Edexcel A-Level Physics Master Revision Guide

What are the two broad categories of all particles?

Hadrons and Leptons

What is a lepton?

A fundamental particle that cannot be broken down further (e.g. electron; muon; neutrino)

What lepton number do standard leptons have?

+1 (antiparticles have -1)

What is a hadron?

A non-fundamental particle composed of quarks

What are the two sub-groups of hadrons?

Baryons and Mesons

What is a baryon?

A particle made of three quarks (qqq) or three antiquarks

What baryon number do baryons and antibaryons have?

+1 for baryons; -1 for antibaryons

What is a meson?

A particle made of a quark-antiquark pair (q qbar) with baryon number 0

What is the electric charge of an up quark?

+2/3 e

What is the electric charge of a down quark?

-1/3 e

What is the electric charge of a strange quark?

-1/3 e

What is the strangeness of a strange quark?

-1

What is the strangeness of an anti-strange quark?

+1

What is the quark composition of a neutron?

udd (down down up)

What is the quark composition of a proton?

uud

What charge does a proton have based on its quarks?

+1e (2/3 + 2/3 - 1/3)

What charge does a neutron have based on its quarks?

0 (2/3 - 1/3 - 1/3)

What are pions?

Mesons that do not contain strange quarks

What are kaons?

Mesons that contain a strange or anti-strange quark

What exchange particle carries the electromagnetic force?

The virtual photon

What exchange particle carries gravity (theoretical)?

The graviton

What particles does the weak nuclear force affect?

Virtually all particles

What are the exchange particles of the weak nuclear force?

W+; W-; and Z0 bosons

What does the weak nuclear force do to quarks?

Causes flavour changes during weak interactions

What particles does the strong nuclear force affect?

Hadrons only

What is the exchange particle of the strong nuclear force?

The pion (or gluon)

Over what range does the strong nuclear force act?

About 3 to 4 fm

What happens to the strong force below 0.5 fm?

It becomes strongly repulsive to stop the nucleus collapsing

Which four quantities must be conserved in particle interactions?

Electric charge; baryon number; electron lepton number; muon lepton number

Describe beta-minus decay at the quark level

A down quark decays into an up quark; emitting an electron and an anti-electron neutrino; mediated by a W- boson

Describe beta-plus decay at the quark level

An up quark turns into a down quark; emitting a positron and an electron neutrino; mediated by a W+ boson

Describe electron capture

A proton captures an inner-shell electron; becoming a neutron and emitting an electron neutrino; mediated by a W+ boson

What is gamma radiation?

High-energy electromagnetic waves emitted directly by an excited nucleus with excess energy

What is an alpha particle?

A helium nucleus: two protons and two neutrons

What happens to atomic and mass number during alpha decay?

Atomic number decreases by 2; mass number decreases by 4

What is beta-minus radiation?

A fast-moving electron ejected from the nucleus when a neutron transforms into a proton

What happens to atomic and mass number during beta-minus decay?

Atomic number increases by 1; mass number stays the same

What happens during annihilation?

A particle and its antiparticle collide and all their mass converts into two photons travelling in opposite directions

What is the minimum photon energy formula for annihilation?

E_min = mc^2 = hf

What is pair production?

A single high-energy photon spontaneously converts into a particle-antiparticle pair

What is the minimum photon energy formula for pair production?

hf_min = 2mc^2

What is electric current?

The rate of flow of electric charge; I = Q/t

How is an ammeter connected to measure current?

In series

What is potential difference?

Energy transferred per unit charge between two points; V = E/Q

How is a voltmeter connected to measure potential difference?

In parallel across the component

State Ohm's Law

V = IR

Describe the I-V characteristic of an ohmic resistor

A straight line through the origin

Why does a filament lamp's resistance increase with current?

Increased collisions of electrons with lattice ions cause more vibration and heating; increasing resistance

How does a diode behave in forward vs reverse bias?

Very high resistance in reverse bias; resistance drops sharply above the threshold voltage (~1V) in forward bias

What is a superconductor?

