# What do we mean by the charge on a body is denoted by "q"?

SHASHWAT PRATAP SING
I am sorry if this is a silly question,
we know that-
Electric Charge is a characteristic property of a Subatomic particle.
And, a body is electrically charged by the transfer of electrons.

Then, what does it mean by this the charge on a body is denoted by q.What are we talking here.
Are we deoting this property by q ?
Also, what does it mean when we say a body has charge +2 ? what this +2 has to do with the property electric charge ?

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It is expression of charge quantity as you use x in equation of math. It has unit Coulomb in SI Unit.
Charge has minimum unit called |e|, e is for electron. I guess +2 means charge +2|e|.

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Also, what does it mean when we say a body has charge +2 ?
If it doesn't come with units or context defining the units, "charge +2" is meaningless. +2C is well defined.

Dale
SHASHWAT PRATAP SING
It is expression of charge quantity as you use x in equation of math. It has unit Coulomb in SI Unit.
anuttarasammyak please tell me am I correct ?
This means that suppose a body has the property of electric charge and we measure it and it was found out to be +2C. So, we denote this +2C by q. Thus, this equation q=+2C is the mathematical representation of the above statement.

anuttarasammyak
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Electric charge is a slightly odd case. There is apparently a fundamental unit of charge denoted by |e|, the electronic charge of ##1.6x10^{-19}C##. If someone says "the charge is +3" they mean +3|e|. This is analogous to saying "the speed is 0.5" which means 0.5c. Just shorthand notation everyone agrees to use when convenient.

SHASHWAT PRATAP SING
What does this line mean "the charge on a body".
Does this mean suppose a body has the property of Electric Charge and here we are talking about the magnitude of this charge.

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It really means the excess charge a body. Macroscopic bodies are filled with +/- charges of nearly equal magnitude. The preponderance of one will lead to an excess.

PeroK
SHASHWAT PRATAP SING
It really means the excess charge a body. Macroscopic bodies are filled with +/- charges of nearly equal magnitude. The preponderance of one will lead to an excess.
hutchphd please tell me am I right ?
So, Basically this line-->"the charge on a body" means the amount of charge on a body or the numeric value of charge on a body. Right ?
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the numeric value of charge on a body.
And after measuring this propety ,We denote this amount of charge(numeric value) by q. Which would be of the form q = ± ne.

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hutchphd please tell me am I right ?
So, Basically this line-->"the charge on a body" means the amount of charge on a body or the magnitude of charge on a body. Right ?
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the magnitude of charge on a body.
We denote this amount of charge(magnitude) by q .
https://en.wikipedia.org/wiki/Electric_charge

It really means the excess charge a body. Macroscopic bodies are filled with +/- charges of nearly equal magnitude. The preponderance of one will lead to an excess.
hutchphd please tell me am I right ?
So, Basically this line-->"the charge on a body" means the amount of charge on a body or the magnitude of charge on a body. Right ?
You are ignoring the key emphasis (bold) in the response you got. And what do you mean by magnitude? Charge can be negative.

SHASHWAT PRATAP SING
You are ignoring the key emphasis (bold) in the response you got. And what do you mean by magnitude? Charge can be negative.
A.T. I know that charge can be negative.By saying magnitude I am taking about the numeric value of charge or amount of the charge.
I am just saying that in this line-->"the charge on a body" means the amount of charge on a body or the numeric value of charge.

SHASHWAT PRATAP SING
PeroK, please tell me am I right here ?
So, Basically this line-->"the charge on a body" means the amount of charge on a body or the numeric value of charge on a body. Right ?
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the numeric value of charge on a body.
And after measuring this propety ,We denote this amount of charge(numeric value) by q.

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PeroK, please tell me am I right here ?
So, Basically this line-->"the charge on a body" means the amount of charge on a body or the numeric value of charge on a body. Right ?
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the numeric value of charge on a body.
And after measuring this propety ,We denote this amount of charge(numeric value) by q.
I don't know that there is a difference between "amount" and "numeric value" in this case. If ##q## is the charge, then ##q## can be positive or negative. Those being the two types of charge found in nature.

