Kilogram (kg) Newton (N) kg/m or g/cm
Equation W  mg
W: Weight of object (N)
m: Mass of object (kg)
g: Gravitational Acceleration in
m/s2
Pure Physics SA2 Overall Revision Notes
General Physics: Chapter 5
Turning Effects of Forces (Moments)
Chapter 5.1: Definitions
1. The moment of a force is the turning effect of a force, or the
ability of the force to make something turn.
2. Moment of a force (M) about a point O is the product of the
force (F) and the
perpendicular distance (D) from the point to the line of
action of the force.
3. SI unit: Newton (N)
4. Moments can be clockwise or anticlockwise. 5. The turning effect of a force depends on:
a. Location of applied force
b. Perpendicular distance between the point of
application of the force and the pivot.
2009 Pure Physics SA2 Overall Revision Notes
Chapter 5.2: Principle of Moments
The principle of moments state that:
When a body is in equilibrium, the sum of clockwise
moments about the balanced point is equal to the sum
of anticlockwise moments about the same point
(pivot).
Total clockwise moment = Total anticlockwise moment.
6. When the clockwise moment is not equal to the
anticlockwise moment, there is a resultant moment. The
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object will rotate in the direction of resultant moment.
7. Therefore, if there is no resultant moment, the object is
balanced!
Chapter 5.3: Centre of Gravity (c.g.)
8. Definition: The centre of gravity (CG) of a body is an
imaginary point where the whole weight of the body
seems to act in any orientation.
a. The CG of a regular object is at the centre.
b. The CG of an irregular object is determined using a
plumb line.
9. If a body is hanging freely at rest, its centre of gravity is
always vertically below the pivot, thus the plumb line
method works. It can only be used for flat, irregular objects.
Chapter 5.4: Stability
10. Stability is a measure of the body’s ability to maintain its
original position.
11. There are 3 types of stability:
Stability Type Effect Explanation
Stable Object will return into Weight will generate an anticlockwise moment by bringing the cone back to
Equilibrium original position after slight its original position (done by the restoring moment).
disturbance These types of objects usually have low CG and big/heavier bases.
Unstable Object will topple/fall after The weight of the cone will generate a clockwise moment outside the base
Equilibrium slight disturbance area of the cone, thus there is a resultant moment and the object will fall.
Neutral Object remains in new The centre of gravity neither rises nor falls, it remains at the same level. The
Equilibrium position after slight lines of action of the 2 forces always concide and there is no moment
disturbance provided by weight to turn the cone.
12. Ways to improve stability of an object:
a. Lowering the CG (A lower CG will allow the line of action to act within the base area of an object)
b. Area of its base should be as wide as possible (allow line of action to act within base area)
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Pure Physics SA2 Overall Revision Notes
General Physics: Chapter 6
Energy, Work, Power
Work Energy Power
Definition Work done on an object is when Energy is the capacity to do work. Power is defined as the rate of doing
a constant force is applied on There are many different types of work (Rate of energy transfer /
the object producing a distance energy like translational, rotational and conversion)
moving in the direction of the vibrational kinetic energy.
force.
SI unit Joule (J) Joule (J) Watt (W)
Definition One joule of work is done when One joule of work is done when an One watt is produced when 1 joule of
of SI unit a force of one Newton moves object with 1kg moves at 1m/s. work is done for 1 second.
through a distance of one metre
in the direction of the force.
Equation W  FS 1 W or E
W: Work done by constant force
K .E.: mv 2 P
2 t
(J) K.E: Kinetic Energy, m = mass (kg) P: Power (W)
F: Constant Force (Newton) v = velocity (m/s) W: Work done (J)
S: Displacement of force
P.E. : mgh E: Energy (J)
m = mass (kg), g = Gravity Field t: Time taken (seconds)
Strength, h = height of object (m)
Other Info. Work is done on an object only The principle of conservation of energy Efficiency
when the force applied on it states that energy cannot be created or
Useful energy output
produces motion. destroyed, but can only change from = 100%
one form to another. Total energy input
Pure Physics SA2 Overall Revision Notes
General Physics: Chapter 7
Pressure
Pressure in a solid Pressure in a liquid Pressure in a gas
Definition Pressure is the force acting normal or perpendicularly per unit area.