A material with precisely zero electrical resistance below its critical temperature

Define resistivity

The resistance of a 1 m^3 cube of a material; measured in Ohm-metres

State the resistivity formula

rho = RA/L

How do you calculate cross-sectional area from wire diameter?

A = pi d^2 / 4

State Kirchhoff's First Law

The total current entering a junction equals the total current leaving it

State Kirchhoff's Second Law

In a closed loop; the sum of EMFs equals the sum of potential difference drops

In series circuits; how does current behave?

It is the same through all components

In series circuits; how does total resistance behave?

It is the sum of individual resistances

In parallel circuits; how does potential difference behave?

It is equal across every branch

In parallel circuits; how does total resistance behave?

It decreases as more branches are added (reciprocals add)

State the potential divider equation

V_out = V_in x (Rx / R_total)

How does an NTC thermistor's resistance change with temperature?

It decreases as temperature increases

How does an LDR's resistance change with light intensity?

It decreases as light intensity increases

State the three power equations

P = VI = I^2 R = V^2/R

What is the peak voltage of UK mains supply?

325 V

What is the RMS voltage of UK mains supply?

About 230 V

How is V_RMS related to V_peak?

V_RMS = V_peak / sqrt(2)

What is mean power in terms of peak power?

P_mean = P_peak / 2

What is EMF?

Total energy converted per unit charge by a source from chemical to electrical energy

What is internal resistance?

The inherent resistance inside a cell that causes lost volts (Ir)

State the EMF equation including internal resistance

EMF = V + Ir = I(R + r)

On a graph of terminal pd against current; what does the y-intercept represent?

The EMF

On a graph of terminal pd against current; what does the gradient magnitude represent?

The internal resistance r

Give an example of a scalar quantity

Distance; speed; mass; time; or energy

Give an example of a vector quantity

Displacement; velocity; acceleration; force; momentum; or weight

How do you add two perpendicular vectors?

Using Pythagoras' theorem and trigonometry

How do you resolve a force F at angle theta to the horizontal?

Horizontal component = F cos(theta); vertical component = F sin(theta)

State the formula for work done

W = F d cos(theta)

State the formula for gravitational potential energy

E_p = mgh

State the formula for kinetic energy

E_k = 1/2 m v^2

State the formula for power

P = W/t = Fv

State Newton's First Law

An object stays at rest or constant velocity unless acted on by a non-zero resultant force

State Newton's Second Law

F_net = ma (resultant force proportional to rate of change of momentum)

State Newton's Third Law

Every action force has an equal and opposite reaction force on a different body

On an inclined plane; what is the component of weight parallel to the ramp?

mg sin(theta)

On an inclined plane; what is the component of weight perpendicular to the ramp?

mg cos(theta)

List the four SUVAT equations

v = u + at; s = ut + 1/2 at^2; s = (u+v)t/2; v^2 = u^2 + 2as

For projectile motion; what is the horizontal acceleration?

Zero (constant horizontal velocity)

For projectile motion; what provides the vertical acceleration?

Gravity (-9.81 m/s^2)

Define linear momentum

p = mv (a vector quantity)

State the principle of conservation of momentum

Total momentum before equals total momentum after; provided no external forces act

What is the change in momentum when an object rebounds elastically off a wall?

Delta p = -2mu

What is conserved in an elastic collision?

Total kinetic energy

What happens to kinetic energy in an inelastic collision?

It is not conserved; some is lost as heat/sound/deformation

State the force-momentum relation

F = Delta p / Delta t

What does the area under a force-time graph represent?

Impulse (change in momentum)

State the fluid flow force formula

F = rho A v^2

Define a moment (torque)

F x d_perpendicular

State the principle of moments

Sum of clockwise moments about a pivot equals sum of anticlockwise moments

What are the two conditions for equilibrium?

Resultant force is zero; and resultant moment about any point is zero

What is a couple?

Two equal; opposite; parallel forces not acting along the same line; producing rotation without translation