This is one way electromagnetism is different from gravity: there is only positive mass; whereas, there are positive and negative charges.

SHASHWAT PRATAP SING
I don't know that there is a difference between "amount" and "numeric value" in this case. If ##q## is the charge, then ##q## can be positive or negative. Those being the two types of charge found in nature.

This is one way electromagnetism is different from gravity: there is only positive mass; whereas, there are positive and negative charges.
PeroK I think you didn't understand my question.

My question is What does this line mean "the charge on a body" ?

for which I am asking that have I understood the concept ?
So, Basically this line-->"the charge on a body" means the amount of charge on a body or the numeric value of charge on a body. Right ?
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the numeric value of charge on a body.
And after measuring this propety ,We denote this amount of charge(numeric value) by q.
which would be of the form q = ± ne.

I know that charge can be positive and negative. For that I have also edited my question.

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PeroK I think you didn't understand my question.

My question is What does this line mean "the charge on a body" ?

for which I am asking that have I understood the concept ?
So, Basically this line-->"the charge on a body" means the amount of charge on a body or the numeric value of charge on a body. Right ?
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the numeric value of charge on a body.
And after measuring this propety ,We denote this amount of charge(numeric value) by q.

I know that charge can be positive and negative. For that I have also edited my question.
Yes, but most people would be happy with "Let ##q## be the charge on a body." You don't have to measure it because ##q## can be a variable. The same as any other variable, like mass and velocity and length.

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SHASHWAT PRATAP SING
SHASHWAT PRATAP SING
PeroK, then what does this line mean -->the charge on a body is denoted by "q"?

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PeroK, then what does this line mean -->the charge on a body is denoted by "q"?
I believe you're expected to understand a statement like that without a more fundamental analysis - certainly a physics textbook author would expect that statement to be self-explanatory.

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"The charge on a body"...

In principle, this is a number, a signed integer equal to the number of positive charged particles in the body minus the number of negatively charged particles in the body.

In practice, for bodies larger than tiny atomized drops of oil the charge will be a large number. Large enough that we can divide by about 6 x 1018 to get a much more usable number -- the number of Coulombs of charge the body has.

So a body with an excess of 6 x 1018 positive elementary charges will have a charge of approximately one Coulomb.

When we say that this is "denoted by 'q'" we just mean that we are going to use the variable name "q" to denote the charge on the object. So for the above object, q would be 1 Coulomb.

There is nothing physically meaningful about the choice of the letter q. It is just a handy conventional choice. As long as everyone uses "q" to denote an amount of charge, it is easy to read equations and not get confused worrying that "q" might instead be used to denote time, distance, mass or temperature.

SHASHWAT PRATAP SING
SHASHWAT PRATAP SING
jbriggs444 Please tell me am I correct here -
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the numeric value of charge on a body.
And after measuring this propety ,We denote this amount of charge(numeric value) by q. Which would be of the form q = ± ne.
So, when we say this line--> "charge on the object" means thatwe are talking about the amount of charge on a body. It is this Which we denote by q.
That's why we say this line that -->The charge on a body denoted by 'q' .

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jbriggs444 Please tell me am I correct here -
Suppose a body has the property of Electric Charge and we intend to measure this property.So, by saying this line-->"the charge on a body" we mean that we are talking about the amount of charge on a body or the numeric value of charge on a body.

"The charge on a body".
"The body's charge".
"The numeric value of charge on a body".

All are synonymous. They mean the same thing. [Though one might quibble that the last one needs units to make it truly synonymous].

Like mass, height, volume, density, length, temperature, location or velocity, charge is a value that quantifies some aspect of an object. It is a property of the object.

