# Physics Notesx - onetrillionatar

Urban and Civil

Nov 16, 2013 (3 years and 1 month ago)

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Physics Revision
Notes

Physics Notes

1.1 Identify that a typical journey involves speed changes

A typical journey is not conducted with a constant velocity, but in fact the speed changes all the
time, hence there is an average speed for the journey.

1.2 Distinguish

between the instantaneous and average speed of vehicles and other bodies

Instantaneous speed is the speed the vehicle is travelling at that precise moment, while average
speed is the speed it is travelling over a period of time.

1.3 Distinguish between sc
alar and vector quantities in equations

Scalar quantities have no direction e.g. mass while vector quantities do have a direction e.g.
velocity in direction of motion

1.4 Compare instantaneous and average speed with instantaneous and average velocity

Speed

is a scalar and has no direction, while velocity has a direction and relates to displacement

1.5 Define average velocity as change in displacement over change in time

Average velocity is the displacement over time

2.1 Describe the motion of one body re
lative to another

Relative velocity of A to B= relative velocity of A to C
-

relative velocity of B to C

2.2 Identify the usefulness of using vector diagrams to assist solving problems

Vector diagrams need to be used to calculate displacement and the direc
tion in motion
problems

2.3 Explain the need for a net external force to act in order to change the velocity of an object

An object is not moving as it has a balanced force acting upon it, all forces cancel and hence it
does not move or change velocity.
An external force creates a net unbalanced force, changing
its velocity.

2.4 Describe the actions that must be taken for a vehicle to change direction, speed up and
slow down

A net unbalanced force is needed to change a vehicle's direction or speed

2.5
Describe the typical effects of external forces on bodies including: friction between
surfaces, air resistance

Friction between surfaces create drag and an external force that pulls the vehicle back as does
air resistance. In most cases these are negligib
le.

2.6 Define average acceleration as change in velocity over change in time and hence final
velocity
-

initial velocity over time

Average acceleration = change in velocity/ time = final velocity
-

initial velocity/ time

2.7 Define the terms mass and wei
ght with reference to the effects of gravity

Mass is the amount of matter an object has, measured in kg. Weight is the acceleration of mass
due to gravity (9.8m/s2) and is measured in newtons.

2.8 Outline the forces involved in causing a change in the
velocity of a vehicle when: coasting
with no pressure on the accelerator, pressing on the accelerator, pressing on the brakes,
passing over an icy patch on the road, climbing and descending hills, following a curve in the

Momentum, force of gravity, f
orce pushed up by the road, drag etc.

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2.8 Interpret Newton's Second Law of Motion and relate it to the equation Net force = mass x
acceleration

A force is applied to a mass when there is acceleration

2.9 Identify the net force in a wide variety of situatio
ns involving modes of transport and
explain the consequences of the application of the net force in terms of Newton's Second Law
of Motion

As long as a vehicle (with mass) has an acceleration it has a net force acting upon it, hence it
will be changing vel
ocity etc. If there is no acceleration, either in constant velocity or
stationary, then it has no force.

3.1 Identify that a moving object possesses kinetic energy and that work done on that object
can increase that energy

An object gains potential ener
gy when work is done, e.g. lifted an object, that object has energy
in it, as soon as it is moving it has kinetic energy.

3.2 Describe the energy transformations that occur in collisions

Because the vehicle has kinetic energy, it is transferred to the grou
nd or object it collided to.

3.3 Define the law of conservation of energy

Energy cannot be lost or created, it can only be transformed

4.1 Define momentum as p= mass x velocity

Momentum= mass x velocity

4.2 Define impulse as the product of force and tim
e

Impulse is the change in momentum, which is equal to force x change in time

4.3 Explain why momentum is conserved in collisions in terms of Newton's Third Law of
Motion

For every reaction, there is an equal but opposite reaction, momentum is conserved w
ith the
other equal reaction

5.1 Define the inertia of a vehicle as its tendency to remain in uniform motion or at rest

Inertia is the tendency to remain at uniform motion or at rest.

5.2 Discuss reasons why Newton's First Law of Motion is not apparent i
n many real world
situations

The law assumes there is no apparent loss in speed of the object having inertia, however there
is friction so it does not seem apparent.

