# Binding Energy

#1
I'm very confused about the concept of mass to energy, energy being "given out", yet still being the energy that holds together the constituent nucleons which form the nucleus.

Here is my understanding at the moment:

When nucleons or nuclei fuse together to form a nucleus, mass is lost - this mass is "transferred" to the energy of the new nucleus, which is given out and is the energy which holds together the nucleus.

Therefore, to break a nucleus apart into its individual nucleons, we have to put in the same amount of energy which is currently holding together the nucleus, to overcome it.

Is this correct?
0
7 years ago
#2
(Original post by minnigayuen)

Here is my understanding at the moment:

When nucleons or nuclei fuse together to form a nucleus, mass is lost - this mass is "transferred" to the energy of the new nucleus, which is given out and is the energy which holds together the nucleus.
No. The energy is just given out as heat, or gamma rays to be more direct.
The force which holds nucleons together is something called the strong nuclear force. It has a really small range, so the nuclei have to get really close together, but once they do it acts like a hook. Because the nuclei have to get so close together, they have to overcome their electrostatic repulsion (cos the nuclei are positive), and this is why there's such a large energy input required (activation energy).
(Original post by minnigayuen)
Therefore, to break a nucleus apart into its individual nucleons, we have to put in the same amount of energy which is currently holding together the nucleus, to overcome it.
In theory, to break the nucleus apart again you would have to supply the same amount of energy released by the lost mass when fusion occurred as well as enough energy to undo the strong nuclear attraction, but taking into account the repulsion of the protons? In that respect your initial claim about energy being transferred to the forces holding the new nucleus together is partially right. It's kinda like an astronomical object wandering into the gravitational field of a planet, you don't think of it having any gravitational potential energy, but once it goes near the planet it suddenly does. Maybe you think of the small nucleus as having "potential nuclear energy"? It gets really complicated and well outside the spectrum of my A level physics knowledge.
In summary:
During fusion, mass is lost, giving out energy in the form of electromagnetic rays.
2
#3
(Original post by TheSK00T3R)
No. The energy is just given out as heat, or gamma rays to be more direct.
The force which holds nucleons together is something called the strong nuclear force. It has a really small range, so the nuclei have to get really close together, but once they do it acts like a hook. Because the nuclei have to get so close together, they have to overcome their electrostatic repulsion (cos the nuclei are positive), and this is why there's such a large energy input required (activation energy).

In theory, to break the nucleus apart again you would have to supply the same amount of energy released by the lost mass when fusion occurred as well as enough energy to undo the strong nuclear attraction, but taking into account the repulsion of the protons? In that respect your initial claim about energy being transferred to the forces holding the new nucleus together is partially right. It's kinda like an astronomical object wandering into the gravitational field of a planet, you don't think of it having any gravitational potential energy, but once it goes near the planet it suddenly does. Maybe you think of the small nucleus as having "potential nuclear energy"? It gets really complicated and well outside the spectrum of my A level physics knowledge.
In summary:
During fusion, mass is lost, giving out energy in the form of electromagnetic rays.
Ah okay thank you so much! So where does this "binding energy" come from - does more just 'form' when more nucleons become close enough to feel the strong nuclear force? Also, is the binding energy the same as the strong nuclear force then, or is it just the concept of the quantity of energy.

I feel like i'm completely misinterpreting what binding energy is Sorry if it sounds like i haven't picked up anything from what you've explained, i'm having quite a lot of trouble getting my head around this.
0
7 years ago
#4
(Original post by minnigayuen)
Ah okay thank you so much! So where does this "binding energy" come from - does more just 'form' when more nucleons become close enough to feel the strong nuclear force? Also, is the binding energy the same as the strong nuclear force then, or is it just the concept of the quantity of energy.

I feel like i'm completely misinterpreting what binding energy is Sorry if it sounds like i haven't picked up anything from what you've explained, i'm having quite a lot of trouble getting my head around this.
When nucleons are under the attraction of the strong nuclear force, it does a huge amount of work on the nucleons to combine them.
You need a huge amount of energy to fire 2 nucleons e.g 2 protons, together so that they have enough energy to overcome the electrostatic force of repulsion.
Once they are close enough, about 3-4 fm then the strong residual force is able to do work on the nucleons, the nucleons lose potential energy.
When systems go from higher potential energy to lower potential energy, energy is released just like how water drops from a cliff; losing GPE.
This loss of energy is in form of mass.
0
7 years ago
#5
(Original post by minnigayuen)
Ah okay thank you so much! So where does this "binding energy" come from - does more just 'form' when more nucleons become close enough to feel the strong nuclear force? Also, is the binding energy the same as the strong nuclear force then, or is it just the concept of the quantity of energy.

I feel like i'm completely misinterpreting what binding energy is Sorry if it sounds like i haven't picked up anything from what you've explained, i'm having quite a lot of trouble getting my head around this.
The binding energy is the energy released when the new nucleus forms.
In simple terms (I'm assuming you're an A level student) all you have to know is that when two nuclei fuse together, the mass of the new nucleus is lower than the total mass of the reactant nuclei. You may have learnt in GCSE chemistry that all neutrons and protons have the same mass; this isn't quite right, as the mass of them decreases ever so slightly the bigger the nucleus that they're in.
So where has the mass gone?
Einstein says that E=mc^2, so this mass must have been converted to energy. The energy released is the binding energy.
This process is what allows humans to make horrible things like hydrogen bombs, and it's what allows the sun to make nice things like light.
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