Physics

Physics

1. SI units, prefixes and inaccuracies

   • Si units were assembled/created so that if scientists were to share their recent findings, then they'd have to use SI units so that other scientists know what calculations they are doing and what procedures they are going through
   • Prefixes are used to express a number to a certain power of 10 instead of writing the whole number full of 0s from start to end.
   • When measuring something with a measuring tape or a rule, and you decide to state the length, width, height a decimal, then you are starting to introduce inaccuracies into your working. So its best to avoid stating a measurement as a decimal and instead measuring the object with a smaller unit ('mm' instead of 'cm') or converting the measurement to a smaller unit.
   • Different types of prefixes
     • Kilo = 10^3
     • Giga = 10^9
     • Mega = 10^6
     • Tera = 10^12
     • Peta = 10^15
     • milli = 10^-3
     • micro = 10^-6
     • nano = 10^-9
     • pico = 10^-12
     • femto = 10^-15

2. Particles and specific charge

   • Specific charge is calculated by dividing charge (in coulombs) by mass (in kilograms). The specific charge is the ratio of the charge of the atom to its mass.
   • When asked what the nucleon number is, it is simply another name for the mass number.
   • Particle masses
     • Mass of proton and neutron is 1.67*10^-27 kg
     • Mass of an electron is 9.11*10^-31
   • Particle charges
     • Charge of a proton is +1.6*10^-19
     • Charge of an electron is -1.6*10^-19
     • A neutron doesn't have any charge since it's neutral
   • Anti-particles
     • For every particle, there is always a corresponding anti-particle. Anti-particles don't differ all that much from normal particles, they have the same mass and rest energy as normal particles however, they have opposite charges of their corresponding particles. For an example the anti-particle of an electron is a positron which has an opposite positive charge.
     • The corresponding anti-particles are as follows:
       • A positron is the corresponding anti-particle of an electron
       • An anti-proton is the corresponding anti-particle of a proton
       • An anti-neutron is the corresponding anti-particle of a neutron

3. Types of decay

   • Alpha decay is where an atom emits a helium atom (2 protons and 2 neutrons) from its nucleus. This mostly occurs with very big atoms (atoms that have more than 82 protons in the nucleus) because, the strong nuclear force is just not strong enough to keep these big particles together. So when an atom undergoes alpha decay, it emits an alpha particle (or a helium particle) which makes the old atom a new atom, so it changes element.
   • Beta decay is another type of decay where the atom emits a beta particle (an electron) and an anti-neutrino therefore once more the element changes. This mostly occurs in isotopes that are 'neutron rich' (when the amount of neutrons is far bigger than the amount of protons). The reason why the old atom changes into a new atom is because, the electron which was emitted, joins the other electrons orbiting the nucleus.
     • Beta decay can also be written as: n --> p + e- + Ve (anti-neutrino)

4. Photons

   • When discovered these waves were simply known as packets of electromagnetic energy.
     • If you want to find out the amount of energy a photon has then you'll simply need to use the 'E=hf' or the 'E=hc/lambda' formula.

5. Pair production and annhialation

   • Pair production is when two of the same types of particles collide at high speeds, causing the energy produced from the collision to convert into mass however, it'll only convert from energy to mass if there is enough energy in the first place. When the energy does convert into mass it'll always produce a particle and its corresponding anti-particle of the types of particles that collided. Photons can also perform pair production although it mostly occurs when the photon passes by a nucleus of an atom. When pair production occurs with photons, an electron and positron are created. To work out the minimum amount of energy created from pair production you would use the E(min) = 2E(o). So the minimum amount of energy needed for pair production to take place is double the rest energy of the particles being produced.
   • Annihilation is when a particle and an antiparticle of the same type of particle collide together which causes two photons to be given off. To work out the minimum of energy created by annihilation would be 'E(min) = E(o)' or in other words it'd be equal to the rest energy of the type of particle that was annhialated.

