**Electricity**

designed by Dr T. Marlow

## Specification:50 describe electric current as the rate of flow of charged particles and use the expression
I = ΔQ /Δt51 use the expression V = W/Q52 recognise, investigate and use the relationships between current, voltage and resistance, for series and parallel circuits, and know that these relationships are consequence of the conservation of charge and energy Measure current and voltage in series and parallel circuits Use ohmmeter to measure total resistance of series/parallel circuits 53 investigate and use the expressions P = VI, W = VIt. Recognise and use related expressions eg P = I^2R and P = V^2/RMeasure the efficiency of an electric motor 54 use the fact that resistance is defined by R = V/I and that Ohm’s law is a special case when I α V55 demonstrate an understanding of how ICT may be used to obtain current-potential difference graphs, including non-ohmic materials and compare this with traditional techniques in terms of reliability and validity of data 56 interpret current-potential difference graphs, including non-ohmic materials Investigate I-V graphs for filament lamp, diode and thermistor57 investigate and use the relationship R = ρl/A Measure resisitivity of a metal and polythene58 investigate and explain how the potential along a uniform current-carrying wire varies with the distance along it and how this variation can be made use of in a potential divider Use a digital voltmeter to investigate ‘output’ of a potential divider 59 define and use the concepts of emf and internal resistance and distinguish between emf and terminal potential difference Measure the emf and internal resistance of a cell eg a solar cell 60 investigate and recall that the resistance of metallic conductors increases with increasing temperature and that the resistance of negative temperature coefficient thermistors decreases with increasing temperature Use of ohmmeter and temperature sensor 61 use I = nqvA to explain the large range of resistivities of different materials. Demonstration of slow speed of ion movement during current flow62 explain, qualitatively, how changes of resistance with temperature may be modelled in terms of lattice vibrations and number of conduction electrons |