Wave model of light ____________________________________

Diffraction – The bending of a wave around a barrier, obstacle or through a single slit

Path difference (PD) – Difference in length from a point in an interference pattern to the source

In phase – sources produce waves at the same freq where a crest meets a crest and a trough meets and trough

Constructive Interference– addition of amplitudes arriving in phase. Coherent has constant phase difference,

Destructive Interference – Crest meets a trough, amplitudes cancel

Antinode – constructive interference location Node – Destructive interference location

Antinodes: pd = nλNodes:pd= (n – 0.5)λ

Centre antinode is the brightest because I ∝ 1D2

Intensity is proportional to amplitude of wave

Fringe spacing (w), Distance from screen (D), slit width (s)

w=2Ds

Increasing D = decreasing intensity, increasing fringe spacing

Diffraction ∝ λS

- Increasing wavelength of light used

increases diffraction and hence w (fringe spacing)

λS≥ 1 means significant diffraction

Photoelectric effect____________________________________ Photocurrent –current induced by action of light Photoelectron – electron emitted from substance illuminated

by EMR

Ek=12

mv2 = Stopping voltage (J)

Stopping voltage ∝ (max speed)2 of fastest electrons (v2)

Varying Intensity of incident light More intensity (Wm-2) = greater photocurrent because more

photons means more electrons can be ejected every second

Power output of light: P= ΔJt

= Δnh ft

Planck’s Constant – h = 6.63 x 10 -34 Js/= 4.14 x 10 -15 eV __ 1eV (1.6 x 10-19J )–Eng gained by electron after it is moved by 1V pd

[1] eVto J(× by 1.6 x 10-19J) [2] J to eV (÷ by 1.6 x 10-19J)

E(J)= h(Js) f(Hz) = ∙hcλ

Planck’s experiments suggests light

sources do not emit continuous waves of light by instead, discrete bundled particles of eng called photons. Planck suggested: One photon can interact with one electron at any moment Photons deliver all their eng to electron upon interaction Total eng of light beam = number of photons (n) x hfWork function (W) – minimum eng (J) required for an electron to escape from an atom (W = h fo)Threshold Freq (fo) – Minimum freq at which photoelectric effect starts to occur (specific to different atoms)When a light of freq f is shone on an atom: h f = W + Ek

Therefore:12

m(vmax)2 = h f – W

Einstein’s relationship postulated that light travelled in discrete packets of energy (quanta: hf) and defined intensity as the number of photons, rather than the amplitude/energy of a waveIf hf> W, left over eng. given off as Kinetic eng (Ek)Eng – freq graphs_______________________________

Matter waves_________________________________________

Compton’s relationship:P=hλ=hf

c= Energy

cOnly applies to objects with no mass, p = momentum of photonDe Broglie replaced p with mv and postulated that matter had wavelengths as well

Derived relationships: ¿hmv

= h√2m Ek

, Since: EK = 12

mv2

De Broglie found that the diffraction pattern of x-rays was similar to those of electrons. Hence the wavelengths of electrons (particles) was similar to those of X-Rays (waves)Spectroscopes: Emission/Absorption Spectra________________Gas atoms absorb eng to promote their electrons to a higher eng state. As they fall back to ground level they release eng corresponding to different wavelengths of light.

Electrons can emit their eng in various combinations

Atoms emit the same amount of eng they absorb Atoms emit specific amounts of eng to promote their

electrons to excited states If an atom does not absorb enough eng to promote its

electrons to the next excitation state, it retains the eng as kinetic eng for its electrons

Electrons are unlikely to absorb eng in an excited state, hence eng required to promote an electron to a certain excited state is always relative to the ground levelFor example: 1st excitation state = 2eV, 2nd excitation state = 5ev Difference in eng levels = 3eVIf an atoms 3ev, electrons will only be promoted to the 1st excitation state and retain 1ev as Ek

It will NOT be promoted from the 1st excitation state to the 2nd

because it is unlikely excited atoms absorb eng; even if the eng absorbed is sufficient Difference in successive eng levels becomes smaller as you

move to highereng. level (n=0 and n=1 has the greatest difference)

Summary of experiments______________________________Flaws in wave model Did not explain why freq of light did not increase

photocurrent. Despite hypothesising that amplitude (intensity) of a wave

was related to a wave’s eng which should result in increase max Ek of electrons, did not explain why Max Ek changed with freq of incident light used.