SI unit Pascal (Pa) or N/m2
Equation Force Pressure = h g The air surrounding us exerts a
Pressure = pressure in all directions which is
Area h: Depth of the liquid (m)
p: Density of liquid (kg/m )3 about 105 Pa.
g: Gravitational field strength
Other Info. This formula can only 1. A liquid exerts pressure because of 1. A barometer is used to measure 2009 Pure Physics SA2 Overall Revision Notes
be used for solids. its weight. pressure. It consists of an inverted
2. Liquid pressure acts equally in all tube in a dish of mercury. The
directions. This is because particles space above the mercury in the
of the water can flow and wrap tube is vacuum.
around the object. 2. Liquid mercury is used as its
Hydraulics Systems density is very high and a shorter
Purpose: Increase the output force barometer can be used to show
from an input force. However the atmospheric pressure.
height which the object can be 3. An object can be bent/sucked in
increased is reduced. due to the production of vacuum
Properties used: Liquids are and due to the difference in
incompressible and if pressure is pressure; the atmospheric
applied to trapped liquid, it is pressure will press on the object.
transmitted to all parts of the liquid.
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Pure Physics SA2 Overall Revision Notes
Thermal Physics: Chapter 8
Temperature
Temperature It is a measure of the degree of hotness of a body. Physical Properties :
1. Expansion of column of liquid
Measured using a thermometer in capillary tube
Temperature Scale 2. Voltage of thermocouple
3. Expansion of a bimetallic strip
The Celsius Scale The Kelvin Scale Desirable Features
Ice Point: Temperature of pure melting ice at Zero: Absolute Zero (where object
o 1. Easy to read scale
standard atmospheric pressure (0 C). has nothing in the body)
Steam Point: Temperature where boiling Unit: Kelvin (K). 2. Safe
3. Sensitive to temperature
water changes to steam at standard K   ( C )  273K changes
atmospheric pressure. 1oC increase = 1 K increase. 4. Wide range of temperature
General Equation Types of Thermometers
Measured Physical Property
 Clinical Thermometer, Liquid in Glass Thermometer, Thermocouple
Total Range of Physical Property
Difference between Mercury / Alcohol Thermocouple
thermometer
1. Consists of 2 wires of different materials
Mercury Alcohol joined together to form 2 junctions.
Uniform Yes No (Out of 2. A voltage is produced when the junctions are
Expansion Range) at different temperatures. It increases as the
Stick to Glass No (visible Yes temperature increases.
meniscus) (Transparent) 3. Suitable for measuring wide temperature
Reaction to Quick Slow differences, which vary rapidly due to its
temp. changes quick response and temperature at a point as
Range Measure Measure lower wire junctions are small.
Higher Temp. temp. 4. Can be connected in series to increase
Cost Expensive Cheap sensitivity.
Poisonous Yes No
2009 Pure Physics SA2 Overall Revision Notes
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Pure Physics SA2 Overall Revision Notes
Thermal Physics: Chapter 9
Kinetic Model of Matter
The kinetic theory of matter states that all matter is made up of large number of tiny atoms or molecules which are
in continuous motion.
Molecular Model of the 3 states of matter
Solid Liquid Gas
Forces between Molecules Balanced, strong As strong as solid Negligible
Distance between Small, arranged in regular Slightly further apart, no Far apart, mainly empty
molecules pattern pattern space
Motion of molecules Vibrate about fixed Vibrate to and fro Move randomly with high
positions speed, colliding with one
another and walls.
Compression No No Yes
When heated Molecules gain energy Molecules vibrate and Move at higher speed,
and vibrate more, move about more collision with one another
separation between vigorously, separation and walls increases.
molecules increase between molecules Expands the most.
slightly increase slightly
Diffusion Pressure exerted by a gas
It is the spreading of molecules on their own When a gas molecule hit the walls of the container, it
accord without any external aid. exerts a force on the container.
Occurs in liquids and gases Pressure increases when:
Occurs as particles are in random motion 1. Volume of container decreases at constant
Depends on temperature and density temperature
(concentration) of fluid. The lower the 2. Temperature of gas increases at constant volume
density, the more space for particles to 3. Number of gas molecules increase, total pressure
move into. exerted increases.
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Pure Physics SA2 Overall Revision Notes
Thermal Physics: Chapter 10
Transfer of Thermal Energy
Transfer of Thermal Energy: When 2 objects are placed in contact with one another, their
temperature eventually becomes the same, known as thermal equilibrium. Note: Heat
travels from a region of high temperature to low temperature.
Conduction Convection Radiation
Heat is transmitted layer by Process where heat is A method of heat transfer
layer through a medium from transmitted from one wher ethe source of heat
place to another by the
one particle to another. movement of heated
transmit energy through
electromagnetic waves. A
particles of a gas/liquid. medium is not required.
