AS-LEVEL
PHYSICS
Revision Notes
CONTENTS
UNITS, SYMBOLS AND NUMBERS
MOTION
DYNAMICS
WORK AND ENERGY
VECTORS, MOMENTS AND PROJECTILES
WAVES
OPTICS
MATERIALS
2
3
4
5
6
7-9
10
11
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UNITS, SYMBOLS AND NUMBERS
5 BASE UNITS:
Base Quantity
Length
Mass
Time
Current
Temperature
Base Unit
Metre
Kilogram
Seconds
Ampere
Kelvin
Base Symbol
m
kg
s
A
K (100°C + 273 = K)
Area = length x width  m2
Volume = length x width x height  m3
Average speed = distance/time  m s-1
Density = mass/volume  MV-1 = kgm-3
DERIVED UNITS:
Unit Quantity
Force
Power
Energy
Base Unit
kg m s-2
kg m2 s-3
kg m2 s-2
Unit Name
Newton
Watt
joule
Unit Symbol
N
W
J
POWERS OF 10:
Power of 10
102
103
106
1026
10-3
10-6
10-18
Value
100
1000
1000000
100000000000000000000000000
0.001
0.000001
0.000000000000000001
MULTIPLES AND SUBMULTIPLES:
Power of 10
1012
109
106
103
10-2
10-3
10-6
10-9
10-12
10-13
Prefix
Tera
Giga
Mega
Kilo
Centi*
Milli
Micro
Nano
Pico
Femto
Symbol
T
G
M
k
c
m
μ
n
p
f
EQUATIONS OF MOTION:
v = u + at
s = ut+ ½ at2
s = (u+v) t
2
2
2
v = u +2as
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MOTION
SPEED:
Definition: CHANGE IN DISTANCE PER UNIT TIME
Average speed = distance/time
Measured in: m s-1
SCALAR QUANTITY – has size but not direction
DISPLACEMENT:
Definition: DISTANCE MEASURED IN A STRAIGHT LINE FROM A SPECIFIC POINT
Symbol: ‘s’
VECTOR QUANTITY – has both size and direction
VELOCITY:
Definition: CHANGE IN DISPLACEMENT PER UNIT TIME
Velocity = change in displacement/ change in time  s/t
Measured in: m s-1
VECTOR QUANTITY – has both size and direction
GRADIENT:
Change in Y/ change in X
Of a displacement vs. Time graph
Of a velocity vs. Time graph
Y = MX + C
Equal to velocity
Equal to acceleration
ACCELERATION:
Definition: VELOCITY CHANGE PER UNIT TIME
Acceleration = v/ t
Measured in: m s-2
VECTOR QUANTITY – has both size and direction
Uniform acceleration: DESCRIBES AN ACCELERATION IN WHICH THE VELOCITY CHANGES BY
THE SAME AMOUNT EACH SECOND
Non-uniform acceleration: DECRIBES AN ACCELERATION IN WHICH THE VELOCITY CHANGE
EACH SECOND VARIES
DEFINTIONS:
Precision of an instrument: SMALLEST NON-ZERO READING AN INSTRUMENT CAN MEASURE
Random error: AN UNPREDICTABLE SOURCE OF UNCERTAINTY IN A MEASUREMENT WHICH
LEADS TO AN INCONSISTENCY IN REPEATS OF THAT MEASUREMENT
Range: LARGEST REPEAT MEASUREMENT – SMALLEST REPEAT MEASURE OF ONE DATA SET
Uncertainty: ½ x RANGE
Percentage uncertainty: UNCERTAINTY/ AVERAGE VALUE x 100
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DYNAMICS
FOUR FORCES IN NATURE:
Forces
STRONG NUCLEAR FORCE
WEAK NUCLEAR FORCE
ELECTROMAGNETIC FORCE
GRAVITATIONAL FORCE
Detail
Hold Protons and Neutrons together in the nucleus
Involved in radioactive decay  C-14
Responsible for attractive and repulsive forces between
atoms e.g. air resistance, friction
Gravity is the dominant force in the universe for shaping
the large scale structure of galaxies and stars
GRAVITY:
Definition: GRAVITATIONAL FIELD STRENGTH IS THE FORCE OF GRAVITY ON A MASS OF 1
