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G485 Fields, Particles and the Frontiers of Physics
Electric and Magnetic Fields

Electric Fields
Electric fields are created by electric charges. If a charged particle ventures into this electric field, then it
will experience a force. The magnitude of which depends of the charge and strength of the electric field.…

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Comparing electric and gravitational fields, the similarities are:
- Both electric and gravitational fields are to do with `action at a distance'
- Field strengths follow an inverse square law with distance.
- A point mass and point charge both produce radial fields
- Field strength is defined as force…

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Moving charges in a magnetic field
A current-carrying wire placed in a magnetic field experiences a force because each moving electron
within the wire experiences a tiny force.

Consider the force F on a positive particle moving is at right angles to the magnetic field.
= where B is the…

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An e.m.f is induced in a circuit whenever there is a change in the magnetic flux linkage. The
magnitude of the induced e.m.f in a circuit can be determined using Faraday's law of
electromagnetic induction;
The magnitude of the induced e.m.f is equal to the rate of change of Magnetic…

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Capacitors

Properties

A capacitor consists of two metal plates separated by insulation. When connected to a source of e.m.f., the
plates acquire equal but opposite charges. The positive plate loses electrons and the negative plate gains
an equal number of electrons.

The magnitude of the charge Q on one of…

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Example
A 0.02F capacitor is charged to 9V. The fully charged capacitor is discharged through a lamp in a time of 40
ms. Find the average power dissipated by the lamp.
E = 0.5CV2 = 0.5x0.02x9 = 0.81J. Power= Work/Time => Power = 0.81/(40x10-2) = 20W


Capacitor discharging through a…

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Nuclear Physics

The nuclear atom structure
- Rutherford carried out the electron scattering experiment. Alpha particles were targeted towards a
thing gold foil. The number of alpha particles scattered at various angles were counted using a
alpha particle detector.
Most of the alpha particles weren't scattered The gold atoms are…

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- A proton has two up quarks and 1 down quark; (u u d)
- A neutron has one up quark and two down quarks; (u d d)
- A pi+ meson has one up quark and one down antiquark; (u )
You can hence work out the charge, baryon…

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Stable nuclei lie on the line of stability. The nuclei in the shaded region are unstable. Decay of an unstable
nucleus brings it close to the line of stability.



Alpha decay
A helium nucleus is emitted;
232 228 4
90 88 + 2


Beta-minus decay
Electron-rich nuclei emit an electron…

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Nuclear Binding energy
The mass-energy equation is
= 2
where is the change in energy of the system, is the change in mass of the system and = 3x108ms-1.
Consequence of this:
- The mass of a system increases when external energy is supplied to the system.
- Energy is…

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