Batteries in series vs. parallel?

[mr chievous]

I know what to do with resistors and capacitors, but what about batteries in series vs. parallel? I found this online -

Series - add for total voltage, but current stays the same
Parallel - total voltage is the same but current adds

Can someone explain the above?

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[dsoz]

Let's say a typical D cell battery has 1.5v and 0.2A.

In series (positive of one touches the negative of the other) the combination has 3.0v and 0.2A. Both cells provide voltage. There is more chemical reactions occurring in two cells that can "push" the electrons more, so you get more potential.

In parallel (two batteries are next to each other, both positives are facing the same way) the combination gives 1.5v but 0.4A. The increased chemical reaction creates more electron flow at the same potential.

Sometimes it is easier to remember how it works than it is to figure out why it works. There was a point in time when I made it make sense to me and I could explain it better, but that was many years ago... sorry.

HTH
dsoz

 

[mr chievous]

Let's say a typical D cell battery has 1.5v and 0.2A.

In series (positive of one touches the negative of the other) the combination has 3.0v and 0.2A. Both cells provide voltage. There is more chemical reactions occurring in two cells that can "push" the electrons more, so you get more potential.

In parallel (two batteries are next to each other, both positives are facing the same way) the combination gives 1.5v but 0.4A. The increased chemical reaction creates more electron flow at the same potential.

Sometimes it is easier to remember how it works than it is to figure out why it works. There was a point in time when I made it make sense to me and I could explain it better, but that was many years ago... sorry.

HTH
dsoz

Thanks for the response! I understand the battery part now, but why does the current add in parallel, and not in series?

 

[NuttyEngDude]

Thanks for the response! I understand the battery part now, but why does the current add in parallel, and not in series?

kirchoffs rules, all current entering an intersection will sum to what's leaving (i paraphrased)

 

[asf503]

Thanks for the response! I understand the battery part now, but why does the current add in parallel, and not in series?

The way I see it is this: A battery can only spit out a finite amount of electrons per second, since the chemical reaction within the battery can only proceed at a maximum rate. Since batteries in series stil only have one end to spit out the electrons (i.e. only one end is still attached to the wiring), the current will stay the same in magnitude but the potential difference between the ends will be greater. I guess if this were gravity, a ball would drop from a higher point up but the man throwing the balls can only throw one ball per second, regardless of how high he is.

Contrast that with batteries in parallel, where multiple batteries can spit out their electrons into the wiring. Instead of putting out only one electron per second, two batteries each can put out one electron per second, so effectively for the circuit two electrons per second. In gravity terms, now the man and his son are both throwing balls off of a cliff.

Does that help? Or does that just confuse you?

 

[mr chievous]

Aw man, just when I thought I understood it, I read this from TBR Physics.

"Voltages add in series, so adding a battery in series will increase the total voltage of the circuit; given that resistance does not chance, according to V = IR, the total current must increase."

So were we all wrong???

 

[asf503]

aw man, just when i thought i understood it, i read this from tbr physics.

"voltages add in series, so adding a battery in series will increase the total voltage of the circuit; given that resistance does not chance, according to v = ir, the total current must increase."

so were we all wrong???

how is it possible that i am now confused?

 

[DrDashInd]

This explains it very well: http://www.science.org.au/primaryco...source/data/Phy/sub/seriespara/seriespara.htm

 

[JLeBling]

Aw man, just when I thought I understood it, I read this from TBR Physics.

"Voltages add in series, so adding a battery in series will increase the total voltage of the circuit; given that resistance does not chance, according to V = IR, the total current must increase."

So were we all wrong???

I remember reading somewhere... I wish I could remember.

Doesn't total apparent resistance rise proportionally with increased apparent voltage? Because the voltage starts off at its maximum value at the anode, and decreases down to zero before it completes the circuit and arrives at the cathode?

Ok, I got to write this one out.

 

[JLeBling]

Otherwise you get a short circuit right?

I can't find my notes where I wrote this... Someone needs to fill in.. lol

Whatever the percentage is of an INDIVIDUAL resistor to the TOTAL resistance, the voltage drop across it (the individual resistor) is the same percentage of the applied voltage.

 

[asf503]

Aw man, just when I thought I understood it, I read this from TBR Physics.

"Voltages add in series, so adding a battery in series will increase the total voltage of the circuit; given that resistance does not chance, according to V = IR, the total current must increase."

So were we all wrong???

I think I've got it!

Adding batteries will always add to the overall resistance in a circuit- this is due to the internal resistance of the battery itself. To the original single resistor that was in the circuit- say it was a lightbulb or something- the apparent current through it is higher because we are neglecting to add the increased resistance from the batteries in series and their internal resistances in series. These internal resistances would add to the total circuit, making the total resistance for the circuit higher, but for the circuit as a whole the current does not increase.

What do you guys think?

 

[MedGrl@2022]

I know what to do with resistors and capacitors, but what about batteries in series vs. parallel? I found this online -

Series - add for total voltage, but current stays the same
Parallel - total voltage is the same but current adds

Can someone explain the above?

Are we expected to know this for the MCAT? None of my study books covered it but I know there are more to circuits than capacitors and resistors in series and in parallel. Also this is what the AAMC says:

ELECTRONIC CIRCUIT ELEMENTS
A. Circuit Elements
1. Current (I = ΔQ/Δt, sign conventions, units)
2. Battery, electromotive force, voltage
3. Terminal potential, internal resistance of battery
4. Resistance
a. Ohm’s law (I = V/R)
b. resistors in series
c. resistors in parallel
d. resistivity (ρ = RA/L)
5. Capacitance
a. concept of parallel-plate capacitor
b. energy of charged capacitor
c. capacitors in series
d. capacitors in parallel
e. dielectrics
6. Discharge of a capacitor through a resistor
7. Conductivity theory
B. Circuits
1. Power in circuits (P = VI, P = I
2
R)
C. Alternating Currents and Reactive Circuits
1. Root-mean-square current
2. Root-mean-square voltage

Thus, I wasn't planning on studying it but if this is from a practice AAMC exam or you know that this could potentially show up on the MCAT. I suppose that I should study it.

 

[brood910]

EDIT: NVM. I found out that the original post is completely wrong about the current.