And after measuring this propety ,We denote this amount of charge(numeric value) by q. Which would be of the form q = ± ne.
I do not know what you mean to say here. The variable q will have a numeric value. That value may be positive, negative or zero. We would probably choose to express that value as a number and a unit of measure.

For instance "q = 1 elementary charge"
or "q = -0.3 Coulomb".

That's why we say this line that -->The charge on a body denoted by 'q' .
We say that because it establishes an abbreviation. We can then use the letter q because it is clumsy to fill in equations with "the charge on the body" when we could put in "q" instead.

$$\text{The Force of the first body on the second body} = \text{Coulomb's Constant}\frac{\text{The charge of the first body} \times \text{The charge of the second body}} {\text{The distance between the two bodies}^2}$$

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SHASHWAT PRATAP SING
jbriggs444 my question is this only I want to know that what does this line -->The charge on a body denoted by q mean ?
and as you said-
"The charge on a body".
"The numeric value of charge on a body".
"The body's charge".
All are synonymous. They mean the same thing.

Ok, so this line--> The charge on a body denoted by q means here we are talking about the amount of charge on a body.
So, q denotes the amount of charge on a body which is of the form --> q= ± ne
and we can choose to express that value as a number and a unit of measure.

Suppose If we are given this equation q=+2C , so this means that a body has the property of electric charge and the amount of electric charge this body has is +2C, Which is represented by q.
so, we write q= +2C
Am I correct now ?

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So, q denotes the amount of charge on a body which is of the form --> q= ± ne
I do not agree with this. One would never write "q= ± ne"

The ± symbol means that there are two possibilities. Either q = +ne or q = -ne. But if "ne" is the number of excess elementary charges on the object then there is only one possibility: q=ne [elementary charge units].

ne might be positive or it might be negative. But there is no need to indicate this with a leading ±. Doing so is erroneous.
Suppose If we are given this equation q=+2C , so this means that a body has the property of electric charge and the amount of electric charge this body has is +2C, Which is represented by q.
so, we write q= +2C
Am I correct now ?
Yes, I think I agree with this. But we started with "q=+2C" and we ended with "q=+2C". That's a tautology.

SHASHWAT PRATAP SING
jbriggs444 by q= ± ne
I mean that if a body is positively charged we will write q=ne
and if the body is negatively charged we will write q=-ne

But , yes you are right we will write q=ne and proper signs will be used while taking the values as ne might be positive or it might be negative. There is no need to indicate this with a leading ±

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jbriggs444 by q= ± ne
I mean that if a body is positively charged we will write q=ne
and if the body is negatively charged we will write q=-ne
As it seems you realize now,

If the body is positively charged then ne is positive and q=ne.
If the body is negatively charged then ne is negative and q=ne.
If the body has zero charge then ne is zero and q=ne.

SHASHWAT PRATAP SING
So jbriggs444, tell me have I now understood the concept correctly ?

Ok, so this line--> "The charge on a body is denoted by q" means here we are talking about the amount of charge on a body.
So, q denotes the amount of charge on a body which is of the form --> q= ne

and we can choose to express that value as a number and a unit of measure.

Suppose If we are given this equation q=+2C , so this means that a body has the property of electric charge and the amount of electric charge this body has is +2C, Which is represented by q.
so, we write q= +2C

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So jbriggs444, tell me have I now understood the concept correctly ?

Ok, so this line--> "The charge on a body is denoted by q" means here we are talking about the amount of charge on a body.
So, q denotes the amount of charge on a body which is of the form --> q= ne

and we can choose to express that value as a number and a unit of measure.

Suppose If we are given this equation q=+2C , so this means that a body has the property of electric charge and the amount of electric charge this body has is +2C, Which is represented by q.
so, we write q= +2C
What is "ne" supposed to mean? You keep using the term without definition.

Also, if we are given that q=+2C then we do not need any physical reasoning whatsoever to conclude that q=+2C.