5.3 Assess the reasons for the introduction of low speed zones in build up areas and the
addition of air bags and crumple zones to vehicles with respect to the concept of impulse and
momentum

Low speed zones require less time to reduce the car's speed, while air bags decrease force
while increasing time, and crumple zones reduce force on the o
ccupants.

5.4 Evaluate the effectiveness of some safety features of motor vehicles

Seatbelt increases the surface area so the force is more evenly distributed over the body while
it increases the time taken for the occupant to slow down, decreasing force.

It also avoids the
occupant colliding with interior objects.

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Physics Revision
Notes

Electrical Energy in the Home

1.1 Discuss how the main sources of domestic energy have changed over time

Wood
-

could be used as fuel source for heat and fire

Domesticated animals
-

source of
mechanical energy, heavy burdens machines e.g. ploughs or
grindstones

Wind/ water
-

Windmills

Coal
-

Superior energy coal, steam engine, production of steel and industry

Coal/ Gas
-

electrical production

Nuclear Power
-

electrical production

Hydro
-
electric
-

el
ectrical production

1.2 Assess some of the impacts of changes in and increased access to, sources of energy for a
community

A community could now continue activities after dark, or increase industry and economic
workings with sources of energy. Communicat
ion, electrical devices could be used. However
introduction of coal introduced pollution and smog.

1.3 Discuss some of the ways in which electricity can be provided in remote locations

Solar panels, portable generators

2.1 Describe the behaviour of elec
trostatic charges and the properties of the fields associated
with them

Electrostatic charges such as protons and electrons carry an electric charge (+ and
-

respectively). Magnitudes are the same. Positives repel, negatives repel, both attract each
othe
r. Neutrons have no charge and do not experience electric forces.

2.2 Define the unit of electric charge as the coulomb

The SI unit for electric charge is a coulomb. The charge on an electron is approximately
1.6x10^
-
19. Hence one coulomb is equal to th
e total charge of 6.25 x 10^18 electrons/protons.

2.3 Define the electric field as a field of force with a filed strength equal to the force per unit
charge at that point, E= F/q

Electric field strength= Force/ charge (Newtons/ coulomb). Electric field st
rength has a
direction!

2.4 Define electric current as the rate at which charge flows (coulombs/ second or amperes)
under the influence of an electric field

Current is the rate at which charge flows (moving charges are charge carriers). This is measured
i
n amps (or amperes) It is the amount of current flowing when one coulomb flows through a
second (coulomb per second) which is 6.25x10^18 electrons.

2.5 Identify that current can be either direct with the new flow of charge carriers moving in
one directi
on or alternating with the charge carriers moving backwards and forwards
periodically

DC (direct current) means that the charge carriers move in one direction

AC (alternating current) means that the charge carriers move back and forth periodically

2.6
Describe electric potential difference (voltage) between two points as the change in
potential energy per unit charge moving from one point to the other (joules/ coulomb or
volts)

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The voltage or electrical potential is the different in potential energy be
tween two points,
hence joules/ coulomb (V = W/q) or force/ distance

2.7 Discuss how potential difference changes at different points around a DC circuit

Potential difference changes before and after a resistor and before and after a power supply.

2.8 Iden
tify the difference between conductors and insulators

Conductors conduct electricity while insulators do not otherwise known as resistors.

2.9 Define resistance as the ratio of voltage to current for a particular conductor R= V/I

Ohms Law states there is a

relationship between voltage current and resistance V= IR, or R= V/I

2.10 Describe qualitatively how each of the following affects the movement of electricity
through a conductor, length, cross sectional area, temperature, material

Longer the length of th
e conductor, more resistance, larger cross sectional area, more area to
pass through
-

less resistance, higher temperature, more resistance and the different materials
affect resistance.

3.1 Identify the difference between series and parallel circuits

Ser
ies circuits have all resistors on one branch, while parallel circuits have more than two
branches.

3.2 Compare parallel and series circuits in terms of voltage across components and current
through them

Series
-

Voltage is shared, while current is the same

Parallel
-

Voltage is same, current is shared.

