Physics OCR A Level Nuclear and Particles Physics: Module 6: Particles and Medical Physics: Questions with Complete Solutions

How does the alpha-scattering experiment give evidence of a small, dense nucleus? A few alpha particles bounce back. This wouldn’t happen if the positive charge in the atom was distributed evenly throughout (as in the Plum Pudding Model), which suggests they must be hitting a dense positive charge. The fact it only happens to a very small number of alpha particles shows the nucleus must be small. What are the main constituents of an atom? ● Proton ● Neutron ● Electron How many times bigger is an atom than a nucleus? Approximately 100,000 times. What is the letter associated with a proton number? Z What is a nucleon? A particle that makes up the nucleus: a protons or a neutron. What letter represents nucleon number? A What is the definition of an isotope? Isotopes are atoms of an element (with the same number of protons) with a different number of neutrons (and therefore a different mass number). What is the strong nuclear force? The force that holds the nucleus together. It must overcome the electrostatic force of repulsion between protons, but not so much as to cause the nucleus to collapse. Describe the range of the strong force. Repulsive up to 0.5fm. Attractive up to 3fm. What is the equation relating radius of an atom and its nucleon number? r = r₀A¹/³ where: r = radius, r₀ = constant (for all atoms), A = nucleon number Which has a higher density: an atom or a nucleus? A nucleus is much more dense than an atom because the atom includes a lot of empty space. Ture or false ‘Every particle has a antiparticle.’