Could not explain work function/ threshold freqSupport for the particle model = Flaws in wave model from photoelectric effect experimentParticle diffraction – Matter scatteringDavisson and Germer bombarded nickel crystals with electrons Speed of electrons known due to set accelerating voltage Maximum and minimum intensities were located at

different angles recorded by a detector (Similar to young’s double slit)

Electrons had undergone interference (once thought to be an exclusive wave property)Electrons fringe spacing and path difference used to calculate wavelength of electron (0.14nm) this value verified De Broglie’s wavelength formula:

λ= hmv using known velocity controlled by the

accelerating v & mass of an electron (9.11 x 10-31kg)Main relationships for the experiment:

[1] Ek∝Voltage [2] Ek = 12

mv2 [3]λ= hmv

Light and Matter

Wave Model Particle Model Light beams cross paths

undisturbed Refraction (Snell’s Law)

Inverse Sq. law (I ∝ 1D

) Linear Propagation Reflection

Linear PropagationReflection

Inverse Sq. law (I ∝ 1D2 )

Waves – transfer of eng without the net transfer of matter Mechanical waves – Requires a medium to propagate

through Wave Amplitude – maximum displacement a particle in a

mechanical wave has from its origin Periodic Wave – Source of disturbance undergoes

continual oscillation producing a constant waveLight Properties – Eng, no mass, no charge

n = 0

n = 1

n = 1

n = 1

n = 1

n = 2

n = 2

n = 2

Second minima Location of node

Swap terminals of battery (+ve terminal faces cathode) for -ve voltage at cathode (location of light) – This gives the max Ek

Monochromatic light used for this experiment

-ve terminal towards cathode:Accelerating voltage (voltage not impeding photocurrent)

-ve terminal towards cathode: Accelerating voltage (voltage not impeding photocurrent)Stopping voltage – How much work done by load to stop photoelectrons from being emitted ONLY affected by freq of incident light (greater freq. = higher

stopping voltage

Because absorption is a singular process and emission occurs in multiple steps there are more possible emission lines than absorption lines

Ionisation level –eng level where an electron has sufficient eng to overcome the electrostatic force binding it to the atomSpectroscope – qualitatively measures light emitted by electrons ROYGBIV. R greater wave than V, V higher freq than R

Emission spectra – bright bands on a backdrop of black corresponding to the eng released by electrons falling back to ground level(electron configuration which gives the atom the most stability and least eng)Absorption spectra – dark bands in the visible spectrum due to the absorption of specific wavelength of light by an atom

[1] Ek = hf – W [2] W = Y-Intercept[3] f – independent variable[4] h = gradient

[4] W (work on electron) = q (charge: 1.6x10-19C) x V (volts) = Ek

Double accelerating voltage:

2 xEk = Increases v by factor of √2 = Decreases wavelength

by factor of √2Absorption/emission spectraIncandescent lights – electricity sent through gas vapour to excite electrons – Electrons absorb eng releasing thermal eng as photons (Evidence for quantised discrete eng levels)Support for the dual nature of matter____________________ Discrete eng levels for particles (electrons) – Electrons

moved in waves inside their eng levels (quantised) Standing waves are the eng levels electrons exist within;

only certain λ of light will promote electrons (resonance)

Circumference of electron orbit = ¿2π r = nλ (standing

wave) forming a stable orbit

λ= hmv

∴n ∙ hmv

=2π r (n=1,2,3 ...)

n = 1 (ground level), n=2 (1st excitation state), etc.If an integral number of wavelengths cannot fit into the circumference of electron orbit, destructive interference occurs and the orbit (wavelength) is not an eng level