KILOGRAM
Force of gravity on an object  object’s weight
Measured in: N kg-1
Symbol for gravitational field strength: ‘g’
Acceleration due to gravity = gravitational field strength
Force of gravity = weight = mg
FRICTION:
Definition: FRICTION FORCE  FORCE EXERTED BY A SURFACE AS AN OBJECT MOVES ACROSS
OR MAKES AN EFFORT TO MOVE ACROSS THAT SURFACE. FRICTION OPPOSES THE
MOTION OF AN OBJECT
Depends upon NATURE of the two surfaces and upon the DEGREE to which they are pressed together
Frictional forces acting on an object moving through a gas or liquid are also known as ‘fluid friction’,
‘drag’ and ‘air resistance’
NORMAL CONTACT FORCE  acts at 90° to the surface in contact
RESULTANT FORCE: overall/net effect of all the forces on an object (A.K.A unbalanced force)
ISSAC NEWTON’S LAWS:
1st Law:
EVERY OBJECT REMAINS AT REST OR CONTINUES IN A STRAIGHT LINE WITH CONSTANT
VELOCITY UNLESS ACTED UPON BY A RESULTANT FORCE
2nd Law:
THE ACCELERATION OF AN OBJECT IS DIRECTLY PROPORTIONAL TO RESULTANT FORCE
ACTING ON THAT OBJECT. This law is summarised by the formula; F=ma
3rd Law:
EVERY ACTION HAS AN EQUAL AND OPPOSITE REACTION
Or
IF BODY A EXERTS A FORCE ON BODY B THEN BODY B WILL EXERT AN EQUAL BUT OPPOSITE
FORCE ON BODY A
DEFINITIONS:
Newton: A FORCE OF ONE NEWTON GIVES A MASS OF 1 kg AN ACCELERATION OF 1 m s-2
Terminal Velocity: ACHIEVED WHEN THERE IS NO RESULTANT FOCE ACTING ON A FALLING
BODY
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WORK AND ENERGY
WORK:
Definition: WORK = FORCE APPLIED x DISPLACEMENT IN THE DIRECTION OF THE FORCE
Measured in: N m (Newton Metre) or J (Joule)
In physics, mechanical work is done when a force moves
Work equation: W = Fs
Effect a force has in a particular direction is called a COMPONENT
Require a COMPONENT TRIANGLE to calculate a component
COMPONENT TRIANGLE: a right-angled triangle in which the force (F) forms the hypotenuse
W = FsCOSθ
or W = FsSINθ
ENERGY:
POTENTIAL ENERGY: energy stored within a system as a result of position or condition
KINETIC ENERGY: energy of motion
Any system or object that has energy has the ability to DO WORK
Principle of Conservation of Energy: ENERGY CANNOT BE CREATED OR DESTROYED. IT CAN
ONLY BE CHANGED FROM ONE FORM TO ANOTHER
Work-Energy Principle: THE CHANGE OF ENERGY OF AN OBJECT IS EQUAL TO THE NET WORK
DONE ON THE OBJECT
Translational Kinetic Energy Equation: Ek
= ½ mv2
Gravitational Potential Energy Equation: Ep = mgh
POWER:
Definition: POWER IS THE WORK DONE PER UNIT TIME (A.K.A) RATE OF DOING WORK
Measured in: J
s-1 (A.K.A 1 W)
Power = work done/ time interval  W/t
Useful Engine Output Equation: P = W/t  P = Fs/t  P = Fv  (v = s/t)  P=
Fv
EFFICENCY:
Efficiency: useful output power/ input power
FORCE vs. DISTANCE GRAPHS:
Area of a graph = WORK DONE
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VECTORS, MOMENTS AND PROJECTILES
VECTORS:
Definition: A QUANTITY WHICH HAS DIRECTION AS WELL AS SIZE
Components of a Vector Calculation: Fx = Fcos°  horizontal component
Fy = Fsin°  vertical component