3.3 Identify uses of ammeters and voltmeters

Ammeters measure current, while voltmeters measure voltage

3.4 Explain why ammeters and voltmeters are connected differently in a circuit

Ammeters need to be in ser
ies to read the current while voltmeters are connected in series,
since they need to measure the potential difference, over a section of the circuit.

3.5 Explain why there are different circuits for lighting, heating and other appliances in a
house

Paralle
l circuits are used around the house, each with a fuse and separate circuits so that if one
branch downs the others don't. Each have a maximum current for safety, no point having one
circuit around the house too much current.

4.1 Explain that power is t
he rate at which energy is transformed from one from to another

Power= voltage x current. Hence the rate at which energy is transformed from one to another

4.2 Identify the relationship between power, potential difference and current

P= voltage x current
(watts)

4.3 Identify that the total amount of energy used depends on the length of time the current is
flowing and can be calculated using Energy = V x I x t

Energy = power x time, or v x I x t. It is how much power over time used. Measured in kilowatt
hours.

4.4 Explain why the kilowatt
-
hour is used to measure electrical energy consumption rather
than the joule

The joule is too small and kilowatt hour is used because it takes into account time and is much
larger.

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Physics Revision
Notes

5.1 Describe the behaviour of the
magnetic poles of bar magnets when they are brought close
together

Like poles repel, unlike poles attract. Lines flow from North to South

5.2 Define the direction of the magnetic field at a point as the direction of force on a very
small north magnetic p
ole when placed at that point

If like poles, repel, if unlike poles they attract

5.3 Describe the magnetic field around pairs of magnetic poles

Lines flow from north to south, in equal spacing. Pole rule applies.

5.4 Describe the production of a magnetic
field by an electric current in a straight current
-

carrying conductor and describe how the right hand grip rule can determine the direction of
current and field lines.

Using your right hand, do a thumbs up and align with diagram. Fingers curling around
d
emonstrate the direction of current while thumb points to the magnetic field, which points to
north.

5.5 Compare the nature and generation of magnetic fields by solenoids and a bar magnet

A solenoid uses an electrical current to generate a magnetic field w
hile a bar magnet already
has a magnetic field.

6.1 Discuss the dangers of an electric shock from both a 240 volt AC mains supply and various
DC voltages, from appliances, on the muscles of the body.

The higher the voltage the more severe the shock. The

current that flows across the heart is
the most dangerous and can cause fibrillation which causes the heart's muscle to oscillate
rapidly screwing up the normal process. Alternating current can cause fibrillation while DC
does not. Most dangerous electr
ocution is hand to hand or hand to opposite foot as the
current passes through the heart. Foot to foot is least dangerous. The dryness of the skin
determines resistance and can reduce the voltage or severity, however wet skin due to sweat
lowers this dra
matically.

6.2 Describe the functions of circuit breakers, fuses, earthing, double insulation and other
safety devices in the home.

These devices prevent overloading of a circuit and thus prevent fires from overheating, or
damage to the device. Earthing i
s used so that if a person touches the object that is not
earthed they will be electrocuted.

The World Communicates

1.1 Describe the energy transformations required in one of the following: mobile telephone,
fax/modem, radio and television

Mobile telephon
e: Sound energy
-

transformed to electrical energy
-

microwaves
-

electrical
energy
-

sound energy

1.2 Describe waves as a transfer of energy disturbance that may occur in one, two or three
dimensions, depending on the nature of the wave and the medium

A wave
is a carrier of energy through the motion of particles. Wave down a slinky (one), pebble
dropped in water (two), sound emitted from a speaker (three)

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Physics Revision
Notes

1.3 Identify that mechanical waves require a medium for propagation while electromagnetic
waves do not

Me
chanical waves require a medium while an electromagnetic does not, sound cannot travel
through a vacuum, but light can.

