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 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 +1Anti-leptons = Lepton No. of -1 Not a Lepton = Lepton No. of 0
Particle Families Hadrons – Composed of quarks Baryons = Baryon No. of +1Anti-baryon = Baryon No. of -1 Not a Baryon = Baryon No. of 0 (Including mesons)
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 +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 1Volt.
Potential Dividers What is the p.d. across each of the two resistors? 12V across each as they are equal resistance
Potential Dividers What is the p.d. across each branch? 3.0V
Potential Dividers 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 What is the potential at X when the thermistor has a resistance of 1000 Ω? 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 5000 Ω? 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
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 / division T=40x10 -3 s f=1/T=25Hz Peak Voltage = 1.5x100mV = 150mV