Collision Flow of free
between electrons Mechanism:
neighbouring (conductors Change in Factors: Temperature of object,
particles only) Density. surface of object, surface area of
object. Good emitters are also
good absorbers of radiation.
Conduction:
1. Collisions between neighbouring particles.
a. Particles nearer to heat source gain energy and vibrate faster.
b. Particles collide into less energetic neighbouring particles which gains kinetic energy.
c. The less energetic particles vibrate faster, collides into other particles.
d. Process continues layer by layer to spread the heat to cooler parts.
2. Flow of free electrons (conductors only)
a. Electrons near heat source gain energy, move faster.
b. Free electrons can move between the particles and collide with other electrons, allowing the less 2009 Pure Physics SA2 Overall Revision Notes
energetic electrons to gain energy and move faster.
c. Process continues to spread the heat to cooler parts.
Convection
3. Fluid nearer to heat source gains heat and expands.
4. Expansion causes decrease in density for the fluid nearer to heat source, causing it to rise.
5. The hotter fluid rises over the cooler fluid while the cooler fluid rushes in to take the space.
6. The process continues and a convection current is formed.
7. Convection is faster than conduction as there is bulk movement (all the molecules get hot and move up,
thus it is faster than conduction.
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Pure Physics SA2 Overall Revision Notes
Light, Waves and Sound: Chapter 12
Light
Speed: 3 x 108 Path it travels is a light ray. Can be parallel beam, converging beam or
diverging beam.
Light
Objects which give out light are luminous objects, those which doesn’t are non-luminous.
Chapter 12.1: Reflection of light
Important terms:
Incident Ray: Light ray hitting the reflecting
surface.
Reflected Ray: Light ray reflected from the
reflecting surface.
Normal: The perpendicular to the reflecting
surface at the point of incidence.
Angle of incidence (i): The angle between the
incident ray and the normal.
Angle of reflection (r): The angle between the
reflected ray and the normal.
Laws of Reflection:
The incident ray, reflected ray and the normal of the reflecting surface lie on the same plane.
Angle of incidence = Angle of Reflection
Regular Reflection Diffuse Reflection
Occurs at smooth surfaces. Occurs at rough surfaces (sandpaper, burnt
Parallel light rays incident boots). Parallel light rays incident on the
on the surface are reflected surface is reflected in all directions. The
in one direction only (all rays normals are not parallel.
have the same incident/
reflected ray). The normals of
all points of incidence are equal.
2009 Pure Physics SA2 Overall Revision Notes
Characteristics of image formed by plane mirror
Same size as object
Laterally inverted
Upright
Virtual (not real, cannot be captured on screen)
The distance of the image from the mirror = distance of
object from the mirror.
Applications of Mirrors:
Optical Testing (Mirrors can make letters appear further
away, saving space)
Blind Corners (for drivers)
Periscopes
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0

Chapter 12.2: Refraction of light
Refraction is the bending effect of light as it passes through another
medium of different density.
Refraction occurs as the speed of light varies in different media.
Conditions for refraction:
The light must pass from one optical medium to another of different
optical density
Angle of incidence more than 0°.
Laws of Reflection:
The incident ray, the normal and the refracted ray all lie on the
same plane.
For 2 particular transparent media, the ratio of the sine of the angle of incidence to the sine of the angle
sin i
of refraction is a constant.  Constant
sin r
When light travels from a less dense medium to a denser medium, the ray of light moves towards the normal.
Likewise, when light travels from a denser to a less dense medium, the ray of light moves away from the
normal.
When light enter a medium perpendicularly, regardless of its density, no deviation of the ray is observed.
When angle of When angle of incidence = Critical When angle of incidence > Critical Angle: Total
incidence < Critical Angle: Travels perpendicular to the Internal Reflection.
Angle: Normal surface (90°) Refracted ray cannot escape from the glass.
Refraction As i is made bigger, the refracted ray Refraction cannot happen and light is reflected at
gets closer and closer to the glass / air boundary.
the surface of the glass. Total Internal Reflection occurs when a ray of light
which is incident on the boundary between 2
1 1 medium is totally reflected back into the first.
Can be found by taking c  sin   Applications of Total Internal Reflection:
n Periscope and Binoculars
Optical Fibres
2009 Pure Physics SA2 Overall Revision Notes
Refractive Index Daily Phenomena of Reflection
The value of the constant ratio sin i/sin r Swimming pool appears shallower than it actually is.
for a ray passing from air/vacuum to a To find the refractive index of the medium, take
give medium is known as the refractive .
index of the medium.