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here, n means the number of electrons transferred and e is the elementary charge. So, q = ne tells us about the quantisation of charge.
Number transferred? That has little to do with the number that are there now. "q" conventionally denotes the net charge that is there now.

If n is the excess number of electrons currently on an object and e is the unit of one [positive] elementary charge then then the correct formulation would be q=-ne

SHASHWAT PRATAP SING
here, n means the number of electrons transferred and e is the elementary charge. So, q = ne tells us about the quantisation of charge.
Sorry, jbriggs444 I have written wrong. So, I have deleted that post.
q=ne this means that the charge on a body(q) is integral multiple of a basic unit of charge (e).

Also, if we are given that q=+2C then we do not need any physical reasoning whatsoever to conclude that q=+2C

jbriggs444 here I am just telling that what does q= +2C mean.

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Sorry, jbriggs444 I have written wrong. So, I have deleted that post.
q=ne this means that the charge on a body(q) is integral multiple of a basic unit of charge (e).
Here "q" is the charge on the body, "n" is the net excess of positive elementary charges on the body and "e" is a unit of charge equal to one elementary charge (i.e. the charge of one proton).

Yes.

So, for instance, a pith ball with deficit of 6 x 1017 electrons would have charge q equal to +6 x 1017 e or approximately +0.1 Coulombs.

[I suspect that is a rather enormous charge for a pith ball]

SHASHWAT PRATAP SING
So jbriggs444, tell me have I now understood the concept correctly ?

Ok, so this line--> "The charge on a body is denoted by q" means here we are talking about the amount of charge on a body.
So, q denotes the amount of charge on a body which is of the form --> q= ne

and we can choose to express that value as a number and a unit of measure.

Suppose If we are given this equation q=+2C , so this means that a body has the property of electric charge and the amount of electric charge this body has is +2C, Which is represented by q.
so, we write q= +2C

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Sorry, jbriggs444
jbriggs444 here I am just telling that what does q= +2C mean.

What does the m=10kg mean?
The charge of "something" (say a body) is physical property in the same way that mass or volume are properties.
It is pointless to try to "explain" this by thinking about the number of charged elementary particles. You would presumably not try to "explain" the mass of a body by saying that it is the number of atoms multiplied by some constant, or?

Also, there is not need for the total charge to be a multiple of e, there are lots of situations where this is not tru; for example because of screening or because you are measuring say the average value of a dynamic process.
See e.g. single electron transistors (SETs) or Coloumb blockade.

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SHASHWAT PRATAP SING
What does the m=10kg mean?
The charge of "something" (say a body) is physical property in the same way that mass or volume are properties.
It is pointless to try to "explain" this by thinking about the number of charged elementary particles. You would presumably not try to "explain" the mass of a body by saying that it is the number of atoms multiplied by some constant, or?

I now this that-
Electric Charge is a characteristic property of Subatomic particles.

what does it mean by this line--> the charge on a body is denoted by q.

and for this I have written-

Ok, so this line--> "The charge on a body is denoted by q" means here we are talking about the amount of charge on a body.
So, q denotes the amount of charge on a body which is of the form --> q= ne

and we can choose to express that value as a number and a unit of measure.

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I observe your statement is clear. I have no other interpretation.

SHASHWAT PRATAP SING
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I now this that-
Electric Charge is a characteristic property of Subatomic particles.]

That depends on what you mean . It is of course true that charge ultimately comes from subatomic particles, but there are -as was mentioned above- many situation where the charge you can detect and measure comes from for example quasiparticles and exctions and since these are many-body effects you shouldn't (and mostly can't) relate their charge to subatomic particles (this is the reason for why quasiparticles can have fractional charges less than that of a single electron)
So, q denotes the amount of charge on a body which is of the form --> q= ne
Again, this is not usually correct. Charge is usually a continuous variable (it is actually quite difficult to experimentally realize a situation where charge is quantised ) and can take any value, not just multiples of e.

See e.g. the spectrum of a Cooper pair box or a charge qubit if you want to see some experimental data.