1.4 Define and apply he following terms to the wave model: medium, displacement,
amplitude, period, compression, rarefaction, crest,
trough, transverse waves, longitudinal
waves, frequency, wavelength, velocity

Medium
-

the material the wave is travelling through, displacement
-

distance a particle is away
from the equilibrium, amplitude
-

the maximum displacement of the particle, period
-

the time it
takes for one wave to pass through a fixed point, compression
-

areas in a longitudinal wave
where particles are compressed, rarefactions
-

areas in a longitudinal wave that are not
compressed, crest
-

highest part of a wave, trough
-

lowest point
of a wave, transverse waves
-

the direction of particle motion is perpendicular to the direction of wave propagation,
longitudinal waves
-

the direction of particle motion is parallel to the direction of wave
propagation, frequency
-

the number of waves that
pass through a fixed point in one second,
wavelength
-

distance between two adjacent points on a wave, velocity
-

the speed of a wave in
metres per second

1.5 Describe the relationship between particle motion and the direction of energy
propagation in trans
verse and longitudinal waves

Transverse
-

direction of particle motion is perpendicular to direction of wave propagation

Longitudinal
-

direction of particle motion is parallel to direction of wave propagation

1.6 Quantify the relationship between velocity,
frequency and wavelength for a wave
(velocity= frequency x wavelength)

Velocity is directly proportional to frequency and wavelength, velocity= frequency x wavelength

2.1 Identify that sound waves are vibrations or oscillations of particles in a medium

S
ound waves are waves that transmit energy through vibrations/ oscillation of particles in a
medium

2.2 Relate compressions and rarefactions of sound waves to the crests and troughs of
transverse waves used to represent them

The middle of a compression equa
tes to a crest and the middle of a rarefaction equates to a
trough

2.3 Explain qualitatively that pitch is related to frequency and volume to amplitude of sound
waves

The higher the pitch, the higher the frequency, while the higher the volume, the larger t
he
amplitude and vice versa

2.4 Explain an echo as a reflection of a sound wave

An echo is a reflection of a sound wave of a surface, where the wave is reflected off the surface,
resulting in an echo

2.5 Describe the principle of superposition and compare
the resulting waves to the original
waves in sound

Superposition is when two waves are in phase and for a brief moment, when they collide the
resulting wave doubles, then returns to normal. If the same happens for two waves out of
phase, then they cancel
each other out.

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3.1 Describe electromagnetic waves in terms of their speed in space and their lack of
requirement of a medium for propagation

All electromagnetic waves travel at the speed of light which is 3.0x 10^8 metres per second. All
can travel thr
ough a vacuum as they are not mechanical waves.

3.2 Identify the electromagnetic wavebands filtered out by the atmosphere, especially UV, X
-
rays and gamma rays

UV, X
-
rays and gamma rays, in particular waves of high frequency get filtered out by the
atmosph
ere

3.3 Identify methods for the detection of various wavebands in the electromagnetic spectrum

Communication technology, machines

3.4 Explain the relationship between the intensity of electromagnetic radiation and distance
from a source is an example of t
he inverse square law.

For every metre you stand back from a source, the inverse square is the drop in radiation

3.5 Outline how the modulation of amplitude or frequency of visible light, microwaves, and
or radio waves can be used to transmit information

AM and FM use amplitude and frequency to transmit information

3.6 Discuss problems produced by the limited range of the electromagnetic spectrum
available for communication purposes.

Not all EM waves can be used for communication, waves carry varying amoun
ts of data with
other problems like range, security and interference.

4.1 Describe and apply the law of reflection and explain the effects of reflection from a plane
surface on waves

Law of reflection, angle of incidence = angle of reflection

4.2 Describ
e ways in which applications of reflection of light, radio waves and microwaves
have assisted in information transfer

Fibre optics, radio, mobile phones

4.3 Describe one application of reflection for each of the following: plane surfaces, concave
surfaces,

convex surfaces, radio waves and being reflected by the ionosphere.

Mirrors, headlights, safety mirrors, long range transmission of AM waves

4.4 Explain that refraction is related to the velocities of a wave in different media and outline
how this may r
esult in the bending of a wavefront

The velocity of light slows down as it enters a new medium, causing the wave to bend as one
side slows down

4.5 Define refractive index in terms of changes in the velocity of a wave in passing from one
medium to another

A ratio of the speeds or sin angles of medium

4.6 Define Snell's Law

Velocity of light over velocity of material= sin (angle of incidence) over sin (angle of refraction)

4.7 Identify the conditions necessary for total internal reflection with reference to

the critical
angle

Total internal reflection occurs when angle of incidence is greater than critical angle, critical
angle occurs when angle of refraction is 90 degrees

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4.8 Outline how total internal reflection is used in optical fibres.

