Prelim Physics Notes

8/8/2019 Prelim Physics Notes

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End of Course Exam NotesP H Y S I C S

Scalar Quantities are quantities specified by size or magnitude but not defined notdirectionVector Quantities are quantities that are defined by direction as well as sizeVectors can be added to determine displacement using trignometry

MOTIONObjects can move without effective force acting on them

Distance is measure of total length of the path take during the motion of an objectDisplacement is measure of change in position of an object

Speed is measure of the rate at which an object moves over a distance Instantaneous Speed is speed of at a particular instant of time

Velocity is defined by speed and direction of a moving object

Velocity is relative to the observer who is measuring the velocity

Negative velocity is going backwards

Instantaneous Velocity is velocity at a particular instant of time if averagevelocity is constant the instantaneous velocity is the same

Speed formulas

Speed= =

Velocity=

Instantaneous speed =

Average speed = =

Acceleration is the rate at which an object changes its velocity

Area under graphs in velocity time graphs are used to determine distance

travelled

Constant Acceleration Formulas

a = acceleration

u = initial velocity

v = final velocity


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End of Course Exam Notes

t = time

s = displacement

FORCE AND NEWTONS LAWSAcceleration of force of gravity = 9.8m/s/s

Weight = mass force of gravity W=mg

Newtons 3 Laws of motion

1. A body persists its state of rest or of uniform motion unless acted upon by

an external unbalanced force The law of Inertia: The inertia of an object

is it tendency to resist changes in motion/velocity, it is not a force but

a property of all objects

2. F = ma ; force = mass acceleration or a ; F(newtons) =

m(kgs)a(m/s/s)

3. To every force there is an equal and opposite force When Object A exerts

a force (action) on object B, object B simultaneously exerts the equal force

(reaction) on object A, but in the opposite direction.

Forces on rolling car

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Momentum

Known as quantity of motionMeasure of how hard it is to stop or move an object or measure of how hard it is tochange an objects velocity

Momentum = mass velocity ;

Total Final momentum = total initial momentum (law of conservation of

momentum)

Multiple bodies

When multiple bodies are attached by string etc. the accel. Of entire system can

be determined and using this it can be used in F=ma to determine the force acting

on each body.

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MECHANICAL INTERACTIONSLaw of conservation of momentum

When objects collide/interact Momentum is always conserved

Total initial momentum = total final momentum

Momentum is vectorIn collisions:

Momentum is always conserved

KE is conserved in elastic (bouncy collisions)

KE not conserved in inelastic collisions

Total energy is always conserved KE is converted into other forms of energy

Kinetic Energy

The energy of moving objectsScalar Quantity

Change in KE Net Force acting on object

KE

Collisions (Interaction)

Some Kinetic energy is lost and changed into:

Potential energy

Sound energy

Thermal energy

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Impulse

Impulse is the change in momentum; SN or kg m/s

In a graph of force vs. time the impulse can be determined from area under graph

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ELECTRICITYElectrical charges are caused by an excess or deficiency of electrons

A deficiency is a + charge

An excess is a charge

Like charges repel

Unlike charges attract

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Objects that become charged because of the influence of other charged objects

are called induced dipoles.

Test charges are always positive

Calculating force caused by charges

K =

Q = charge on object 1 (coulombs)

q = charge on object 2 (coulombs)

d = distance (metres)

f = force (Newtons)

Coulombs

1 coulomb = excess or deficiency of electrons

1 Micro coulomb (mc) =

1 Nano Coulomb (nc) =

1 pico coulomb (pc) =

Charge on 1 electron = C

Electric Field Strength (only for spherical objects)

Units of E : Newtons per coulomb N/C

ELECTRICAL CIRCUITSBatteries push electron they are electron pumpsElectrical potential energy difference =

=work done by battery

A 1 volt battery does 1 joule of work to move 1 coulomb from one end to other orgives 1coulomb an electrical PE of 1Joule

1V = 1 Joule / coulomb

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Voltmeters and Ammeters

Voltmeters measures power supplied when connected across power supplyMeasures electrical potential lost when connected to other parts of a CircuitAlways set up in parallel with the part of the circuit being testedResistance

Resistance is ohms law; measured in ohmsType equation here.

A = cross section areaT = temperaturel = lengthR = ResistanceI = Current (amperes)V = Voltage (V)const = Resistivity (a property of the metal that makes up the wire)

A short circuit is where there is little to no resistance in a circuittherefore a huge current travels causing conductor to heat up

Electrical Power

Power = rate of which work is doneOrPower = rate at which one form of energy is transformed into another form of energyMeasure in Joules/Second or W (Watt)

1Kwh = 1 kilowatt hourIs electrical energy used by 1kw electric device running for 1 hour

WAVESWavelength is smallest distance between 2 crests or troughsFrequency is the number of crests going past a single point in one second or thenumber of complete cycles of any point on the medium per secondPeriod is the shortest time for 1 point on the wave to return to its original position orthe time for 1 wavelength to pass a single pointAmplitude is the height of each wave or maximum distance theParticles move from their original position also determines theVolume of sound waves

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frequency

wavelength

V velocity

In waves on springsV (velocity) depends on tension mass/meter

(in springs)

Waves can superimpose (stack up) to create bigger waves

Beats are loud soft cycles caused by the superposition of 2 sound waves of

slightly different frequencies.

