AS Module 3 Current Electricity and Elastic Properties of Solids 

Introduction This module contains principally simple current electricity including alternating currents and the use of the oscilloscope. Some work on elastic properties of solids is also included. Most of this module consists of material from the AS Criteria for Physics. You MUST learn the formula in bold  
12.1 Current electricity  
12.1.1 Charge, current, potential difference  Electrical current as the rate of flow of charge 
Recall and use of I=DQ/Dt V = W/Q  
Resistance  Resistance is defined by R = V / I 
12.1.2 Current/voltage characteristics  For an ohmic conductor, a semiconductor diode and a filament lamp Candidates should have experience of the use of a current sensor and a voltage sensor with a datalogger to capture data from which to determine V – I curves 
12.1.3 Ohm's law  Ohm’s law understood as a special case where I a V 
12.1.4 Resistivity  Recall and use of r = AR/l 
Description of the qualitative effect of temperature on the resistance of metal conductors and thermistors. Applications, e.g. temperature sensors  
12.1.5 Series and parallel resistor circuits  R_{T}=R_{1} + R_{2} + R_{3}
1/R_{T} = 1/R_{1} + 1/R_{2} + 1/R_{3} 
12.1.6 Energy and power in d.c. circuits  Recall and use of E =ItV P =VI P = I^{2} R 
Application, e.g. understanding of high current requirement for a starter motor in a motor car  
12.1.7 Kirchhoff’s laws  Conservation of charge and energy in simple d.c. circuits The relationships between currents, voltages and resistances in series and parallel circuits; questions will not be set which require the use of simultaneous equations to calculate currents or potential difference 
12.1.8 Potential divider  The potential divider used to supply variable p.d. e.g. application as a hifi volume control 
12.1.9 Electromotive force Î Internal resistance r  Î = E/Q Î = I(R + r) 
12.1.10 Alternating currents  Sinusoidal voltages and currents only; root mean square, peak and peaktopeak values, for sinusoidal waveforms: 
I_{rms} = I_{0} / Ö2 V_{rms} = V_{0} / Ö2  
Application to calculation of mains electricity peak and peaktopeak voltage values  
12.1.11 Oscilloscope  Use of an oscilloscope as a d.c. and a.c. voltmeter, to measure time intervals and frequencies, and to display waveforms 
12.2 Elastic properties of solids  
12.2.1 Bulk properties of solids  Density r. Recall and use of r = m / V 
Hooke’s law, elastic limit, experimental investigations Tensile strain and tensile stress Elastic strain energy, breaking stress Derivation of energy stored = 1/2 Fe Description of plastic behaviour, fracture and brittleness and interpretation of simple stressstrain curves  
12.2.2 The Young modulus  The Young modulus = tensile stress / tensile strain = (F l) / (Ae) 
One simple method of measurement Use of stressstrain graphs to find the Young modulus and strain energy per unit volume.  