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Physics AS - Electricity
Transcript of Physics AS - Electricity
there are many free electrons in the metals
electrons move through the metal - collide with vibrations of the lattice and are scattered
metal get hotter - atoms vibrate more
therefore more collisions between atoms and electrons
so, current decreases, resistance increases Semiconductors - contain fewer free electrons than metals semiconductors with a NTC have resistance that decreases with temperature because... as the material gets hotter, increased vibration of the atoms releas more electrons - this increases current which decreases resistance semiconductors with a PTC have resistance that increases with temperature Power & Work Power is the rate of doing work or the rate of transfer of energy. Resistance & Resistivity Resistors in Series Current - same
Voltage - adds up so, Resistors in parallel Current - adds up
Voltage - same so, Where is resistivity the units for resistivity are is a measure of how strongly a material opposes the flow of electric current Resistivity Number
conduction electrons Number density - the number of charge carriers that can move per Potential Dividers A potential divider consists of two (or more) resisters connected in series. Because they are in series, the same current flows through both resisters, and the p.d is divided between them Internal Resistance The emf of a power supply is the total energy it supplies to each coulomb of charge.
Many power supplies have some internal resistance, so some of the energy supplies to each coulomb is 'lost' due to heating with in the power supply the formula for finding the internal resistance is: