Particles Quantum Phenomena and Electricity 4 Fundamental Forces

Particles, Quantum Phenomena and Electricity

4 Fundamental Forces n n Gravity Electromagnetic Weak nuclear Strong nuclear Ø Ø 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 Phenomena Annihilation - 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 Families Leptons – Fundamental particles Leptons = Lepton No. of +1 Anti-leptons = Lepton No. of -1 Not a Lepton = Lepton No. of 0

Particle Families Hadrons – 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 Diagrams EM Interaction

Feynmann Diagrams Weak Interaction (Beta minus)

Feynmann Diagrams Weak Interaction (Beta plus)

Feynmann Diagrams Weak Interaction (Electron capture)

Feynmann Diagrams Weak Interaction (Electron-proton collision)

β- (neutron) Decay The quark structure of the neutron is udd In β- decay a down quark changes to an up quark. uud = +2/3 -1/3 = 1 The neutron (Q = 0) has changed into a proton (Q = 1). neutron (udd) → proton (uud)

β+ (proton) Decay 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 1 Volt.

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 wave nature of particles. de. Broglie Wavelength,

Series circuits: n n Current same at all points – it is a continuous flow. Voltage shared between components. 24

Parallel Circuits n n Voltage same across branches as that of power source. Current splits between branches (splits and rejoins at junctions). 25

Cells in Series and Parallel

Using Ammeters n n n Ammeters measure the current flowing through themselves. Ammeters are placed in series. The ideal ammeter ought to have zero resistance.

Using Voltmeters n n n 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!

Resistors in Parallel

Resistor Combinations

Potential Dividers What is the p. d. across each of the two resistors? 12 V across each as they are equal resistance

Potential Dividers What is the p. d. across each branch? 3. 0 V

Potential Dividers What is the p. d. across the whole of the upper branch? 6. 0 V What is the p. d. across the lower branch? 6. 0 V What is the p. d. across each of the resistors in the upper branch? 3. 0 V

Potential Dividers What is the potential at X when thermistor has a resistance of 1000Ω? This is the p. d. across thermistor, the potential at X is 12 -11. 7=0. 3 V

Potential Dividers What is the potential at X when the LDR has a resistance of 5000Ω? 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.

Superconductivity Certain 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 • 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

Oscilloscope n n 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 10 ms / division and the y-gain is set at 100 m. V / division T=40 x 10 -3 s f=1/T=25 Hz Peak Voltage = 1. 5 x 100 m. V = 150 m. V