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AS Module 3 Current Electricity and Elastic Properties of Solids |
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| 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 charac- teristics | 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 | RT=R1 + R2 + R3
1/RT = 1/R1 + 1/R2 + 1/R3 |
| 12.1.6 Energy and power in d.c. circuits | Recall and use of E =ItV P =VI P = I2 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 hi-fi volume control |
| 12.1.9 Electro- motive 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 peak-to-peak values, for sinusoidal waveforms: |
| Irms = I0 / Ö2 Vrms = V0 / Ö2 | |
| Application to calculation of mains electricity peak and peak-to-peak voltage values | |
| 12.1.11 Oscill- oscope | 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 stress-strain curves | |
| 12.2.2 The Young modulus | The Young modulus = tensile stress / tensile strain = (F l) / (Ae) |
| One simple method of measurement Use of stress-strain graphs to find the Young modulus and strain energy per unit volume. | |