Physics Unit 2

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Unit 2.1 Resultant forces - Two objects interact --> forces exerted are equal and opposite... Forces at a point --> replaced by single force that has the same effect on the motion as the original forces all acting together (resultant force)... RF may change motion

Unit 2.3 Resistance - Pd / Current... Greater the R, smaller the current for a Pd

Circuits - Series --> Same current through each component, total pd is shared between components... Parallel --> Pd across each component same, total current is sum of the currents through the separate components

Unit 2.4 Fuses - Electrical fault --> too great a current --> circuit disconnected by a fuse or circuit breaker in the live wire... Current in a fuse wire too great --> will melt, breaking the circuit

Unit 2.5

Alpha, Beta + Gamma - Alpha (stopped by human hand) --> 4, 2... Beta (stopped by sheet of aluminium) --> An electron... Gamma (stopped by lead) --> Electromagnetic radiation... Half-life --> Average time for no. of nuclei of the isotope in a sample to halve OR time it takes for count rate from a sample containing the isotope to fall to half its initial level

Background radiation - Cosmic rays --> radiation that reaches the Earth from space... Rocks + Soil --> some rocks are radioactive and give off radioactive radon gas... Plants --> Absorb radioactive materials from the soil and these pass up the foodchain

Unit 2.6

Nuclear fission - Uranium-235 + plutonium-239... Splitting of an atomic nucleus, absorb a neutron --> splits into two smaller nuclei (two or three neutrons + energy released) --> May start a chain reaction

Nuclear fusion - Joining of two atomic nuclei

Stars - Main sequence of stars life cycle is stable because the forces within it are balanced...