Left to right: n =3,4,5,6 EMF (source of potential difference) – PD is like a waterfall,

high potential eng at the top, low potential at the bottom. INSIDE a load (EMF) charges are separated via chemical reactions which give charges PD which allows them to flow to create a current when the circuit is completeVoltage (PD) – joules per coulomb

V = IR, in an open circuit R →∞, therefore V = 0

Power (P) = VI =V 2

R=E ( J )t

=I 2RSeries:Voltage: Vtotal = V1 + V2 + V3 + …Current: Itotal = I1 = I2 = I3 = …Resistance: Rtotal = R1 + R2 + R3 +…Parallel:Voltage: Vtotal = V1 = V2 = V3 = …Current: Itotal = I1 + I2 + I3 + …Resistance: 1/Rtotal = 1/R1 + 1/R2 + 1/R3 +…

Using multimeters ___________________________________Voltmeter – high resistance, hence no current flow across them, connected in parallel with component being measuredAmmeter – low resistance, connected in series with component current is being measured across

Voltage dividers_____________________________________ Voltage divider splits a voltage into smaller voltages to

supply other components in the circuit

Upper resistor – Resistor with higher resistance (lower resistor: vice versa)

Circuit components__________________________________

Thermistors -

LED– light emitting diodeAdvantages over globes:

1. Higher operation time/durability2. Consumes less power3. Faster response time4. Emits light at low voltages

Photodiodes – Used for detection of light; when sufficient light strikes eng. is dissipated into crystal lattice to allow electrons to flow. I=power/area (current from photodiode

∝ Light intensity) Placed in reverse bias: when light shines in diode, leakage current dramatically increased

Analog signal – A continually changing signal, uses continuous range of values to represent information

Digital signal – Discrete time signals generated by digital modulation, uses discrete/discontinuous values to represent information

Modulation – superimposing an information signal onto a carrier wave to transmit information. Change amplitude.

Carrier wave – High freq electromagnetic wave modulated in amplitude or frequency to convey a signalHigh freq carries more information (data density) and has a greater bandwidth with less interference

Demodulation – separating a modulated waveform into its carrier wave and information signal

Amplification and GainThere is a linear range, in which the amplifier circuit can amplify the voltage proportionately. Outside of this range, clipping or distortion occurs, where the output voltage is not proportional to the input voltage.

Biasing a transistor circuit means setting it up so that when there is no AC input, the output voltage is the value in the middle of its possible output range. This allows for the greatest possible variation in Vin, without distortion occurring. This mid-point is called the quiescent point or the bias voltage.

Voltage gain is the factor by which the input voltage is amplified to obtain the output voltage, multiply Vin/Vout by gain to find Vout/Vin:

Av = ΔVout/ ΔVin = gradient of the ΔVout vs. ΔVin graph.

If the voltage gain is negative, then the amplifier is described as inverting.

If the voltage gain is positive, then the amplifier is described as non-inverting.

*In parallel current splits to ratios.

Sound and sound systemsSound is a longitudinal wave with compressions and rarefactions (high/low pressure areas)

Wave equation v=fλf= 1T

Speed is independent of frequency only dependent on density of medium.Diffraction is the bending of waves as the pass the edge of an obstacle or through an aperture. Significant Diffraction occurs

when λw≥1Higher frequency diffracts less than lower.

Loudness of a sound depends on amplitude of the sound waves. Measured in phonsby comparing the sound with loudness of 1 kHz sound.

In string or open ended pipe(2nd harmonic=1st overtone)

f= nv2L

,n=1,2,3,4,5…

f 1: f 2: f 3…=1 :2: 3…In a pipe with 1 closed end (3rd harmonic, 1st overtone)

f= nv4 L

,n=1,3,5…

f 1: f 3: f 5…=1 :3 :5…

A rise in tone of one octave is equivalent to a doubling of the frequency.Sound systems Dynamic microphone: Sound moves the cone and the attached

coil of wire in a magnetic field to and fro. Electromagnetic induction produces an emf (signal) at the terminals of the coil.