The light transfe
rs information which is continuously reflected through total internal reflection

Cosmic Engine

1.1 Outline the historical development of models of the Universe from the time of Aristotle to
the time of Newton

Aristotle
-

developed geocentric model because

it was common sense that the Earth was fixed
and not moving

Aristarchus
-

proposed heliocentric model

Ptolemy
-

added epicycles to account for retrograde motion and varying brightness of planets,
good predictions

Copernicus
-

developed heliocentric model

Galileo
-

proved the Copernican model through the telescope. Looked at phases of Venus and
moons of Jupiter.

Brahe
-

had a mixture of geocentric and heliocentric model. Made accurate predictions

Kepler
-

Brahe's assistant, developed his three laws

Newton
-

U
niversal Gravitational Law, the force between any mass in the universe

2.1 Outline the discovery of the expansion of the Universe by Hubble, following its earlier
prediction by Friedmann

Friedmann proved Einstein was wrong, the universe was expanding.
Hubble discovered red
shift implying that everything was moving away from everything else. Hence it was an
expanding universe.

2.2 Describe the transformation of radiation into matter which followed the Big Bang.

Radiation cooled down to form quarks and t
hen atoms, which then formed matter

2.4 Identify that Einstein described the equivalence of energy and mass

E= mc2 which says that energy can be converted to mass and vice versa.

2.5 Outline how the accretion of galaxies and stars occurred through, expansi
on and cooling
of the Universe, subsequent loss of particle kinetic energy, gravitational attraction between
particles, lumpiness of the gas cloud that then allows gravitational collapse

The Universe expanded and then cooled, allowing radiation to form par
ticles, which then
cooled. Over time it slowed down to clump together, forming gravitational attraction, these
centre of gravity formed gas clouds which got so hot, nuclear fusion occurred, causing stars to
form and hence galaxies formed through accretion
.

3.1 Define the relationship between the temperature of a body and the dominant wavelength
of the radiation emitted from that body

A body emits a certain wavelength (which is dominant that defines its colour). The hotter a
body, the more shifted the sp
ectrum to the left. A black body absorbs all radiation and emits
EMR

3.2 Identify that the surface temperature of a star is related to its colour

Hotter a star, more blue, white, while a cooler star is more orange red.

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Physics Revision
Notes

3.3 Describe a Hertzsprung
-

Russel
diagram as the graph of a star's luminosity against its
colour or surface temperature

In the middle there is the main sequence stars, with giants and supergiants above the
sequence, while white dwarfs are below the main sequence.

3.4 Identify energy source
s characteristic of each star group, including Main Sequence, red
giants and white dwarfs

Main Sequence, usually yellow in the colour and medium sized, red giants cool but huge stars
and are very luminous and white dwarfs are small but very hot, not lumino
us.

4.1 Identify that energy may be released from the nuclei of atoms

Energy release from the nuclei of atoms can be in one of three forms of radiation, alpha, beta
or gamma

4.2 Describe the nature of emissions from the nuclei of atoms as radiation of al
pha and beta
particles and gamma rays in terms of ionising power, penetrating power, effects of magnetic
field, effect of electric field

Alpha

Beta

Gamma

Nature

Helium nucleus

Electron

Ionising Power

High

Medium

Low

Penetration

Low

Medium

High

Magnetic Field

Moderate

Highly affected

Not affected

Electric Field

Moderate

Highly affected

Not affected

4.3 Describe the particulate nature of the solar wind

The solar wind is made of hot plasma, which consists of ions,
protons and electrons. Travels at
400
-
500 km/h

4.4 Outline the cyclic nature of sunspot activity and its impact on Earth through solar winds

Sunspot activity is cyclic and peaks every 11 years, with sunspots, flares and coronal mass
injections increasing
-

which disrupt electromagnetic communication and electrical grids.

4.5 Describe sunspots as representing regions of strong magnetic activity and lower
temperature.

Sunspots are regions on the surface of the sun that have an intense magnetic activity and lo
wer
temperature. They form due to the locations of disturbances in the magnetic field lines of the
Sun's surface.