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D.C. Circuits - Objectives
• Practical circuits
• Electromotive force and internal resistance
• Kirchhoff’s laws
• Series and parallel arrangements
• Potential divider
• Electrical energy and power
Candidates should be able to:
- recall and use appropriate circuit symbols as set out in SI Units, Signs, Symbols and Abbreviations (ASE, 1981) and Symbols and Systematics (ASE, 1995).
- draw and interpret appropriate circuit diagrams.
- use the concept that e.m.f. is defined in terms of the energy transferred by a source in driving unit charge round a complete circuit.
- use energy considerations to distinguish between e.m.f. and p.d.
- know Energy E = I V t, P = IV, P = I2R, P=V2/R
- application, e.g. Understanding of high current requirement for a starter motor in a motor car.
- appreciate that sources of e.m.f. have internal resistance and understand the simple consequences of internal resistance for external circuits.
- recall and use ε = E/Q and ε = I (R + r)
- differentiate between emf and terminal pd
- understand and perform calculations for circuits in which the internal resistance of the supply is not negligible
- Applications; e.g. low internal resistance for a car battery.
- Conservation of charge and energy in simple dc circuits.
- recall Kirchhoff’s first law and appreciate this as a consequence of conservation of charge.
- understand Kirchhoff’s second law as a consequence of conservation of energy.
- The relationships between currents, voltages and resistances in series and parallel circuits, including cells in series and identical cells in parallel.
- recall and use a formula for the combined resistance of two or more resistors in series: RT = R1 + R2 + R3 + …
- recall and use a formula for the combined resistance of two or more resistors in parallel: 1/RT = 1/R1 + 1/R2 + 1/R3 + …
- understand the use of a potential divider as a source of constant or variable p.d.; e.g. application as an audio volume control
- describe and explain the use of variable resistors, thermistors and light-dependent resistors in potential dividers to provide a potential difference which is dependent on temperature and on light intensity respectively.
- convert between different units of the same quantity, e.g. J and eV, J and kWh
- REQUIRED PRACTICAL - investigation of the emf and internal resistance of electric cells and batteries by measuring the variation of the terminal pd of the cell with the current in it
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