# D.C. Circuits - Objectives

Content

• Practical circuits
• Electromotive force and internal resistance
• Kirchhoff’s laws
• Series and parallel arrangements
• Potential divider
• Electrical energy and power

Learning Outcomes

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.
• 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 