The greater the value of the refractive
Bent objects in liquids. To find refractive index use same
index, the greater the bending of light,
formula as above.
the more the light is slowed down and
the denser the medium is.
Dispersion of white light. This is due to different colours
Medium Refractive Index, travelling different speeds in glass.
Diamond 2.5 Red deviates (slows down) the least.
Glass 1.4 – 1.9 Violet deviates (slows down) the most.
Water 1.33
Air 1.00
1
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Chapter 12.3: Converging Lens
Features of a converging lens
Optical Centre (C): The midway point between the lens surface on the principal axis
Principal axis: The line passing symmetrically through the optical centre of the lens
Principal focus (F): Point on the principal axis where rays of light converge after passing through the lens
Focal length (f): Distance between the optical centre, C and the principal focus F.
Focal plane: Plane which passes through F and P. It is perpendicular to principal axis.
As light rays can pass through the lens from both sides, each lens has 2 principal foci and 1 focal length on
each side of the lens.
A thicker lens has a shorter focal length and bends light rays to a greater extent whereas a thinner lens has a
longer focal length and bends light rays to a shorter extent.
Height of Image Image Distance
Linear magnification, m, is defined as or .
Height of Object Object Distance
Action of a thin converging lens on a
parallel beam of light parallel to the
principal axis.
Object Properties of Image Uses
distance Image Distance
Object
Focal length
distance is Object lens of a
opposite of Action of a thin converging lens on a
infinity telescope
Inverted, real, lens parallel beam of light NOT parallel to
(parallel rays)
2009 Pure Physics SA2 Overall Revision Notes
diminished
Object Between 1 the principal axis.
(smaller)
distance is and 2 focal
Camera, eyes
more than 2 length
focal lengths opposite lens
Object Photocopier
Inverted, real, 2 focal length
distance is 2 (equal sized
same size opposite lens
focal length copy)
Object
More than 2 Projector,
distance Inverted, real,
focal length photograph
between 1 and magnified
opposite lens enlarger
2 focal length
Object
Infinity, same
distance is 1 Spotlight
side of lens
focal length Upright,
Object magnified,
Image behind
distance is less virtual
object, same
Magnifying 1
than 1 focal glass
side of lens
length 2

Pure Physics SA2 Overall Revision Notes
Light, Waves and Sound: Chapter 13
Waves
A wave is a phenomenon in which energy is transferred through vibrations.
Waves
Properties of waves:
1. The source of any wave is a vibration or oscillation.
2. Waves transfer energy from 1 point to another.
3. In waves, energy is transferred without the medium being transferred.
1. Transverse waves are waves that travel
perpendicular to the direction of motion.
2. Examples of such waves include rope waves and
water waves.
3. The crest is the highest points of the wave
whereas the trough is the lowest points of the
wave.
1. Longitudinal Waves are waves that travel parallel
to the direction of motion.
2. Examples are sound wave and pressure waves.
3. They form compressions and rarefactions.
4. Compressions are region where the air particles
are close together, creating high pressure.
5. Rarefactions are areas where the air particles are
far apart, creating low pressure.
Wave Terms
2009 Pure Physics SA2 Overall Revision Notes
1. A wavelength is the shortest distance between any 2 1. Wavefront: This is an imaginary line on a live
corresponding points in a wave. SI unit: metre. that joints all points that are in the same phase.
2. Symbol:  2. It is usually drawn by joining the wave crests.
3. Amplitude is the maximum displacement from the rest
or centre position (high of a crest or depth of a trough).
SI unit: metre.
1. Frequency (f):It is the
number of complete
waves per second. In
other words, the
number of occurrences
within a given time
period.
2. When there is a higher 4. Period (T): This is the time taken for 1 point on
frequency, more waves the wave to complete 1 oscillation. In order
are produced in 1 words, it is the time taken to produce 1 wave.
second, thus the period 5. The SI Unit is seconds (s). 1
will be shorter.
3. SI unit: Hertz (Hz). 3

1. Wavespeed: It is the distance of the
wave moved in 1 second in the medium.
It is dependent of the medium itself. For
example, for sound, the wavespeed is
always the same unless the medium is
changed from solid to liquid.
2. Real life example: If the crest of an ocean
wave moves a distance of 20 meters in 10
seconds, then the speed of the ocean wave is 2
m/s. On the other hand, if the crest of an ocean
wave moves a distance of 25 meters in 10
seconds (the same amount of time), then the
speed of this ocean wave is 2.5 m/s. The faster
wave travels a greater distance in the same
amount of time.
