# Physics Unit 1

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• Physics Unit 1
• Atomic  structure
• Atom has a positively charged nucleus surrounded by negatively charged electrons
• Protons and neutrons are called nucleons
• Isotopes are atoms with the same number of protons and diffident number of neutrons
• A =  Mass or nucleon number
• Z =  Atomic or proton number
• Uncharged atoms have equals numbers of protons no electrons
• A nuclide is a type of nucleus with a particular number of protons and neutrons
• Specific charge = charge ÷ (nucleon x electron mass)
• The election has the highest specific charge out of all the other particles
• The higher the neutron : proton ratio the more unstable the nucleus is
• The strong nuclear force is an attractive force between nucleons that holds them in the nucleus
• A range of no more than 3-4 fm
• Same effect between al nucleons
• Below a separation of 0.5 fm it is a repulsive force
• To prevent nucleons from being pushed into each other
• Alpha radiation consists of alpha particles (2 protons, 2 neutrons)
• Beta radiation consists of fast moving electrons
• Carries away excess energy
• Beta minus decay produces an antineutrino
• Beta plus decay produces a neutrino
• Wavelength of electromagnetic radiation ? = c ÷ f
• Electric wave and magnetic wave travel together and vibrate perpendicularly and in phase
• A charged particle emits EM waves when it loses energy
• Eg.  When a fast moving electron slows down or changes direction or when an electron moves to a lower energy level in an atom
• Emitted burst of EM waves are called photons
• A photon has an energy if E = hf
• The power of a beam of photon = nhf  where n is the number of photons passing a point per second
• antiparticles annihilate their     corresponding particles when they meet
• They have the same rest mass as the particle and opposite charge
• Annihilation produces two photons (mass is converted to energy)
• Min energy of each photon = hf = E?
• For pair production a photon needs an energy hf = 2E?