Edexcel IGCSE Physics Unit 1: Components in Series & Parallel Circuits PDF

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Physics (Modular): Unit 1 Components in Series & Parallel Circuits Contents Currentin Series & Parallel Voltage in Series & Parallel Resistors in Series IV Graphs Electrical Components Page 1 of 24 © 2015-2025 Save My Exams, Lt...

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Physics (Modular): Unit 1 Components in Series & Parallel Circuits Contents Currentin Series & Parallel Voltage in Series & Parallel Resistors in Series IV Graphs Electrical Components Page 1 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Current in Series & Parallel Current in series circuits There are two ways ofjoining electrical components: in series in parallel Current in series A series circuitis a circuitthat has only one loop, or one path thatthe electrons can take In a series circuit,the current has the same value at any point This is because the electrons have only one path they can take Therefore,the number of electrons passing a fixed point per unittime is the same at all locations This means that all components in a series circuit have the same current The current is the same at each point in a series circuit The amount of current flowing in a series circuit depends on: the voltage ofthe power source the number(and type) of components Increasing the voltage ofthe power source drives more current around the circuit Page 2 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources So, decreasing the voltage ofthe power source reduces the current Increasing the number of components in the circuitincreases the totalresistance Hence less current flows through the circuit Increasing the voltage and number of components in series Current will increase if the voltage of the power supply increases and decreases if the number of components increases Current in parallel circuits A parallel circuitis a circuitthat has two or more loops, or more than one path that electrons can take Parallel circuits contain junctions and branches Junctions are points where two or more wires meetto form a new branch Branches are the sections of wire between junctions Current in parallel In a parallel circuit,the current has different values at different points in the circuit Page 3 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources This is because the current splits at a junction Therefore,the electrons have different paths they can take The sum ofthe currentin the individual branches is equalto the total current before (and after)the branches Current splits at a junction into individual branches Why is current conserved at a junction in a circuit? At a junction,the currentis always conserved This means the amount of current flowing into the junction is equalto the amount of current flowing out ofit This is because the charge is conserved Current does not always split equally – often there will be more currentin some branches than in others The currentin each branch will only be identical ifthe resistance ofthe components along each branch is identical Current behaves in this way because itis the flow of electrons: Electrons, or any charge, cannot be created or destroyed Page 4 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources This means the total number of electrons (and hence current) going around a circuit mustremain the same When the electrons reach a junction, however, some ofthem will go one way and the rest will go the other Worked Example In the circuit below, ammeter A shows a reading of10 A, and ammeter A shows a reading of 6 A. 0 1 Whatis the reading on ammeter A ? 2 Answer: Step 1: Recall what happens to the current at a junction At a junction,the current splits, butis always conserved This means thatthe total amount of current flowing into a junction is equalto the total amount flowing out Step 2: Consider the first junction in the circuit where the current splits The diagram below shows the firstjunction in the circuit Page 5 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Step 3: Calculate the missing amount of current Since 10 A flows into the junction (the total currentfrom the battery),10 A must flow out ofthe junction The question says that 6 A flows through ammeter A so the remaining current flowing through 1 ammeter A must be: 2 10 A − 6 A = 4 A Therefore, 4 A flows through ammeter A 2 Examiner Tips and Tricks The direction of current flow is super important when considering junctions in a circuit. You should rememberthat current flows from the positive terminalto the negative terminal of a cell / battery. This will help determine the direction currentis flowing 'in'to a junction and which way the currentthen flows 'out'. Page 6 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Voltage in Series & Parallel Voltage in series & parallel Voltage in series In a series circuit,the total voltage of a power supply is shared between the components Lamps connected in a series circuit share the potential difference from the battery Fortwo identical components (with equal resistance),the voltage across them will be: the same equalto half the total voltage ofthe power supply Fortwo non-identical components (with different values ofresistance),the voltage will be: higher across the component with the higher resistance lower across the component with lower resistance Voltage in parallel In a parallel circuit,the total voltage across each branch is the same as the voltage ofthe power supply Page 7 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Lamps connected in a parallel circuit all have the same voltage across them Advantages & disadvantages Advantages and disadvantages of a series circuit A series circuit consists of a string oftwo or more components connected in a loop Page 8 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources In a series circuit, only one switch is needed to control all of the lamps. This can be seen as an advantage or as a disadvantage Advantages of a series circuit All ofthe components are controlled by a single switch Fewer wires