# What is the voltage at the negative terminal of a battery?

#### Mooney117

Joined May 27, 2020
10
Hey everyone,

I'm just starting out doing electronics as a hobby in these troubled times and I'm having trouble understanding voltage:

I have a book on electronics "Electronics for dummies" and it says:

"Voltage can be considered positive or negative , but only when compared with some reference point. For example, the voltage at the positive terminal of a flashlight battery is +1.5V relative to the negative terminal. The voltage at the negative terminal is -1.5V relative to the positive terminal."

So if I have a 9V battery does that mean positive terminal is +9v and the negative terminal is -9V making the total voltage 18V?

Or is the negative terminal 0V and the positive is +9V making the total voltage 9V?

Joined Jul 18, 2013
21,966
You have to set a reference point, which is normally considered zero.
In the case of your 9v battery, if you use the Neg terminal as the zero reference, then WRT to this zero point, the +ve terminal you will therefore read +9v.
Max.

• narkeleptk

#### ericgibbs

Joined Jan 29, 2010
11,567
hi Mooney,
Welcome to AAA,
Exchange the word relative to 'with respect to'
E

• Delta prime

#### DickCappels

Joined Aug 21, 2008
6,779
Like they said, no. It means if you take a voltmeter and measure across the two battery terminals you will measure 9 volts

The voltmeter has a polarization if you put the negative probe on the battery's negative terminal and the positive probe on the battery's positive terminal you will measure 9 volts. If you reverse the meter's probes you will measure -9V.

More than you want to know: https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter/all

#### MrChips

Joined Oct 2, 2009
22,487
So if I have a 9V battery does that mean positive terminal is +9v and the negative terminal is -9V making the total voltage 18V?

Or is the negative terminal 0V and the positive is +9V making the total voltage 9V?
A 9V battery has two terminals, one labeled + and the other labeled -.

Take a volt meter and connect the RED lead to the + terminal.
Where are you going to connect the BLACK lead of the voltmeter?

Pay attention: The + terminal is NOT at 9V.

Measuring voltage is like measuring distance.
What is the distance at London? That is a meaningless question.
What is the distance between London and Manchester? Now there is an answer to that question.

#### Audioguru again

Joined Oct 21, 2019
2,369
The example with the 1.5V battery is correct and it does NOT say it produces 3V, so why did you thing a 9V battery produces 18V??

#### Alec_t

Joined Sep 17, 2013
11,796
It may help if you note that 'voltage' is the measure of potential difference. A difference requires two measurement points, either of which can be taken as a reference point.

• narkeleptk

#### KeepItSimpleStupid

Joined Mar 4, 2014
4,370
You can place batteries in series too where they could add or subtract depending on the direction. You would have your multimeter attached to two "0-reference" points of a single battery. so, -1.5+(-9). Think of current as a loop. This will become apparent when you learn Kirkoff's Law and "Loop equations".

"Conventional current" has a negative to positive direction. Our battery has a (-) and (+) terminal, so if you enter the 1.5V battey at the (-) terminal and exit throught the +, that is +1.5V. Now you encounter a 9V battery at the +terminal. This is now -9V.
The voltage from end to end is +1.5-9, the way we defined our 0V reference.

You can place two 9V batteries together where the middle point is zero and get a +9 and -9V supply.

"conventional current" is NOT electrons. It's direction is negative to positive. Your DVM and current meters when you observe polarity will show this.

It matters in solid state physics, electro-chemistry and vacuum tubes and electron beams to some extent. The "water analogy" breaks very quickly: Voltage as pressure, Current as Flow and resistance the size of the pipe works for basic understanding.
It doesn't mean you put one electron in at one end of the wire and it comes out the other like water would.

I want to add something. Every component has parasitics. We "model" components as ideal devices. "Sometimes" three 1K resistors in series is not 3000 ohms. Sometimes a surface mount 1K resistor soldered on the thin edge is not the same component soldered on the wide edge. A wire moving on the earth is a generator, but don't tell your teacher that. Pushing on a teflon insulator generates a current too, but again don;t tell your teacher that. A piece of paper conducts current depending on it's water content, but for all practical purposes it's an insulator.

I need to point out that I challenged an answer to an exam and won. the reason I won: "Your not supposed to know that yet". Make sure you answer questions with the knowledge you were given which may not be the "real answer".

A wire 1mm apart would not conduct electricity, right? Your answer should be that it doesn't conduct electricity. My answer - it depends.

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#### dl324

Joined Mar 30, 2015
12,223
So if I have a 9V battery does that mean positive terminal is +9v and the negative terminal is -9V making the total voltage 18V?

Or is the negative terminal 0V and the positive is +9V making the total voltage 9V?
Neither statement is correct.

A battery has a certain nominal voltage across it's terminals. If one of them is connected to circuit ground, then the voltage at the other terminal will be relative ground.

The nominal voltage of a 9V battery is 9V, regardless of where you place the leads of a multimeter. One direction will read positive, the other direction will read negative.

• narkeleptk

#### sparky 1

Joined Nov 3, 2018
401
I enjoyed this explanation of the common (e-meter) emmiter
It is that once the lecture is over we might leave some details out. It is important to re-enforce what we are taught.
In simulation moving V and I probe on a slightly rearranged layout shown improves the deli very and clarity.
The concept amplifier diagram erased then which type of CE amplifier is given. In this example the first equation is (I sub e).

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#### MrSoftware

Joined Oct 29, 2013
1,956

Is it possible to have both positive and negative voltage in a circuit? Yes if your reference point is somewhere in the middle. Similar to picking the shelf as our reference point, then asking how high is the ceiling and how high is the floor relative the shelf. The ceiling is +2 and the floor is -6, relative the shelf. In a circuit sometimes your reference is in the middle somewhere, and that's how you end up with both positive and negative voltage in a circuit.

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• KeepItSimpleStupid

#### Delta prime

Joined Nov 15, 2019
610
I have a book on electronics "Electronics for dummies" and it says:
Geez... these guys are confusying me.  #### BobaMosfet

Joined Jul 1, 2009
1,292
Hey everyone,

I'm just starting out doing electronics as a hobby in these troubled times and I'm having trouble understanding voltage:

I have a book on electronics "Electronics for dummies" and it says:

"Voltage can be considered positive or negative , but only when compared with some reference point. For example, the voltage at the positive terminal of a flashlight battery is +1.5V relative to the negative terminal. The voltage at the negative terminal is -1.5V relative to the positive terminal."

So if I have a 9V battery does that mean positive terminal is +9v and the negative terminal is -9V making the total voltage 18V?

Or is the negative terminal 0V and the positive is +9V making the total voltage 9V?
No. The actual value of voltage is always between a minimum of two points- one point relative to the other. If the positive is 9V, then we started at zero somewhere. Since the only other place we're comparing is the negative terminal, then it must be zero. Likewise, if we think of the positive terminal as zero, then the negative terminal must be -9V.

In electronics we always chose or create a reference point- this is the only way we have to make a consistent relationship between varying voltages throughout a circuit.

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

#### sparky 1

Joined Nov 3, 2018
401
The teaching of current, it is introduced first. A simpler video, yep all you need is voltage.
What is the stuff at the negative terminal of a battery?

The direction of the current is the same the protons and the battery is the same no games is'nt that right ?

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