6. Classification of particles

   • Particles are classed into 2 groups; Hadrons and Leptons
     • Hadrons
       • Baryons
         • Baryons are affected by the strong nuclear force which separates them from leptons. Baryons have 3 quarks
           • There is also the baryon number which is always conserved in decay. All baryons have a number of +1, other types of particles have a baryon number of 0, and anti-baryons have a number of -1.
         • Protons and neutrons are an example of baryons
       • Messons
         • Messons are made up of a quark and anti-quark pair which are also affected by strong nuclear force.
         • Examples of messons are pions and kaons
     • Leptons
       • Leptons are separated from hadrons because, they aren't affected by the strong nuclear force however, they are affected by the electro magnetic force and weak interaction.

7. Quarks

   • Particles are made up of smaller particles called quarks, anti-particles are made of anti-quarks. There are 6 types of quarks however, you only need to remember 3 types.
     • The 3 types of quarks are the 'up' quark, the 'down' quark and the 'strange' quark.
       • 'up' quarks have a charge of +2/3
       • 'down' quarks have a charge of -1/3
       • 'strange' quarks have a charge of -1/3
     • As an example, protons (uud) and neutrons (udd) are made up of quarks

8. Further decay

   • Beta Minus decay
     • Beta minus decay is when a neutron decays into a proton, electron and an anti-neutrino
       • n --> p + e- + Ve (anti-neutrino)
   • Beta Plus Decay
     • Beta plus decay is when a proton decays into a neutron, positron and a neutrino
       • p --> n + e+ + Ve (neutrino)

9. Conservation

   • When particle interactions occur and decay occurs some things are conserved however, other aren't. An example of this is that the baryon and lepton number is conserved along with charge and energy. The only thing that isn't conserved is strangeness.

10. Feynman Diagrams

    • n --> p + e- + Ve (anti-neutrino)
    • p --> n + e+ + Ve (neutrino)
    • p + e- --> n + Ve (neutrino) W+
    • p + e- --> n + Ve (neutrino) W-
    • e- + e- --> e- + e-
    • p + p --> p + p

11. Photoelectric affect

    • The photoelectric effect explains how light is acting as a particle and not a wave. By using a gold leaf electroscope we can see that when a gold leaf is negatively charged (causing it to the repel from the metal next to it) UV light shines down onto the metal object causing the electrons to be liberated from the structure of the atom. However when a different type of light shines down (visible light for example) then nothing would happen because, the particle doesn't have enough energy to liberate the electron from its atom. If light was a wave then we'd be able to slowly build up that energy until the electron would have enough energy to be liberated from its atom however, as we see no matter how much visible light we bombard the metal, the electron wouldn't be liberated from its electron.
      • What determines if a particle has enough energy to liberate an electron from its atom is the threshold wavelength and the threshold frequency. If the energy of a particle is below the threshold wavelength or threshold frequency then the electron wouldn't be liberated from its atom.

12. Energy levels in atoms

    • When an atom is above its ground state, it has an energy level of 'n' (with the lowest energy level being 1 which is the ground state), we call this atom excited
      • When electrons move down an energy level they emit a photon which has a maximum amount of energy that it can carry. The amount of energy a photon carries depends on the energy level the electron has switched to
        • Change in energy in joules = Energy level changed to - original energy level = hf
    • Ionisation
      • Ionisation is when an electron is removed from an atom. The ionisation energy of an atom is the amount of energy needed to remove an electron from the ground state atom.

13. Wave Particle Duality

    • Wave particle duality theory states that particles can act as waves
    • The de Broglie equation relates a wave property (wavelength) to a moving particle property.
      • de Brouglie wavelength = Plank's constant over momentum
    • Electron Diffraction
      • Electron diffraction occurs when electrons pass through gaps in crystal graphite
      • Diffraction will only occur if the size of the particle going through the gap is (almost) the same as the gap it is trying to go through