Ribbon (or velocity) microphone: Air movement due to sound waves moves the metallic ribbon in a magnetic field. Electromagnetic induction generates emf between the ends of the ribbon.

Modulation_________________________________________ Attenuation – loss of power of a signal along a

communication channel. Low freq signals propagate through copper wiring with less attenuation than high freq signals

Bandwidth – amount of data transferred per second

Signal wave is reflected in the x axis and increased in frequencyTroughs in modulating wave (signal/information wave) represent nodes (zero values) in the modulated result

Light dependent resistors (LDR) – resistance decreases as light falls on it. Used to control light intensity from light emitting components

Negative Anode

Phototransistor- Base current comes from photons, more sensitive than photodiode but slower (~1µs). Time response is inversely related to gain which is usually 10 to 100. LED+LD (laser diode) -Forward biased emits light. Brightness due to current not voltage.

Electronics and Photonics Electric charge – Inherent property of electrons and

protons resulting in electric force between them (Force b/t charged particles)

Current – ANY movement of electric charge

I=Qt(Coulombs

sec)

First harmonic= Fundamental. Intensity is the rate at which the wave is carrying energy away from source through a given area. Decibel Scale logarithmic scale to compare loudness the way humans experience it. Doubling in Intensity is approximately 3dB. When two or more waves meet the resulting displacement at each point is the addition of the two displacements – Superposition.Resonance occurs when the forcing frequency equals the natural frequency of the object. Vibrate together in phase. Constructively add thus increase amplitude. Standing waves occur when the superposition of a wave creates stationary nodes and antinodes.

Condenser microphone: The back plate and the front metallic membrane form a capacitor (charged with a battery). Sound waves cause the membrane to vibrate and change the spacing between the plate and the membrane. This causes the output voltage (signal) to change.

In electret-condenser microphone a permanently charged electret material is used for the membrane, thus eliminating the need of a charging battery.

Crystal microphone: uses a thin strip of piezoelectric crystal attached to a diaphragm that is sent into vibration by sound waves, causing the crystal to deform and produce a voltage (signal).

Dynamic loudspeaker has the same basic construction as a dynamic microphone. The input signal changes the current in the coil and results in a varying magnetic force on the coil that is attached to the cone.

Enclosure formed by baffles: to prevent the sound from the back of the speaker cone cancelling the sound from the front because of destructive interference due to phase difference.A loudspeaker is omni-directional, (i.e. it radiates sound energy

spherically in all directions) when λw

>4

Intensity (Wm2 )∝ 1r2 I 1 r 12=I 2 r 22

dB=10 log Intensity10−12

Pressure node: Region where 0 pressure variation, open end of pipe due to inverted reflection.1violin, 80db, add 4 +10db, -3 db, 87db. 1 violin 65db, 10 violins 75db, 20 violins 78db.Same diffraction pattern, momentum (and wavelength) of the X-rays must have been the same as that of the electrons, P=mv

Effect of magnetic field on current______________________ RIGHT HAND GRIP RULE:

1. Thumb: direction of conventional current2. Fingers: direction of magnetic field

Solenoid – coil of wire in a cylindrical shape

In general: Anticlockwise circle (direction of current) - NORTH poleClockwise circle - SOUTH pole

Notation: Current into page / Current out of page

Magnetic Force and electric current_____________________ RIGHT HAND SLAP RULE –

1. Fingers: direction of magnetic field2. Palm: direction of magnetic force 3. Thumb: direction of conventional current

A magnetic force is exerted on positive charges when a current carrying wire is placed in an EXTERNAL magnetic field

The magnetic force is the force exerted on charges (work done to separate charges): i.e. if palm is facing upwards therefore POSITIVE CHARGES are pushed upwards

Magnetic force on wire = sum of individual forces on charges = nBIL sin(x)n – number of wiresB – magnetic field strength (T, Tesla)L – length of wire (m)

Parallel current carrying wires If the two currents are flowing in the same direction, they will attract each other.If the two currents are flowing in different directions, they will repel each other.