Waves can bounce and transfer from one medium to another

Changing mediums

In particular mediums (velocity) is constant and

When waves pass from one medium to another (frequency) remains constant and

Particle motion in waves

In the middle of a rarefaction or compression the particles are in theirundisturbed state

Particle in rarefaction is moving backwards at max speed

Particle in a compression is moving forward at max speed

ELECTROMAGNETIC RADIATIONElectromagnetic radiation can refract, reflect and be absorbed.

RefractionWhen a wave moves from a fast (less dense) medium to a slow (denser) medium itbends towards the normal.

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Refractive index

Inverse square law

I (intensity)d (distance)

Critical AnglesThe angle of incidence that results in an angle of refraction equaling 90 degrees is thecritical angleIf the angle if incidence exceeds this angle the light beam will reflect instead ofrefract.Critical angle is influenced by refractive index

If

Total internal reflection

Total internal reflection in optic fibers2 (outer layer)1(inner)

Antinodal lineLine where waves from two sources superimpose to form the a line of greatest amplitude

COSMIC ENGINE1 Solar day time form the sun is due north to the next time the sun is due northSidereal day time from the time you face the stars to the next time you face thesame stars

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If

Partial refraction partial internal


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Approx 360 degree revolution1 Sidereal day is 4 minutes shorter than a solar dayNumber of sidereal days = number of solar days + 1Retrograde motion back and forth motion of planetsNorth celestial pole the pole of the Celestial sphere directly up from the NorthPole

South celestial pole the pole of the Celestial sphere directly up from South PoleCelestial Equator - Equator or the celestial sphereEcliptic the path that the sun seems to follow in the skyTycho BraheObserved planets with accuracy of 8 minutes

Keplers laws1. Law of ellipses: each planet moves in an ellipse with the sun at one focus.2.

Law of areas: the area swept out by a planet as it orbits the sun is proportionalto the time taken or i.e. the closer they are to the sun the faster they travel

along their orbit

3. Law of periods

Acceleration of circular motiona (acceleration)v (speed of orbiting object)d (distance from centre)

Gravitation forceG (gravitation constant) =

M (mass of object 1)m (mass of object 2)

Acceleration of gravity

Brightness of stars

Hertzsprung-Russel diagram for classifying star clusters

Using v-filters (allows visible light through) and b-filter (colors that arent visible)Color index of a star determined by subtracting visual magnitude from bluemagnitudeAbsolute brightness found by comparing apparent brightness and distance

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Spectra

The wavelengths of light emitted by certain atoms when energy is applied to them

Spectra can be detected by a spectroscopeUsed as evidence in determining temperature of stars.ExamplesSpectra of Ionised helium = mega hotSpectra of ionized calcium = hotSpectra of calcium = cooler

Doppler Effect

Effect of the distortion of light waves due to the movement of observation point andsourceNo color change BUT all spectra lines are shifted

Majority of stars are red shifted or majority of spectra lines are shifted towards the redspectrum of light

Hertsprung-Russel diagrams

Is scatter graph of stars showing relationships between absolutemagnitude/luminosity , spectral types/classifications and effectivetemperature.

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Main sequence fuse hydrogen in core to for helium

Red giants are super hot at core and fuse helium into carbon and hydrogen fusion in

outercore

Expanding universe

Edwin Hubble (1920s)Measured:

1. Distance to galaxies2. Doppler shift of galaxies :

Found speed of galaxies

Galaxies were moving away from each other

Concluded Universe is expanding

Hubbles law

Galaxies closer together in past

GenesisNothing

BIG BANG!

Quarks + electrons

Atoms (H + He)

Gas clouds

Stars

Gas

Evidence for BIG BANG1. Hubbles law > expanding universe2. Cosmic background radiation3. Observation of galaxies in distant past

Cosmic background radiation is the EM energy that was not converted into matterduring BIG BANG , emanates from all of universe

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Galaxies


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Was discovered as a constant noise picked up on satellite radios, it was samefrequency from all directions

RADIATION

particles: Nucleus of a helium atom

2 units of positive charge

Interacts strongly with matter can ionize other atoms

Rapidly slowed because of these interactions

Weakly penetrating

particles: Fast moving Negatively charged electron

Can go through atoms before ionization occurs

Strongly penetrating

rays:

High frequency EM radiation

No charge

Can penetrate up to several centimeters of lead

Low inonisation

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Prelim Physics Notes