Greenridge Sec Physics 2024 Chap 18 Notes

Secondary Four (Express) Chapter 18 – DC Circuits Physics Notes - 1 - Prepared by: Mr Yong W. S. Greenridge Secondary School Secondary Four Express Physics Chapter 18 – D.C. Circuits (Notes Part 1) Name: ( ) Class: 4-8 Date: 5 April 2024 At the end of this chapter, you should be able to ☺ Draw circuit diagrams with power source (cell or battery), switches, lamps, resistors (fixed and variable), fuses, ammeters and voltmeters, bells, light-dependent resistors, thermistors and light-emitting diodes (LED). ☺ State that the current at every point in a series circuits is the same and apply to new situations or to solve related problems. ☺ State that the sum of the potential differences in a series circuits is equal to the potential difference across the whole circuit and apply to new situations or to solve related problems. ☺ State that the current from the source is the sum of the currents in the separate branches of a parallel circuit and apply to new situations or to solve related problems. ☺ State that the potential difference in a parallel circuit to new situations or to solve related problems. ☺ Recall and apply the relevant relationship, including R = V/I and those for potential differences in series and in parallel circuits, resistors in series and in parallel, in calculations involving a whole circuit. ☺ describe the action of a variable potential divider (potentiometer) ☺ describe the action of thermistors and light-dependent resistors and explain their use as input transducers in potential dividers ☺ solve simple circuit problems involving thermistors and light-dependent resistors Additional Circuit Symbol Thermistor Light-Dependent Resistor Light-Emitting Diode (LED)

Secondary Four (Express) Chapter 18 – DC Circuits Physics Notes - 2 - Prepared by: Mr Yong W. S. SERIES Parallel Diagram Potential Difference Current Resistance

Secondary Four (Express) Chapter 18 – DC Circuits Physics Notes - 3 - Prepared by: Mr Yong W. S. Example 1 The circuit shown consists of a 12 V cell of negligible resistance. The ammeter measures a current of 0.5 A. Find (a) the p.d. across the 15  resistor (b) the p.d. across the resistor R (c) the value of resistor R Description Hybrid Diagram Current Potential Difference Resistance A 15  R 12 V

Secondary Four (Express) Chapter 18 – DC Circuits Physics Notes - 4 - Prepared by: Mr Yong W. S. Example 2 The circuit shown consists of 2 resistors of 4  and 2  connected in series. (a) What is the ammeter reading? (b) What is the potential difference across the 2  resistor? A 2  4  4 V

Secondary Four (Express) Chapter 18 – DC Circuits Physics Notes - 5 - Prepared by: Mr Yong W. S. Example 3 The circuit shown consists of a 6 V cell of negligible resistance. The circuit also consists of 2 resistors of 4  and 2  connected in parallel. Find (a) current, I1 across the 4  resistance. (b) current, I2 across the 2  resistance. (c) current, I3. Example 4 Find the magnitude of current I1, I2 and I3 in the following circuit. 4  2  6 V I1 I2 I3 I1 I2 I3 2  3  1  3 V

Secondary Four (Express) Chapter 18 – DC Circuits Physics Notes - 6 - Prepared by: Mr Yong W. S. Quiz Time Example 5 Fig. 5.1 shows a circuit containing four identical resistors, R1 to R4 and two switches S1 and S2. The rating for each resistor is ‘24 W, 12 V’. Fig. 5.1 (a) Calculate the resistance for each resistor. (b) When both switches are closed, calculate I, the current leaving the cell. Would you connect 5 light bulbs in series or parallel? State reasons for it. S2 R2 S1 12 V R1 R3 R4 I 