Electric motors______________________________________ Converts electrical energy to kinetic energy Maximal torque force when plane of the loop is parallel

with magnetic field Commutators –

Devices which reverse the direction of current when the plane of the loop becomes perpendicular to the magnetic field to ensure that the loop continues it rotation in one directionSplit ring for DC motors

To increase torque force of motor: increase size of loop, number of loops, strength of magnetic field OR current

Electromagnetic induction_____________________________Creation of current via changes in the magnetic field Flux (φ) – measure of total amount of magnetic field = BA

cos(x) in Tm2

where B = strength of magnetic field, A = area (m sq)

Induced EMF proportional to ∆φ∆ t

∆ φ=φ (Final )−φ ( Initial )

A Causes of change in flux∆ φ:

1. Change in B strength

Eddy currents – Currents produced in the conducting material by a change in flux (not necessarily a loop, i.e. iron core of a transformer which causes power loss)This problem can be produced by putting plastic laminations/layers in between the conducting material

Electric generators___________________________________ Converts kinetic energy into electrical energy

Uses FARADAY’s LAW Maximal flux when plane of the loop is perpendicular to

the magnetic field Minimal flux when plane of the loop is parallel to the

magnetic fieldChanging generators

1. Doubling rate of rotation/halving period/doubling frequency of rotation (revolutions per second)

= doubling ∆φ∆ t

= doubling emf

2. Doubling B = increase in flux3. Doubling A = increase in flux Summary of commutator uses:DC motors – split ringAC generators – SLIP ring, produces an AC voltage signalDC generations – split ring (produces pulsating DC voltage signal) i.e. |sin(x)| graph with a period that is half that of an AC generator’s voltage-time graph for particular frequency of rotation as well as same B and A values

Transformers – Peak, RMS, Peak to Peak_______________The transformer equation is: Np/Ns = Vp/Vs = Is/Ip, where p is primary and s is secondary.

The root mean square voltage (VRMS) is the value of an equivalent steady voltage (DC) supply which would provide the same power.

VRMS = Vp/√2. IRMS = Ip/√2. P = VRMS × IRMS = ½ × Vp × Ip = ½ × Pp.

Why do we use tranformers, you ask VCAA?

Well, because the power loss is proportional to the square of the current, it is important to reduce the current in long-distance transmission lines by using very high voltages. Hence a step up transformer is used at the start of the transmission wires and a step down transformer is used at the end of the transmission wires to reduce the current running along the wires.

More diagrams Use your right hand!

Electric power Magnetic fields – Property of space around magnets causing an

object in space to experience a force due only to the presence of the magnet (Vector quantity)

Magnets – Dipolar (two opposing poles), field lines never intersect (field lines run from N to S)Direction of field tangent to any point of the field lineField line density indicates relative field strength

Faraday’s Law_______________________________________

EMF = -N∆φ∆ t

, where N = number of loops in coil

Lenz’ Law___________________________________________ Any magnetic flux created by an induced current opposes

the change in flux which originally created itDiagram:

2. Change of loop size3. Change of velocity of magnet entering loopMagnetic field increase in strength as magnetic get closer to point of reference (i.e. a magnet at the centre of the loop will provide the biggest flux)

Summation of photoelectric effect (1905):The kinetic energy of photoelectrons is independent of the light intensity.If light was a wave, we would expect the energy of the incident light to be related to its amplitude or intensity, but ejected electrons seem to have the same amount of energy no matter what the intensity of the light is.Energy is related to frequencyThe photoelectric effect experiment suggests the existence of a threshold frequency. The particle model explains this though correlating the frequency of photons with its energy. E=hf, meaning that frequency is directly proportional to the energy of the photons. This explains why only certain photons of certain frequencies can dislodge electrons from the metal surface. The wave model does not explain this, as it suggests that photons of any frequency can free photoelectrons, given enough time.No time delayIf light was a wave, we would expect a time delay before any photoelectrons have absorbed enough energy to be ejected, especially at low intensities, but this is not observed. Photoelectrons are emitted instantaneously.IntensityWtf does intensity have to do with anything then? The intensity just gives an indication of the number of photons per unit area. Therefore, more photons means more photoelectrons are emitted, AT THE SAME ENERGY as if the intensity was any different. This can be observed by the fact that increasing the intensity increases the photoelectron current.