are required Disadvantages of a series circuit The components cannot be controlled separately If one component breaks, all other components stop working Advantages and disadvantages of parallel circuits A parallel circuit consists oftwo or more components attached across different branches ofthe circuit In a parallel circuit, the lamps are connected in parallel and can be switched on and off by their own switches Advantages of a parallel circuit The components can be individually controlled using their own switches Page 9 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources If one component breaks,then the others will continue to function Disadvantages of a parallel circuit Many more wires are involved which can be more complicated to set up All branches have the same voltage as the supply making it more difficultto controlthe voltage across individual components Examiner Tips and Tricks You may have noticed thatfor a parallel circuit, all ofthe components can be controlled by a single switch - like a series circuit. Nevertheless,the exam board still considers this an advantage of series circuits. Note thatthe current does not always split equally in a parallel circuit – often there will be more currentin some branches than in others. The currentin each branch will only be identical ifthe resistance ofthe components along each branch are identical. However,the voltage across two components connected in parallel is always the same  Page 10 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Resistors in series Head to www.savemyexams.com for more Resistors in Series awesome resources Your notes When two or more resistors are connected in series,the totalresistance is equalto the sum oftheir individual resistances Fortwo resistors ofresistance R and R ,the total resistance can be calculated using the equation: 1 2 R = R1+ R2 Where: R is the total resistance, in ohms (Ω) Increasing the number ofresistors increases the overall resistance The charge now has more resistors to pass through The total voltage is also the sum ofthe voltages across each ofthe individualresistors Three resistors connected in series. The total voltage is the sum of the individual voltages, and the total resistance is the sum of the three individualresistances Page 11 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Summary of series and parallel circuits For components connected in series: the current is the same at all points and in each component the voltage ofthe power supply is shared between the components the totalresistance is the sum ofthe resistances of each component For components connected in parallel: the current from the supply splits in the branches the voltage across each branch is the same the totalresistance is less than that of each component Worked Example The combined resistance R in the following series circuitis 60 Ω. Whatis the resistance value of R ? 2 A 100 Ω B 30 Ω C 20 Ω D 40 Ω ANSWER: C Step 1: Write down the equation for the combined resistance in series R = R1+ R2+ R3 Step 2: Substitute the values for totalresistance R and the otherresistors 60 Ω = 30 Ω + R + 10 Ω 2 Page 12 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Your notes Head to www.savemyexams.com for more awesome resources Step 3: Rearrange for R 2 Your notes R = 60 Ω – 30 Ω – 10 Ω = 20 Ω 2 Worked Example Dennis sets up a series circuit as shown below. The cell supplies a current of 2 A to the circuit, and the fixed resistor has a resistance of 4 Ω. (a) How much current flows through the fixed resistor? (b) Whatis the reading on the voltmeter? Answer: Part(a) Step 1: Recall that current is conserved in a series circuit Since currentis conserved in a series circuit, itis the same size if measured anywhere in the series loop This means that since the cell supplies 2 A to the circuit,the currentis 2 A everywhere Therefore, 2 A flows through the fixed resistor Part(b) Step 1: List the known quantities Current, I = 2 A Resistance, R = 4 Ω Step 2: State the equation linking potential difference,resistance and current Page 13 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources The equation linking potential difference, resistance and currentis: V=I×R Step 3: Substitute the known values into the equation and calculate the potential difference V = 2 × 4 = 8 V Therefore,the voltmeter reads 8 Vacross the fixed resistor Page 14 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Your notes Head to www.savemyexams.com for more awesome resources IV Graphs IV graphs Your notes When the voltage V across a componentis varied,the currentI flowing through it may vary linearly or non-linearly The relationship between current and voltage of a component can be shown on an IV graph When the relationship between current and voltage is linear: the IV graph is a straight line which passes through the origin the resistance is constant When the relationship between current and voltage is non-linear: the IV graph thatis not a straightline the resistance is not constant Linear and non-linearIV graphs LinearIV graphs are straight lines through the origin,indicating a constant resistance. Non-linearIV graphs are curved,indicating a variable resistance Components with linearIV graphs include: Page 15 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources fixed resistors (at constanttemperature) wires (at constanttemperature) Components with non-linearIV graphs include: filamentlamps diodes LDRs thermistors IV graph for a wire or a resistor The relationship between current and voltage for a wire or fixed resistor is linear, or directly proportional, which means the IV graph is a straightline, so voltage and currentincrease (or decrease) by the same amount the slope ofthe graph is constant, so resistance is constant The current is directly proportional to the potential difference (voltage) as the graph is a straight line through the origin IV graph for a filament bulb Page 16 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources The relationship between current and voltage for a filamentlamp is non-linear, or not directly