Vector Diagram: tail of one arrow starts at the head of the previous arrow
CENTRE OF MASS OF A BODY:
Definition: THE POINT THROUGH WHICH A SINGLE FORCE ON THE BODY DOES NOT CAUSE THE
BODY TO TURN
MOMENTS:
Definition: MOMENT = FORCE x PERPENDICULAR DISTANCE FROM THE PIVOT TO THE LINE OF
ACTION OF THE FORCE
Moment = Fd
Principle of Moments: FOR AN OBJECT THAT IS IN EQUILIBRIUM THE TOTAL CLOCKWISE
MOMENT ABOUT A POINT IS EQUAL TO THE TOTAL CLOCKWISE
MOMENT ABOUT THE SAME POINT
Equilibrium: A SYSTEM IS IN EQUILIBRIUM IF THERE IS NO RESULTANT FORCE AND NO
RESULTANT MOMENT
Moment Of A Couple: ONE FORCE x PERPENDICULAR DISTANCE BETWEEN THE LINES OF
ACTION OF THE TWO FORCES (A.K.A: Torque)
Moment Of A Couple = (½F)d
PROJECTILES:
Definition: A PROJECTILE IS A MOVING OBJECT ON WHICH THE ONLY FORCE ACTING IS
GRAVITY
Vertical component of velocity is INDEPENDENT of the horizontal component of velocity
A bullet shot from a gun follows a PARABOLIC path; slight arc (rainbow shaped)
Acceleration is ±9.81 (due to gravity)
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WAVES
WAVES:
Definition: A WAVE IS A DISTURBANCE WHICH CAN TRAVEL, USUSALLY TRANSFERRING
ENERGY
Wave Speed: DISTANCE TRAVELLED BY A WAVE FRONT PER UNIT TIME
Continuous wave: IN A FULL CYCLE OF VIBRATION, ONE POINT IN THE MEDIUM MOVES FROM
ITS EQUILIBRIUM POSITION TO ONE EXTREME TO THE OTHER EXTREME
AND BACK TO THE EQUILIBRIUM POSITION
Transverse Waves: DIRECTION OF VIBRATION IS AT 90 TO THE DIRECTION THE WAVE IS
TRAVELLING
Longitudinal Waves: MEDIUM OSCILLATES PARALLEL IN THE SAME DIRECTION THE WAVE IS
TRAVELLING
Mechanical Waves: REQUIRE A SUBSTANCE TO TRAVEL THROUGH  MATERIAL THAT CARRIES
A MECHANICAL WAVE IS CALLED A MEDIUM
Displacement Of A Point In The Medium: IS ITS DISTANCE AND DIRECTION FROM ITS
EQUILIBRIUM POINT
Frequency Of Vibration: NUMBER OF CYCLES OF VIBRATION IN ONE SECOND (measured in Hz)
Time Period: TIME TAKEN FOR ONE CYCLE OF VIBRATION
In Phase: DESCRIBES TWO POINTS IN THE MEDIUM THAT ARE MOVING IN THE SAME
DIRECTION AND CHANGE DIRECTIONAT THE SAME INSTANT
Wavelength: THE DISTANCE BETWEEN TWO CONSECUTIVE POINTS THAT ARE IN PHASE (λ)
Amplitude: THE MAXIMUM DISPLACEMENT OF A VIBRATING POINT IN THE MEDIUM
Phase Difference: THE AMOUNT BY WHICH ONE VIBRATION LAGS BEHIND ANOTHER. Measured in
degrees
½ cycle of vibration lag = phase difference of 180°
¼ cycle of vibration lag = phase difference of 90°
1/8 cycle of vibration lag = phase difference of 45°
WAVE SPEED: c
= fλ
REFLECTION OF WAVES:
Definition: ALL POINTS IN THE MEDIUM ALO A PARTICULAR WAVEFRONT ARE VIBRATING IN
PHASE
REFRACTION: the bending of a wave due to a change of speed
DIFFRACTION OF WAVES:
Definition: THE BENDING OF WAVES AS THEY PASS THROUGH A GAP OR PASS BY AN OBSTACLE
Maximum diffraction occurs when the gap is similar in size to the wavelength
SUPERPOSITION:
Principle of Superposition: AT A POINT WHERE TWO WAVES MEET, THE TOTAL DISPLACEMENT IS
THE SUM OF THE DISPLACEMENTS DUE TO THE INDIVIDUAL WAVES
What happens when the waves from two machines meet?
