EJC Physics H215 DC Circuits - 1. Notes (2024)

Page 1 of 16 9749(2024) H2 Physics H215 D.C. Circuits – Notes H2 Topic 15 – D.C. Circuits A simple printed circuit board (PCB). A PCB is a mechanical support for the layout and electrical connection between electronic components. A PCB can have many layers sandwiched together, which allow many different connections between components within a small physical area. Content • Circuit symbols and diagrams • Series and parallel arrangements • Potential divider • Balanced potentials Learning Outcomes Candidates should be able to: (a) recall and use appropriate circuit symbols as set out in the ASE publication Signs, Symbols and Systematics (The ASE Companion to 16–19 Science, 2000) (b) draw and interpret circuit diagrams containing sources, switches, resistors, ammeters, voltmeters, and/or any other type of component referred to in the syllabus (c) solve problems using the formula for the combined resistance of two or more resistors in series (d) solve problems using the formula for the combined resistance of two or more resistors in parallel (e) solve problems involving series and parallel circuits for one source of e.m.f. (f) show an understanding of the use of a potential divider circuit as a source of variable p.d. (g) explain the use of thermistors and light-dependent resistors in potential divider circuits to provide a potential difference which is dependent on temperature and illumination respectively (h) recall and solve problems by using the principle of the potentiometer as a means of comparing potential differences 15.0 Introduction A direct current (D.C.) circuit is one where the direction of flow of current is maintained in the same direction. Such circuits are the basis for most (if not) all digital devices – the “power brick” connected to our laptops and the “mobile phone chargers ” convert household alternating current (A.C.) electricity into D.C. for use by the devices. Here, we learn how to represent real circuits using symbols and diagrams, and to apply conservation of (i) electric charge and (ii) energy when analysing circuits. A typical AC/DC adaptor. This particular “handphone charger” converts household electricity into a 5V D.C. source and supplies a maximum of 1 A to the device.

Page 2 of 16 9749(2024) H2 Physics H215 D.C. Circuits – Notes 15.1 Circuit Symbols cell switch junction of conductors battery of cells or earth galvanometer (a sensitive ammeter) or ammeter voltmeter oscilloscope power supply a.c. power supply thermistor fixed resistor variable resistor light- dependent resistor (LDR) potentiometer diode light-emitting diode (LED) lamp heater transformer 15.2.1 Resistors in Series When 2 or more resistors are connected in series, the effective resistance effR is the sum of the resistances. The electric current only has 1 possible path to flow. By conservation of charge, the