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Revision:AQA A Particle Physics

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[TSR Wiki]] > Study Help > Subjects and Revision > Revision Notes > Physics > A Level

Particle Physics


Contents

The atom and the nucleus

An atom consists of a nucleus which is orbited by electrons in outer shells known as electron shells.

The nucleus consists of protons and neutrons,these are known as nucleons.


\begin{tabular}{ || 1 | 2 | 3 | 4 | 5 ||} \hline $Particle$ & $Relative \; Charge$ & $Actual \; Charge /C$ & $Relative \; Mass$ & $Actual \; Mass /kg$ \\ \hline $Proton$ & 1 & 1.60E^{-19} & 1 & 1.67E^{-27}\\ $Neutron$ & 0 & 0 & 1 & 1.67E^{-27}\\ $Electron$ & 1 & -1.60E^{-19} & 1/1840 & 9.11E^{-31} \\ \hline \end{tabular}

Charge

Charge cannot be destroyed or created it in conserved.

It is also quantised - a quanta of charge is the smallest amount of charge possible and is equal to the charge of the proton or electron, 1.60E^{-19} C

Notation

^{Z}_{A}X


Z = Atomic mass ie. the number of protons and neutrons in the nucleus

A = Atomic number/proton number ie. number of protons in the nucleus.

The atomic number controls of the chemical properties and gives the type of chemical element.

Isotopes and Ions

Ions are CHARGED particles usually because of the loss or gain of an electron.

eg.

^{27}_{13}Al^{+}


P = 13

e = 12

n = 14


The + shows the particle is charged and what type of charge it has. In this case as the aluminium (Al) is missing an electron it has a positive charge as the atom contains more protons than electrons.


Isotopes are elements which contain the same amount of protons, same atomic number but have different amounts of neutrons in their nucleus.

Isotopes of the same element have the same chemical properties.

Charge to Mass Ratio

\frac {Charge}{Mass} & = & \frac {Q}{m}

Very easy to calculate lets take for example the charge to mass ratio for carbon 12.


^{12}_{6}C

We have 6 protons and 12 nucleons overall so:

\frac {Q}{M} & = & \frac {6 \times (1.60E^{-19})}{12 \times (1.67E^{-27})} & = & 4.79E^{7} CKg^{-1}


Mass-Energy equivalence and MeV

Mass-Energy equivalence

E=MC^2

E = energy

M = mass

C = speed of light, 3.0E^8ms^{-1}

Although for the AS you don't ever need to use the above equation you do need to know that is shows that all mass has an equivalent energy.


Mass of electron: M_e &=& 9.11E^{-31}kg

It's equivalent energy:

E =MC^2 & =& (9.11E^{-31}) \times (3.00E^8)^2

= 8.20E^{-14} J


Now these masses are called REST MASS because as the particles get closer to the speed of light their mass increases.

Also because mass has an equivalent energy as we have just shown we can use either rest mass or rest energies for a particle.

MeV

The electron volt, eV, is a unit of energy (a very small unit of energy)

1 eV = charge of an electron x 1 volt.

This is because rearranging the defintion of the Volt from V= \frac {E}{Q} to E = QV allows us to define a unit of energy for the electron.

1eV = 1.60E^{-19}J

so 1eV is a very small amount of energy.

1MeV is 1 mega electron volt and is = 10^6 x 1.60E^{-19}


1MeV = 1.60E^{-13}J


Calculating Rest energy in MeV


from joules to MeV:


\frac {Energy\; in\; joules}{1MeV}


from MeV to joules:


E\;in\;MeV \times 1MeV


ie. Rest energy of an electron = = 8.20E^{-14} J


\frac {(8.20E^{-14})}{(1.60E^{-13})}&=&0.51MeV

Thomsons "Plum Pudding" model

Rutherfords Alpha Particle Experiment

comments

AQA A AS Physics Module 1 Not complete will add images and finish sections.


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