Young Double SlitExp:1801 - This experiment demonstrates that light is influenced by principles of interference and diffraction, both characteristics which can only be explained by a wave model of light. Bright bands are areas of constructive interference and dark bands are areas of destructive interference.Young’s experiment demonstrated an interference pattern of bright and dark bands formed by constructive and destructive interference. Since this is a wave phenomenon, Young concluded that light had a wave nature. Photoelectric effect: Electrons ejected range of energies. As the retarding voltage was increased, fewer electrons had sufficient energy to reach the collector so the current decreased. When the voltage reached stopping potential even

Faraday’s Law of Induction is a mathematical relationship between the rate of change of flux and the generated EMF (electromotive force). It is: Ε = -nΔΦ/Δt.

Lenz’s Law is a qualitative statement. It states that induced current in a loop will be in the direction so that the flux it creates will oppose the change in the flux that produced it. It is simply an alteration of the law of conservation of energy. OPPOSE CHANGES!

When graphing EMF from flux change, just graph the negative derivative. Pls don’t forget your methods/specialist maths.More important formulae: Ε = -nΔΦ/ΔtE= BlvΦ = BA (no n here people, don’t f%^& this up)F=qvBsinx

A Causes of change in flux∆ φ:

1. Change in B strength

Energy and Force – Total mechanical Energy = kinetic + potential energy.

E(Kinetic )=12mv2 (Elastic: Ekfinal=Ekinitial, if not

equal, inelastic as energy is to sound or heat etc. Momentum conserved for both)

U (gravity )=mgh (ONLY IFGRAVITY ISCONSTANT ) W=Fxcosθ

U (gravity )=12k x2

MOTION

v=u+at

x= t(u+v )2

x=ut+0.5a t2

x=vt−0.5a t 2

v2=u2+2ax

a=∆v∆ t

NEWTON’S LAWS1. Every object continues to be at rest, or continues with constant velocity, unless it experiences an unbalanced force (law of inertia) 2. F=ma The rate of change of momentum is directly proportional to the magnitude of the net force and is in the direction of the net force3. For every action there is an equal and opposite reaction. Action-reaction pairs act on different objects; forces of action-reaction pairs can’t be added together

Step up after generator before power lines, Step down at end of transmission lines. Step up increase RMS voltage to lower current and power loss. Because power transmitted as AC signals, we assume that values used to calculate power are RMS unless told otherwise. Thicker wires decrease resistance. FOR THE SAME POWER IN EQUATIONS WITH TRANSFORMERS, increasing transmission voltage, decrease current. Half Hz, double period, thus half emf. Max on flux graph goes to x intercept of emf. Cconstant current, constant magnetic flux.No change in flux, no voltage would be induced.

Graph Interpretation

X-axis Y-axis Area Under GradientExtension Force U(spring) SprConst

Time Velocity Displa Accel

Time Accele Velocity -

Time Net F Impulse -

Displac Force Work -

Distan F(gravity) E change

ACTION/REACTION Action/reaction forces: Always exist inpairs Are equal inmagnitude Actin oppositedirections If a ball is on the ground, it is NOT an action reaction as

all forces are acting on the ball. But if the ball is thrown to the ground, the ball acts on the ground and the ground acts on the earth so it IS an action reaction pair.

BANKED ROADS

nsinθ=mv2

r…1

ncosθ=mg…2

12=tanθ=v2/rg – Design speed

Relate angle to velocity and gravity

Total Centripetal acceleration = nsinθ+F ( friction ) cosθIgnore F (friction)cosθ

Increase the force towards the centre with a banked road so you can go at greater speeds as they give a greater centripetal acceleration. This is because mgcosθ=Acentripetal – Normal , Normal is larger now.

