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.

25

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