Finding the change in mass of a charged body if it loses 1 C

  • #1

Homework Statement


The mass of an electron is 9*10^-31kg. Find the charge in mass of a charged body if it loses 1 Coulomb of negative charge. Use your answer to explain why electricity was originally thought to be weight less.

1 coulomb = 6.642*10^18 elementary charges.

Homework Equations


Everything given in question is above.

The Attempt at a Solution


Since we know that charging of a body depends upon transfer of electrons. So, if a body becomes negatively charged it will gain electrons that is its mass will increase and if a body becomes positively charged it loses electrons hence its mass will decrease. Don’t know where to start with formulas etc. help would be appreciated.
 

Answers and Replies

  • #2
Doc Al
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Here you are losing negative charge, thus losing electrons. How many are lost? What total mass is lost?
 
  • #3
I’m not sure. Are there formulas for it?
 
  • #4
Doc Al
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1 coulomb = 6.642*10^18 elementary charges.
That's one key fact. (Consider an electron to be an elementary charge.)
 
  • #5
I don't understand a lot of physics, but in this question if the body losses 1C of electrons, and 1C of electrons are 6.642E18 electrons, then you has the electron mass above in the statement of problem... Can you now solve this problem?

I do not know if maybe there is an error in my reasoning. ; -)
 
  • #6
That's one key fact. (Consider an electron to be an elementary charge.)
I’m really not sure where to start with calculations, and it’s due tomorrow. If you’ve worked it out how’d you do it?
 
  • #7
Doc Al
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Can you answer this? How many electrons were removed from the charged body?
 
  • #8
Can you answer this? How many electrons were removed from the charged body?
does it lose 6.642*10^-31 electrons?
 
  • #9
if it does how do I find out how much that weighs in kg's?
 
  • #10
Doc Al
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does it lose 6.642*10^-31 electrons?
No. See this:
1 coulomb = 6.642*10^18 elementary charges.

if it does how do I find out how much that weighs in kg's?
Once you get the correct number of electrons, you can make use of the mass of each electron (which is given) to find the total mass.
 
  • #11
What’s the mass of the charged body?
 
  • #12
No. See this:


Once you get the correct number of electrons, you can make use of the mass of each electron (which is given) to find the total mass.
How? I don’t understand
 
  • #13
Alright I got 6*10^-12 is that right ?
 
  • #14
Doc Al
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What’s the mass of the charged body?
That wasn't specified, which makes the problem somewhat ambiguous.

Alright I got 6*10^-12 is that right ?
In kg, that would be correct. (Don't forget units!)

Mass of electrons lost = (Number of electrons lost) X (mass of each electron)

How does that mass compare to the mass of an "everyday" object?
 

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