Force Normal > Force Weight (FN is hypotenuse when resolving forces). ONLY gravitational weight force and normal forces on diagram.

Since force centripetal is Nsinθ, larger the angle, larger the centripetal force.

PROJECTILE MOTION Only force on projectile is gravity. Air resistance is

opposite direction of motion.

↑v=u+at whichis up¿maxheight 0=usinθ−¿

t=usinθg

therfore total time=2usinθg

↑ x=vt−12a t 2

h=0−12

(−g )(usinθg )2

Weightlessness An object will experience apparent weightlessness when

falling with acceleration equal to gravitational field strength (Free fall towards earth). They feel weightless when Fnormal = 0.

Gravitational weight force is force by earth on you. Reaction force is force by surface on you.

mg−N=ma True weightlessness when g=0 N/kg usually in deep space. Fn>Fg, heavier. Fn<Fg, lighter.

Note: When an applied force opposing friction or gravity is doing work with no increase in speed of object then

P= Fx∆ t

=Faverage∗velocity average

TENSION Connected bodies.

T=m1×m2×gm1+m2

a= m1∗gm1+m2

Sample answer: What is the role of crumple zones in cars or tanbark in playground in reducing the ‘effect’ of a collision?If an object with a certain velocity is brought to rest, it will have a certain change in momentum that is constant for that particular collision. The average force exerted on the object, therefore, is dependent on the time of collision (F = I/t, since I is constant F ∝ 1/t). If the time is prolonged then the average force exerted would be less and consequently, less injuries would result from these collisions.

Sample answer: Apparent weightlessnessApparent weightlessness is achieved when an object falls with an acceleration equal to the gravitational field strength, as no normal reaction force is experienced. For example, astronauts in a satellite in stable orbit will feel weightless as the satellite is in constant free-fall.

Summation of photoelectric effect (1905):The kinetic energy of photoelectrons is independent of the light intensity.If light was a wave, we would expect the energy of the incident light to be related to its amplitude or intensity, but ejected electrons seem to have the same amount of energy no matter what the intensity of the light is.Energy is related to frequencyThe photoelectric effect experiment suggests the existence of a threshold frequency. The particle model explains this though correlating the frequency of photons with its energy. E=hf, meaning that frequency is directly proportional to the energy of the photons. This explains why only certain photons of certain frequencies can dislodge electrons from the metal surface. The wave model does not explain this, as it suggests that photons of any frequency can free photoelectrons, given enough time.No time delayIf light was a wave, we would expect a time delay before any photoelectrons have absorbed enough energy to be ejected, especially at low intensities, but this is not observed. Photoelectrons are emitted instantaneously.IntensityWtf does intensity have to do with anything then? The intensity just gives an indication of the number of photons per unit area. Therefore, more photons means more photoelectrons are emitted, AT THE SAME ENERGY as if the intensity was any different. This can be observed by the fact that increasing the intensity increases the photoelectron current.

Young Double SlitExp:1801 - This experiment demonstrates that light is influenced by principles of interference and diffraction, both characteristics which can only be explained by a wave model of light. Bright bands are areas of constructive interference and dark bands are areas of destructive interference.Young’s experiment demonstrated an interference pattern of bright and dark bands formed by constructive and destructive interference. Since this is a wave phenomenon, Young concluded that light had a wave nature. Photoelectric effect: Electrons ejected range of energies. As the retarding voltage was increased, fewer electrons had sufficient energy to reach the collector so the current decreased. When the voltage reached stopping potential even

CENTRIPETAL MOTION

a=4 π2 r

T= v2

r

F=4 π2mrT

=mv2

r Speed=Distance

time=2 πr

T

Don’t worryIkram, still have these just for you!g – gravitational field: use 10, not 9.8a – acceleration (ms-2)F – Force (Newtons)v – velocity (ms-1)M- central mass (kg)m – orbiting mass (kg)r – radius of orbit (m)T – periodof orbit (s)G - 6.67x10-11Nm2kg-2

o Momentum

E(Kinetic )=12mv2

p=mv