RI Chap 16 Circuits Lecture Notes

16 CIRCUITS H2 Physics 9478 Content Page 16.1 Circuit symbols and diagrams 2 16.2 Resistance, resistivity, and internal resistance 4 16.3 Resistors in series and in parallel 16 16.4 RC circuits with d.c. source 42 16.5 Appendix 49 Learning Outcomes Candidates should be able to: (a) recall and use appropriate circuit symbols. (b) draw and interpret circuit diagrams containing sources, switches, resistors (fixed and variable), ammeters, voltmeters, lamps, thermistors, light-dependent resistors, diodes, capacitors and any other type of component referred to in the syllabus. (c) define the resistance of a circuit component as the ratio of the potential difference across the component to the current in it, and solve problems using the equation V = IR. (d) recall and solve problems using the equation relating resistance to resistivity, length and cross-sectional area, lρ=R A . (e) sketch and interpret the I-V characteristics of various electrical components in a d.c. circuit, such as an ohmic resistor, a semiconductor diode, a filament lamp and a negative temperature coefficient (NTC) thermistor. (f) explain the temperature dependence of the resistivity of typical metals (e.g. in a filament lamp) and semiconductors (e.g. in an NTC thermistor) in terms of the drift velocity and number density of charge carriers respectively. (g) show an understanding of the effects of the internal resistance of a constant source of e.m.f. on the terminal potential difference and output power. (h) solve problems using the formula for the combined resistance of two or more resistors in series. (i) solve problems using the formula for the combined resistance of two or more resistors in parallel. (j) solve problems involving series and parallel arrangements of resistors for a constant source of e.m.f., including potential divider circuits which may involve NTC thermistors and light-dependent resistors. (k) solve problems using the formulae for the combined capacitance of two or more capacitors in series and in parallel. (l) describe and represent the variation with time, of quantities like current, charge and potential difference, for a capacitor that is charging or discharging through a resistor, using equations of the form ( )τ= −0 exp /xx t or ( )[ ]τ=−−0 1 exp /xx t , where τ = RC is the time constant.

Page | 2 16.1 Circuit symbols and diagrams  Circuit Symbols The following is a list of circuit symbols used in the syllabus. Category Component Circuit Symbol Function of Component Wires and Connections Wire To pass current from one part of a circuit to another. Wires that are connected This symbol is used in circuit diagrams where wires cross to show that they are connected (joined). Wires that are not connected In complex circuit diagrams it is often necessary t