proportional, which means the IV graph is not a straightline, so voltage and current do not increase (or decrease) by the same amount the slope ofthe graph is not constant, so resistance changes The IV graph for a filamentlamp shows as voltage increases the currentincreases at a proportionally slowerrate the resistance increases;the flatterthe slope,the higherthe resistance IV graph for a filament lamp As currentthrough a filamentlamp increases,the resistance increases because: the higher current causes the temperature ofthe filamentto increase the highertemperature causes the atoms in the metal lattice ofthe filamentto vibrate more this causes an increase in resistance as it becomes more difficultfor free electrons (the current)to pass through since resistance opposes the current,this causes itto increase at a slowerrate IV graph for a diode Page 17 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources A diode allows currentto flow in one direction only This is called forward bias In the reverse direction,the diode has very high resistance, and therefore no current flows This is called reverse bias When the currentis in the direction ofthe arrowhead symbol,this is forward bias On the IV graph,this is shown by a sharp increase in voltage and current on the right side ofthe graph This shows the resistance is very low When the diode is switched around,this is reverse bias On the IV graph,this is shown by a zero reading of current or voltage on the left side ofthe graph This shows the resistance is very high IV graph for a semiconductor diode Investigating the relationship between current and voltage In orderto investigate the relationship between current and voltage different components,the following equipmentis required: an ammeter - to measure the currentthrough the component Page 18 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources a voltmeter - to measure the voltage across the component a variable resistor - to vary the currentthrough the circuit a power source - to provide a source of potential difference (voltage) wires - to connectthe components together in a circuit The image below shows the circuits set up to obtain IV graphs for a filamentlamp and a diode These circuits enable the investigation of current and voltage for a filament lamp or diode to be investigated The current is the independent variable The variable resistoris used to change the current flowing through the filamentlamp / diode The voltage is the dependent variable The voltmeteris used to measure the voltage across the filamentlamp / diode  Recording measurements of current and voltage as the currentincreases enables an IV graph to be plotted for each component Resistance Resistance is the opposition to the flow of current The higherthe resistance of a circuitthe lowerthe current Resistors come in two types: Page 19 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Fixed resistors Variable resistors Your notes Fixed resistors have a resistance thatremains constant Variable resistors can change the resistance by changing the length of wire that makes up the circuit A longerlength of wire has more resistance than a shorter length of wire Fixed and variable resistor circuit symbols  Page 20 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Thermistors & LDRs Head to www.savemyexams.com for more Electrical Components awesome resources Your notes Environmental conditions, such as temperature and lightintensity, can influence the resistance of resistors, such as Thermistors Light-dependentresistors (LDRs) Thermistors The resistance of a thermistor depends on its temperature The resistance of a thermistor is high in cold conditions and low in hot conditions As  the temperature increases the resistance of a thermistor decreases As the temperature decreases the resistance of a thermistor increases The resistance of a thermistor depends on its temperature The relationship between resistance and temperature for a thermistor can be shown on a graph Page 21 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes  The graph of resistance against temperature for a thermistor shows a curve indicating these quantities are inversely proportional to each other Light-dependent resistors (LDRs) The resistance of a light-dependent resistor(LDR) depends on the light intensity on it The resistance of an LDR is high in dark conditions and low in bright conditions As the lightintensity increases the resistance of an LDR decreases As the lightintensity decreases the resistance of an LDR increases Page 22 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources The resistance of an LDR depends on the intensity of light on it The relationship between resistance and lightintensity for an LDR can be shown on a graph Page 23 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Your notes Head to www.savemyexams.com for more awesome resources Lamps & LEDs The graph of light intensity against temperature for an LDR shows a Lamps and light-emitting diodes (LEDs) illuminate (light up) when a curve indicating these quantities are inversely proportional to each other current flows through them This makes them usefulfor indicating the presence of a currentin a circuit Light-emitting diodes (LEDs) LEDs are a type of diode This means they only allow currentto flow through them in one direction Therefore, in a circuit, an LED will only light up ifitis placed in the correct direction The circuit symbolfor an LED is as follows: LEDs can be used to indicate the presence of a current as they illuminate when current flows through them. The same is true forlamps Examiner Tips and Tricks Make sure you learn the various symbols mentioned on this page. Many ofthem are very similar with small differences denoting whatthey do: Two arrows pointing towards a symbol mean thatitis light-dependent Two arrows pointing away mean thatitis light-emitting Symbols are sometimes drawn with circles around them (e.g.the LDR). These circles are often optional (although notin the case of meters and bulbs). Page 24 of 24 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes