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8/28/00 NE 409

- Relativistic Dynamics
- Electromagnetic Fields
- What happens if the electric (E) and Magnetic (B) fields are in a moving reference frame?

- Electromagnetic Fields

Lorentz force in S frame frame

q = (E + VxB) = 0

Motion in S’ frame frame

- Suppose that S’ is chosen so that it moves in the direction of the particle motion with a velocity equal to the particle velocity. In the S’ frame the particle appears to be stationary.
- Here, the VxB term in the Lorentz equation is zero.

Since the force equal zero in both the S and S’ frame frame

- E = 0 in the S’ frame.
- Conclusion
- E and B look different to observers in different frames of reference. E and B are related depending upon the motion of the reference frame. This is why we call E and B electromagnetic fields rather than electric and magnetic fields.

Transformation of electric and magnetic fields from S’ to S frame of reference

- E’|| = E||
- E’ ^= g( E ^+U x B^)
- B’|| = B||
- B’ ^= g( B ^- U x E^/c2)

Summary S frame of reference

- Newtonian mechanics is a specific case of relativistic mechanics (u << c).
- Special relativity assumes that all inertial frames of reference are equivalent
- General relativity assumes that all possible reference frames are equivalent.

Mass Defect S frame of reference

- Radius of atom is about 1 angstrom. This is about 0.1 nanometer.
- Radius of a nucleus is about 10-5 angstroms. This is about 10-15 meters.
- Atomic Number = Z, is the number of electrons or protons in an atom.
- Atomic Mass = A, is the mass in Atomic Mass Units (AMU)

More facts S frame of reference

- A is about equal to the number of protons plus the number of neutrons in an atom.
- Mass of electron = me = 0.511 MeV/c2 or 9.11x10-31 kg.
- Mass of proton = mp = 938.3 MeV/c2 or 1.673x10-27 kg.
- Mass of neutron = mn = 939.6 MeV/c2 or 1.675x10-27 kg.

Even More Facts S frame of reference

- Number of Neutrons = N
- A = Z + N

Mass Deficit for Oxygen S frame of reference

Differential Mass S frame of reference

The resulting mass change must go into energy according to the mass energy relationship,

Binding Energy S frame of reference

- This energy is known as the binding energy. In order to break apart the atom into its basic components, you would need to put in an energy equivalent to the binding energy of the atom.
- Binding Energy per Nucleon = Dmc2/A

Quantum Mechanics S frame of reference

- The second great development in modern physics is quantum mechanics.
- Quantum mechanics was developed to describe the behavior of atoms.

Questions? S frame of reference

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