3. It is measured in metre per second.
Chapter 13.6: Graphical Representation of Waves
A displacement-position graph shows how high or low a A displacement-time graph shows the displacement
wave is at a particular position. of a single particle at a particular position o the
particle as time changes
Both graphs can be used to represent a longitudinal or transverse wave.
Chapter 13.7: Refraction and Reflection of Waves
1.) When water waves get reflected, the only thing
that changes is the direction. The wavelength,
frequency and speed remains the same
throughout. Sponges are used to absorb the
2009 Pure Physics SA2 Overall Revision Notes
reflections of the water waves.
2.) When water waves get refracted (move from
deep to shallow water), the speed and the
wavelength changes. The frequency of the wave
does not change1.
Shallow
Deep water
water
Faster
Slower speed
speed2
Longer Shorter
wavelength wavelength
Similar Frequency
1
It only changes if the source of the waves is changed (e.g. vibrating faster)
1
2
This is due to the wave having more energy in deep water (more space)
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Pure Physics SA2 Overall Revision Notes
Light, Waves and Sound: Chapter 14
Electromagnetic Spectrum
1.) Electromagnetic waves are transverse
waves. They are electric and magnetic fields
that oscillate at 90° to each other.
2.) They transfer energy from one place to
another.
3.) They can travel through vacuum (do not
require any medium to travel)
4.) They travel at 3.0 x 108 per second in
vacuum. They will slow down when
travelling through water or glass.
5.) The wave equation is applicable here too.
6.) They obey the laws of reflection and
refraction.
7.) They carry no electric charge (they are
neither positively or negatively charged)
8.) Their frequencies do not change when
travelling from one medium to another. Only
their speeds and wavelength will change.
Uses of Electromagnetic Waves
Wave Uses Dangers
Radio transmitters
Radio Waves Radar None
Television
Microwave ovens
Microwaves Internal heating of body tissue
2009 Pure Physics SA2 Overall Revision Notes
Communication system
Thermal imaging
Infra-red Burns skin
Remote controls
Optic fibres
Light Strong light causes damage to vision.
Seeing!
Washing powder (whiter than
Ultra-violet white) Skin cancer and blindness
Security marking
X rays Taking images of the skeleton Mutations in cells and severe burns to the skin.
Cancer treatment
Gamma Rays Cancers and cell mutation
Sterilisation of equipment
1
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Pure Physics SA2 Overall Revision Notes
Light, Waves and Sound: Chapter 15
Sound
Sound is a form of energy. The energy is passed from 1 point to another as a wave.
Sound
Sound is an example of longitudinal wave.
Sound is produced by vibrating sources placed in a medium (air).
It travels in air through a series of compressions or rarefactions.
Compressions: Air molecules are close together, forms high pressure.
Rarefactions: Air molecules are far apart, forms low pressure.
2.) Speed of sound differs in different medium.
Air: 330 - 340m/s
Water: 1500m/s
Glass:5000m/s
3.) Speed of sound differs because:
Differences in strength of interatomic forces Echoes
Closeness of atoms in the 3 states 6.) Echoes refer to the repetition of a sound
Temperature resulting from reflection of the sound
waves.
4.) The Wave Equation can also be used to find the speed of 7.) Echoes are formed when a sound is
sound (refer to page 11) reflected off a hard and flat surface.
8.) Reverberation occurs when the surface is
5.) The speed of sound is solids like metals are so fast that too close, causing any reflected sound to
we can assume/ignore the time it takes to travel a follow closely behind the direct sound and
distance. prolonging the original sound.
Ultrasound Loudness and Pitch
9.) The range of frequencies which a person can hear is
known as the range of audibility.
Human: Between 20 Hz and 20 kHz1
Dog: <20 kHz
Bats: Between 10 kHz and 120 kHz.
2009 Pure Physics SA2 Overall Revision Notes
10.) Ultrasound is the sounds with frequencies above
the upper limit of the human range of audibility. Its
small wavelength means less diffraction and the
echo formed is more precise in direction.
11.) Applications for ultrasound include: 12.) Loudness is a factor distinguishing between
Determining depth of seabed various sounds.
Locating sunken ships / shoals of fish The larger the amplitude of vibration, the louder
Cleaning small dirt from jewellery. the sound
Quality control (checking for cracks) in concrete Sound is measured by decibels (dB).
Medical applications (development of foetus)
13.) Pitch is a factor distinguishing various sounds
The higher the frequency of a note, the higher
the pitch
Pitch is measured in hertz (Hz).
1
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