[PHY] Chapter 18 - D.C Circuits

DARRELL ER (COPYRIGHTED) © TOPIC 18: D.C CIRCUITS DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

CIRCUIT DIAGRAM SERIES CIRCUIT PARALLEL CIRCUIT KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

CIRCUIT DIAGRAMS DARRELL ER (COPYRIGHTED) ©

Series Parallel Current Current is the same throughout circuit. I1 = I2 = I3 Total current is sum of current in each separate branch. Itotal = I1 + I2 + I3 Potential Difference Total P .D is sum of P .D across each component. Vtotal = V1 + V2 Potential difference is the same across each branch. Vtotal = V1 = V2 = V3 SUMMARY TABLE DARRELL ER (COPYRIGHTED) © I1 I2 I3 Itotal V3 V2 V1 Vtotal V1 V2 Vtotal A1 A2 A3

Series Parallel Resistance Total effective resistance is sum of individual resistance. Rtotal = R1 + R2 + R3 Total effective resistance is sum of reciprocal of resistance in each branch. 1 / Rtotal = 1/R1 + 1/R2 + 1/R3 SUMMARY TABLE DARRELL ER (COPYRIGHTED) © R1 R2 R3 R2 R1 R3

A RIVER VISUALISATION How electricity works in a circuit is similar to a river. Current flows in a river and at times, it can split into smaller streams. When it does, the volume of water is reduced in each smaller stream. A parallel circuit works in the same way! Current will split into smaller volume as it enters each individual branch of the circuit. Itotal = I1 + I2 + I3 smaller stream, I2 BIG STREAM current direction current direction BIG STREAM DARRELL ER (COPYRIGHTED) © I1 I2 I3 Itotal

SERIES CIRCUIT Current is the same throughout circuit. I1 = I2 = I3 (There is only 1 big stream for the river) Total potential difference is sum of P .D across each component, as the current has to pass through all the resistors. Vtotal = V1 + V2 Total effective resistance is sum of individual resistance, as current has to pass through all the resistors. Rtotal = R1 + R2 + R3 SERIES CIRCUIT A disadvantage is that when one light bulb were to fuse, the entire circuit will no longer work. DARRELL ER (COPYRIGHTED) © V1 V2 Vtotal R1 R2 R3

PARALLEL CIRCUIT Total current is sum of current in each separate branch. Itotal = I1 + I2 + I3 (River splits into smaller streams, current will get divided as well) Potential difference is the same across each branch. V = V1 = V2 = V3 Total effective resistance is sum of reciprocal of resistance in each branch. 1 / Rtotal = 1/R1 + 1/R2 + 1/R3 PARALLEL CIRCUIT An advantage is that when one light bulb were to fuse the other parallel branches will still work. DARRELL ER (COPYRIGHTED) © I1 I2 I3 Itotal V3 V2 V1 Vtotal

AN IMPORTANT CONCEPT VISUALISATION smaller stream, I2 BIG STREAM current direction current direction BIG STREAM So let’s visualise this. This group of pikachu are the charges flowing in the river (current). They have 3 options, which path do you reckon they will take? Like most lazy humans, its will be the path of least resistance! Most pikachus will go down stream I3. Some will go to stream I2. Only a few will go to stream I1. As current is the rate of flow of charges and charges tend to take the path of least resistance, Current will split differently into each stream based on the amount of resistance in that branch. I1 = I2 = I3 only when the reistance in each branch happens to be the same! No hate on caterpie though! DARRELL ER (COPYRIGHTED) © I1 I2 I3 Itotal