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Series vs Parallel Circuits

we'll be looking at some key differences

between a circuit in series and a

circuit in parallel let's start with an

example of a circuit in series in this

example we have a battery that's

connected to three light bulbs each

light bulb in the circuit is connected

end to end if we imagine a single charge

passing through this circuit we can see

that it would pass through every single

part or light bulb in this circuit this

is a characteristic of series circuits

now if we compare this to a circuit of

all of the same components but connected

in parallel we can see a key difference

let's imagine that same single charge

passing through this parallel circuit

that single charge will only pass

through one branch or one of our bulbs

in our parallel circuit each time it

passes through the circuit in our

example parallel circuit each bulb has

its own branch or connection to the

voltage source or battery whereas in the

series circuit all of our bulbs were

connected together and had the same

connection to our battery it's also

important to note then how each of these

components are connected to each other

changes the overall or total resistance

in our circuit if we were to run an

experiment on our series circuit and

added more and more light bulbs to that

circuit we would see a change in the

brightness of our bulbs the more bulbs

we add to that series circuit the dimmer

they all become this highlights the fact

that as we add more bulbs to our circuit

we're increasing the total resistance of

that circuit

this causes the total current in our

circuit to decrease this can be stated

another way as the resistance increases

in a series circuit the overall current

decreases we can see this relationship

in Ohm's law which states that the

voltage is equal to the current times

the resistance or V equals I times R

we isolate the eye or the current in

this equation we can see that as we

increase the resistance in a circuit we

decrease the current in order to

determine the total resistance of a

series circuit we simply add all of the

resistance values to each other or

example in our circuit in two of the

bulbs have a resistance of 8 ohms and

one has a resistance of 2 ohms we would

simply add 8 ohms plus 8 ohms plus 2 ohm

this gives us a total resistance of 18

ohms for our series circuit another key

thing to note about a series circuit is

if we remove any one of the bulbs the

entire circuit goes dead the electrical

current can no longer flow in one of the

components is missing if all of the

appliances in your kitchen your

refrigerator your oven your microwave

and even the lights were attached in

series then if any one of them were

turned off none of them would work so in

the case of having a series circuit in

your kitchen to run your refrigerator

you would have to have the lights up and

you would have to have the oven on and

you would have to have the microwave off

so clearly a series circuit is not what

we have in our homes let's now look at

the resistance in a parallel circuit

again if we follow that single charge as

it moves around our example parallel

circuit we can see that it has multiple

paths or multiple ways it can move

around the circuit and each single

charge will only pass through one bulb

on its way around the path parallel

circuits have an unexpected feature that

as we add more and more resistors in

parallel we actually increase the

overall current in that circuit because

of Ohm's law the same is also true that

as we add more and more resistors we're

actually decreasing the total resistance

for that circuit let's take a look at

how we calculate total resistance in a

parallel circuit

to calculate the total resistance in a

parallel circuit we add a reciprocal of

the resistance of each resistor and then

we take the reciprocal of that total

this can be shown in the following

equation so let's calculate the total

resistance of our initial parallel

circuit if we assume that we have the

same resistors in our parallel circuit

as we did in our series circuit we will

add 1 over 8 ohms plus 1 over 8 ohms

plus 1 or 2 ohm and then we will take

the reciprocal of that value this gives

us a total resistance value of our

parallel circuit of 2 ohms this is a

major difference in the overall

resistance as compared to our series

circuit which had a resistance of 18 ohm

so as we can see as we add more and more

resistors to our parallel circuit we

actually decrease the total resistance

of that circuit and therefore increase

the overall current in that circuit a

final and very important feature of our

parallel circuit is that if we remove

any of our single bulbs all of the other

bulbs will continue to stay lit if we

apply this to the same analogy of our

kitchen it means that we can run any one

of those appliances by itself whether or

not the others are on or off clearly

parallel circuits are what we have in

our home

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