They pass through each other, but, when they overlap they combine; when a crest meets a
crest a double sized crest is produced, when a trough meets a trough a double sized trough
is produced. But when a crest meets a trough they cancel each other out.
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Pattern produced by two wave sources that are side-by-side is called INTERFERENCE FRINGES
Crest + Crest = Super-crest (superposition)  constructive interference
Trough + Trough = Super-trough (superposition)  constructive interference
Trough + Crest = cancelled (straight line)  destructive interference
COHERENT SOURCES:
Definition: COHERENT SOURCES OF WAVES ARE SOURCES WHICH ARE POSITIONED SIDE BY
SIDE, HAVE THE SAME FREQUENCY AND ARE VIBRATING IN PHASE
Need to determine the number of wavelengths from one wave source to a particular point
Determine the number of wavelengths from other wave source to same particular point
PATH DIFFERENCE: extra distance travelled by the wave from one source compared with the wave
from the other source.
Integer means it’s constructive, decimals means it’s destructive interference
INTERFERENCE FRINGES:
Distance from centre of one bright fringe to centre of next is called the FRINGE SPACING  symbol
‘w’, ‘D’ is distance from slits to screen, ‘s’ is slit separation
W = λD
S
GRATING:
Equation: nλ = d sin θ
WHAT DO DIFFRACTION AND INTERFERENCE EXPERIMENTS TELL US
ABOUT THE NATURE OF LIGHT?
The observation that light can undergo double slit interference and diffraction with a grating shows that
light also has wavelike properties
HOW DO WE KNOW THAT LIGHT BEHAVES AS A TRANSVERSE WAVE?
The fact that we can POLARISE light tells us that light behaves as a transverse wave
Definition: the transmission axis of a Polaroid (polarising filter) is the direction of the vibrations that it
will transmit
Definition: unpolarised light has vibrations in many directions (but all still at 90° to the direction of
travel)
Definition: plane polarised light has vibrations is only one direction
A longitudinal wave cannot be polarised  light must have transverse vibrations because it can be
polarised
STATIONARY WAVES:
Points on a medium (e.g. string) don’t move  the nodes
How ware stationary wave patterns formed?
To get a stationary wave pattern we need two waves that have the same speed, wavelength and
frequency, and approximately the same amplitude. The incident wave travels along the string to the
opposite end where it is reflected. The superposition of the incident and reflected wave creates a
stationary wave pattern.
Fundamental vibration  1st overtone (double the fundamental)  2nd overtone (triple the
fundamental)  3rd overtone (quadruple the fundamental)
At nodes the incident and reflected waves interfere destructively
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At antinodes the incident and reflected waves interfere constructively
NODE TO NODE separation = ½ λ
The vibration of strings gives the appearance of ‘loops’. Due to the ‘persistence of vision’.
Within one node-to-node loop all the ‘bits’ on the string vibrate in phase
Adjacent node-to-node loops vibrate 180° out of phase (A.K.A anti-phase)
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OPTICS
LAW OF REFLECTION:
Angle of incidence = angle of reflection
Angles of incidence and reflection are measured between the ray and the normal
REFRACTION:
Definition: THE BENDING OF WAVES DUE TO A CHANGE IN SPEED
When a beam of light travels from a less dense to a denser material, the beam is bent towards the normal.
REFRACTIVE INDEX OF A SUBSTANCE: n = speed of light in a vacuum
speed of light in the substance
 c/
cs (no units)
SNELL’S LAW OF REFRACTION:
Law of refraction: n1 sin θ1 = n2 sin θ2
Angle of incidence 1 = θ1
Angle of incidence 2 = θ2
Refractive index of medium 1 = n1
Refractive index of medium 2 = n2
Refractive index of air to 4 s.f.  1.000
CRITICAL ANGLE: θc is equal to the incident angle within a substance which results in a refracted ay
having an angle of refraction of 90°
TOTAL INTERNAL REFLECTION:
OCCURS WHEN: the substance containing the incident angle has the larger refractive index, AND the
incident angle is greater than the critical angle for the interface.
CRITICAL ANGLE FORMULA:
Sin θc = n2
n1
OPTICAL FIBRE:
CONSISTS OF: a core of glass surrounded by cladding made of glass of a different refractive index. Light
from a laser travels along the optical fibre.
