Particles, Quantum Phenomena and Electricity
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Transcript of Particles, Quantum Phenomena and Electricity
Particles, Quantum Phenomena
and Electricity
4 Fundamental Forces
Gravity Electromagnetic Weak nuclear Strong nuclear
gravitons photons W bosons (and Z boson) Pi mesons (pions)
Any particle with mass
Any charged particle
All leptons, baryons and mesons
Hadrons
Alpha Particle Scattering• Nucleus is tiny
• Nucleus is massive
• Nucleus is very dense
• Atom is mostly free space
Quantum PhenomenaAnnihilation- The conversion of mass to energy- 2 gamma ray photons released
Quantum Phenomena
Pair Production- The conversion of energy to mass- A gamma ray photon of sufficient
energy may decay into an electron and a positron
Particle FamiliesLeptons – Fundamental particles
Leptons = Lepton No. of +1 Anti-leptons = Lepton No. of -1
Not a Lepton = Lepton No. of 0
Particle FamiliesHadrons – Composed of quarks
Baryons = Baryon No. of +1 Anti-baryon = Baryon No. of -1
Not a Baryon = Baryon No. of 0 (Including mesons)
Particle Families
Some particles:
Feynmann DiagramsEM Interaction
Feynmann DiagramsWeak Interaction (Beta minus)
Feynmann DiagramsWeak Interaction (Beta plus)
Feynmann Diagrams Weak Interaction (Electron capture)
Feynmann Diagrams Weak Interaction (Electron-proton collision)
β- (neutron) Decay
eA
ZAZ YX 0
0011
The quark structure of the neutron is udd
In β- decay a down quark changes to an up quark.
uud = +2/3 +2/3 -1/3 = 1
The neutron (Q = 0) has changed into a proton (Q = 1).
neutron (udd) → proton (uud)
β+ (proton) Decay
eA
ZAZ YX 0
0011
In β+ decay an up quark in a proton changes to a down quark.
This only happens in proton-rich nuclei.
proton (uud) → neutron (udd)
Particle Interactions
The 4 quantities (Q, B, S and L) have to be the same after a reaction as they were before it occurred.
Important:Strangeness is only conserved in the strong and electromagnetic interactions.
The electronvolt is an amount of energy equal to the above value.
It is arrived at by applying the equation
E= QV to an electron accelerated by a p.d. of 1Volt.
J1.6x101eV 19
Photoelectric Effect
hf = φ + Ek (SI Units)
Energy Levels and electron excitation
E = hf
Fluorescent Tube
Wave-particle Duality
The Photoelectric Effect suggests the particle nature of light.
Electron diffraction suggests the wavenature of particles.
mv
hλ or
p
hλ
deBroglie Wavelength,
ItQ QVE
IVP
IRV
t
WP A
lR
ItVE
24
Series circuits:
Current same at all points – it is a continuous flow.
Voltage shared between components.
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Parallel Circuits
Voltage same across branches as that of power source.
Current splits between branches (splits and rejoins at junctions).
Cells in Series and Parallel
Using Ammeters
Ammeters measure the current flowing through themselves.
Ammeters are placed in series.
The ideal ammeter ought to have zero resistance.
Using Voltmeters
Voltmeters measure the voltage between two places.
This is also called potential difference. (The difference in the “push” between two places)
Voltmeters are placed in parallel.
I-V Characteristics
Thermistors – Resistance decreases as temperature increases
LDR – Resistance decreases as light intensity increases
Resistors in Series
Easy!
321 RRRR
Resistors in Parallel
321Parallel R1
R1
R1
R1
Resistor Combinations
30301
201
201
20RTotal 15
2
30
1
20
1
20
1
R
1
Parallel
7.5Ω215RParallel
57.5Ω30207.5RTotal
Potential Dividers
TotalV×R
R=V
Total
What is the p.d. across each of the two resistors?
12V across each as they are equal resistance
Potential Dividers
TotalV×R
R=V
Total
What is the p.d. across each branch?
3.0V
Potential Dividers
TotalV×R
R=V
Total
What is the p.d. across the whole of the upper branch?
6.0V
What is the p.d. across the lower branch?
6.0V
What is the p.d. across each of the resistors in the upper branch?
3.0V
Potential Dividers
TotalV×R
R=V
Total
What is the potential at X when the thermistor has a resistance of 1000Ω?
11.7V121030
1000V
This is the p.d. across the thermistor, the potential at X is 12-11.7=0.3V
Potential Dividers
What is the potential at X when the LDR has a resistance of 5000Ω?
TotalV×R
R=V
Total
11.9V125050
5000V
This is the p.d. across the LDR, in this case it is also the potential at X due to where the LDR is in the circuit.
SuperconductivityCertain materials have zero resistivity at and below a critical temperature which depends on the material.
There is a persistent current in the superconductor that causes a magnetic field to be set up that repels the magnetic field of the permanent magnet.
EMF and internal resistance
r)I(Rε
• The quantity of energy transferred to unit charge as it passes through the cell
• The p.d. across the cell when no current flows
• Energy is transferred in the cell due to the internal resistance
RMS Values
00
rms 0.707I2
II
00
rms 0.707V2
VV
Oscilloscope x-axis is called the timebase y-axis is the y-gain or input sensitivity (which represents
p.d.)Calculate the frequency and the amplitude of the signal shown if the timebase is set to 10ms / division and the y-gain is set at 100mV / divisionT=40x10-3s
f=1/T=25Hz
Peak Voltage = 2x100mV
= 200mV