# Converting from eV/c^2 to kg

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#1

I don't understand the unit eV/c^2 because c is a constant for the speed of light. So shouldn't the unit be more like eV/ms^-1. I have highlighted on the mark scheme where it says conversion of eV or divided by c^2. I don't understand why you only have to do one or the other. Could somebody explain all this please?
0
7 years ago
#2
Because eV (electronvolts) are a unit of energy, they can be converted to mass; all part of particle physics.

Using E=mc^2

E = eV (both are unit of energy) and dividing by c^2 converts it to mass.

Does that help? Energy is commonly converted to mass in particle physics.
0
7 years ago
#3
(Original post by FarmerMan)

I don't understand the unit eV/c^2 because c is a constant for the speed of light. So shouldn't the unit be more like eV/ms^-1. I have highlighted on the mark scheme where it says conversion of eV or divided by c^2. I don't understand why you only have to do one or the other. Could somebody explain all this please?
E=mc2 and since the eV is a unit of energy equal to 1.6x10-19J, m = eV/c2
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#4
This is the method I have used but still wrong :
0.14GeV/c2 = 0.14 x 109eV/c2
0.14 x 109eV/c2 = 2.24 x 10-11 J/c2
2.24 x 10-11 J/c2 = 2.24 x 10-11 Kg
I am right in thinking that a J/c2 is the same as a kg?
0
7 years ago
#5
(Original post by FarmerMan)
This is the method I have used but still wrong :
0.14GeV/c2 = 0.14 x 109eV/c2
0.14 x 109eV/c2 = 2.24 x 10-11 J/c2
2.24 x 10-11 J/c2 = 2.24 x 10-11 Kg
I am right in thinking that a J/c2 is the same as a kg?
You are worrying too much about units and conversion... all you've missed out is that you actually have to put a value in for c2 and do the division, because E/c2 = m (rather than convert the units J/c2 to kg)

Fact: You CAN convert energy to mass. Energy can be converted from eV (one unit) to J (another unit).

If we then divide this by c2 you find the mass (and the unit for this is kg).

I would recommend that you simplify your equation.

0.14GeV = 0.14x109 eV ... simple conversion
0.14x109eV x 1.6x10-19 = 2.24 x 10-11 J (J can now be used in place of E because it is just a measure of energy... same thing) so...

E = 2.24 x 10-11
c = 3x108
so c2 = 9 x 1016 (simple maths)

if E/c2 = m (rearrangement of E=mc2 )
then 2.24 x 10-11 / 9 x 1016 should give you the required answer for the mass... which we know is measured in kg

You left 'c' in the equation as a unit but did nothing with it. You needed to use the value for c to complete the equation. Hopefully this working has shown what you should have done... I can't access a scientific calculator at the moment so haven't checked this but let me know if this does or doesn't help. (I just got my phone working, I get the correct answer)

I'm happy to explain anything that I've not made clear!
4
#6
(Original post by shorty.loves.angels)
You are worrying too much about units and conversion... all you've missed out is that you actually have to put a value in for c2 and do the division, because E/c2 = m (rather than convert the units J/c2 to kg)

Fact: You CAN convert energy to mass. Energy can be converted from eV (one unit) to J (another unit).

If we then divide this by c2 you find the mass (and the unit for this is kg).

I would recommend that you simplify your equation.

0.14GeV = 0.14x109 eV ... simple conversion
0.14x109eV x 1.6x10-19 = 2.24 x 10-11 J (J can now be used in place of E because it is just a measure of energy... same thing) so...

E = 2.24 x 10-11
c = 3x108
so c2 = 9 x 1016 (simple maths)

if E/c2 = m (rearrangement of E=mc2 )
then 2.24 x 10-11 / 9 x 1016 should give you the required answer for the mass... which we know is measured in kg

You left 'c' in the equation as a unit but did nothing with it. You needed to use the value for c to complete the equation. Hopefully this working has shown what you should have done... I can't access a scientific calculator at the moment so haven't checked this but let me know if this does or doesn't help. (I just got my phone working, I get the correct answer)

I'm happy to explain anything that I've not made clear!
Really big thanks all of you. I think I get it, if I think of 0.14x109 eV/c2 as being the same thing as (0.14x109 eV)/c2. It was the eV/c2 and J/c2 that really threw me
0
7 years ago
#7
(Original post by FarmerMan)
Really big thanks all of you. I think I get it, if I think of 0.14x109 eV/c2 as being the same thing as (0.14x109 eV)/c2. It was the eV/c2 and J/c2 that really threw me
Yes. There's really no need to think of it as being /c2 until you plug the eV value into the E=mc2 equation as the 'E'.

Remember, and eV value is just a type of energy value. So you're just converting it to J, and then swapping that for E (energy) once you put into that equation.
0
7 years ago
#8
Oh and while I'm here... don't forget c[SUP2[/SUP] isn't a unit of measurement; it's a value in the equation. So yeah J/ c[SUP2[/SUP] is not a unit.
0
#9
Thanks that is exactly where I was confused. I thought that J/c2 was a unit. I didn't realise c2 was a value in the equation.
1
6 years ago
#10
hi
how do you convert kg to eV/c^2 and vice versa, what are the steps?
thanks
0
6 years ago
#11
(Original post by Shuappz)
hi
how do you convert kg to eV/c^2 and vice versa, what are the steps?
thanks
0
4 years ago
#12
The word either is there for the marker. It is saying that if you do either of these things you will get 1 mark.
1
1 year ago
#13
This measure comes from the Einsteins "mass-energy equivalence" equation, E=mc^2, or rearranging the equation, m=E/c^2
Last edited by Viniciusroro; 1 year ago
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