PURPOSE OF CORE: light travels along the core undergoing TOTAL INTERNAL REFLECTION at the
boundary between the core and the cladding.
PURPOSE OF CLADDING: prevents light from escaping from the optical fibre. Ensures that the light can
travel significant distances via an optical fibre. Also – if fibre is used for
communications – it keeps the information being sent as a series of light
pulses secure (prevents fraud).
MULTIPATH DISPERSION: can be reduced by making core of optical fibres very thin – shortens journey
of light pulses.
USES OF OPTICAL FIBRES:
COMMUNICATIONS: advantage  information can be transmitted at high speed
MEDICINE: endoscopes  advantage of producing more accurate medical diagnoses; produce images of
inside of body.
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MATERIALS
DENSITY:
Definition: DENSITY IS MASS PER UNIT VOLUME
Most commonly used units for density are g
cm-3 and kg m-3
HOOKE’S LAW:
For a material which obeys Hooke’s law the extension is DIRECTLY PROPORTIONAL to the stretching
force PROVIDED the limit of the proportionality has not been exceeded.
A material which obeys Hooke’s law would therefore have a force vs. extension graph which is a straight
line through the origin
A material which has a permanent stretch once the load has been removed is said to have been stretched
beyond its elastic limit
The area between the loading curve and the extension axis is equal to the work done in stretching the
rubber band. This is equal to the energy stored in the stretched rubber band
The area between the unloading curve and the extension axis is equal to the work done by the rubber band
as it raises the load whilst the load is being reduced
The difference between the areas values calculated for loading and unloading is equal to the energy
converted to internal energy (heat) of the rubber band during the experiment. Hence repeatedly stretching
and unstretching a rubber band warm the rubber band
Enclosed area = area loading – area unloading  energy converted to internal energy
F x e = (force x extension)  FL
GRADIENT OF A GRAPH: F
L
The point on the force vs. Extension graph just before the initial straight line starts to bend is called the
LIMIT OF PROPORTIONALITY
Definition: the ELASTIC LIMIT is the amount that a material can be stretched and still return to its
original length
A material which stretches a lot after its elastic limit has been exceeded is described as a DUCTILE
material
A material which breaks soon after its elastic limit is described as a BRITTLE material
If a material has been stretched beyond its elastic limit it has undergone PLASTIC DEFORMATION. This
means that the atoms in the material have permanently changed their position relative to each other
WHAT HAPPENS TO THE MOLECULES OF A RUBBER BAND DURING
STRETCHING?
BEFORE STRETCHING: rubber is made up of long chain molecules which are very tangled up
DURING STRETCHING: the rubber band is quite stiff to start with because the molecules are so tangled
AS STRETCHING CONTINUES: the molecules untangle more easily. The rubber band stretches more
readily
MORE STRETCHING FORCE APPLIED: once the molecules are untangled, any more stretching has to
try to overcome the forces between atoms in the chain. This
is difficult because there are strong forces between atoms,
hence the rubber band is now very stiff
TENSILE STRESS, STRAIN AND YOUNG’S MODULUS:
Definition: TENSILE STRESS  THE STRETCHING FORCE PER UNIT CROSS-SECTIONAL AREA
Measured in: 1 N m-2  1 pascal (1 Pa)
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Formula:
TS = F/A
Definition: TENSILE STRAIN  EXTENSION PER UNIT LENGTH
NO UNITS
Formula: L/L (L = original length)
Definition: YOUNG’S MODULUS  TENSILE STRESS/ TENSIL STRAIN ( before limit of
proportionality)
Measured in: N m-2
A Stiffer material has a bigger Young’s modulus value
SPRINGS:
HOOKE’S LAW: the force needed to stretch a spring is directly proportional to the extension of the spring
from its natural length provided the spring’s proportional limit is not exceeded
Definition: IF A SPRING IS STRETCHED BEYOND ITS ELASTIC LIMIT, IT WILL NOT RETURN TO ITS
INITIAL LENGTH WHEN THE STRETCHING FORCE IS REMOVED
Force = constant x extension
F = k L
Definition of a spring constant: STRETCHING FORCE PER UNIT EXTENSION  measured in N
Elastic strain energy stored in a stretched spring = ½
m-1
FL
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