# Converting from eV/c^2 to kg

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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?

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#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.

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.

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#3

(Original post by

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?

**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?

^{2}and since the eV is a unit of energy equal to 1.6x10

^{-19}J, m = eV/c

^{2}

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This is the method I have used but still wrong :

0.14GeV/c

0.14 x 10

2.24 x 10

I am right in thinking that a J/c

0.14GeV/c

^{2}= 0.14 x 10^{9}eV/c^{2}0.14 x 10

^{9}eV/c^{2}= 2.24 x 10^{-11}J/c^{2}2.24 x 10

^{-11}J/c^{2}= 2.24 x 10^{-11}KgI am right in thinking that a J/c

^{2}is the same as a kg?
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#5

(Original post by

This is the method I have used but still wrong :

0.14GeV/c

0.14 x 10

2.24 x 10

I am right in thinking that a J/c

**FarmerMan**)This is the method I have used but still wrong :

0.14GeV/c

^{2}= 0.14 x 10^{9}eV/c^{2}0.14 x 10

^{9}eV/c^{2}= 2.24 x 10^{-11}J/c^{2}2.24 x 10

^{-11}J/c^{2}= 2.24 x 10^{-11}KgI am right in thinking that a J/c

^{2}is the same as a kg?^{2}and do the division, because E/c

^{2}= m (rather than convert the units J/c

^{2}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 c

^{2}you find the mass (and the unit for this is kg).

I would recommend that you simplify your equation.

0.14GeV = 0.14x10

^{9}eV ... simple conversion

0.14x10

^{9}eV 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 = 3x10

^{8}

so

**c**(simple maths)

^{2}= 9 x 10^{16}if E/c

^{2}= m (rearrangement of E=mc

^{2})

then

**2.24 x 10**should give you the required answer for the mass... which we know is measured in kg

^{-11}/ 9 x 10^{16}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!

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(Original post by

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 c

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 c

I would recommend that you simplify your equation.

0.14GeV = 0.14x10

0.14x10

c = 3x10

so

if E/c

then

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'm happy to explain anything that I've not made clear!

**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 c

^{2}and do the division, because E/c^{2}= m (rather than convert the units J/c^{2}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 c

^{2}you find the mass (and the unit for this is kg).I would recommend that you simplify your equation.

0.14GeV = 0.14x10

^{9}eV ... simple conversion0.14x10

^{9}eV 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 = 3x10

^{8}so

**c**(simple maths)^{2}= 9 x 10^{16}if E/c

^{2}= m (rearrangement of E=mc^{2})then

**2.24 x 10**should give you the required answer for the mass... which we know is measured in kg^{-11}/ 9 x 10^{16}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!

^{9}eV/c

^{2}as being the same thing as (0.14x10

^{9}eV)/c

^{2}. It was the eV/c2 and J/c2 that really threw me

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#7

(Original post by

Really big thanks all of you. I think I get it, if I think of 0.14x10

**FarmerMan**)Really big thanks all of you. I think I get it, if I think of 0.14x10

^{9}eV/c^{2}as being the same thing as (0.14x10^{9}eV)/c^{2}. It was the eV/c2 and J/c2 that really threw me**/c**until you plug the eV value into the E=mc

^{2}^{2}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.

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#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.

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Thanks that is exactly where I was confused. I thought that J/c

^{2}was a unit. I didn't realise c^{2}was a value in the equation.
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#11

(Original post by

hi

how do you convert kg to eV/c^2 and vice versa, what are the steps?

thanks

**Shuappz**)hi

how do you convert kg to eV/c^2 and vice versa, what are the steps?

thanks

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#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.

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#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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