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The radii of atomic nuclei are of the order of 510-15m. (a) Estimate the minimum uncertainty in the momentum of a proton if it is confined within a nucleus. (b) Take this uncertainty in momentum to be an estimate of the magnitude of the momentum. Use the relativistic relationship between energy and momentum, Eq. (37.39), to obtain an estimate of the kinetic energy of a proton confined within a nucleus. (c) For a proton to remain bound within a nucleus, what must the magnitude of the (negative) potential energy for a proton be within the nucleus? Give your answer in eV and in MeV. Compare to the potential energy for an electron in a hydrogen atom, which has a magnitude of a few tens of eV. (This shows why the interaction that binds the nucleus together is called the 鈥渟trong nuclear force.鈥)

Short Answer

Expert verified
  1. pr=1.510-20kg.m/s
  2. K=3.3210-14J
  3. U=2.08105eV=0.208MeV. This value is about 104larger than the potential energy of an electron in a hydrogen atom.

Step by step solution

01

Use Heisenberg’s Uncertainty Principal

Given that the radius of the atomic nucleus is of the order of 510-15m. We can take the uncertainty in position of the proton inside the nucleus, r=510-15m.

From the Heisenberg鈥檚 Uncertainty Principal for momentum and position,

prrh2.

The uncertainty in momentum will be

prh2rpr1.05510-342510-15pr1.0510-20kg.m/s

So, the uncertainty in the momentum is pr1.0510-20kg.m/s.

02

Use the formula of relativistic relationship

Taking the minimum uncertainty in the momentum of proton as an estimated momentum, p=1.0510-20kgm/s.

Now, solve for E.

E2=1.0510-2031082+1.6710-2731082E2=2.2610-20E=1.510-10J

Using the energy, we can find the value of K.

K=E-mc2K=1.510-10-1.6710-2731082K=3.3210-14J

03

Calculate the potential energy for the proton

For a proton to remain bound to the nucleus, the negative potential energy must be at least equal to the kinetic energy of the proton. Thus,

U=3.3210-141.610-19U=2.08105eVU=0.208MeV

This value is about104 larger than the potential energy of an electron in a hydrogen atom.

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