# Charge and Field

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• Created by: Taviline
• Created on: 07-12-14 12:00

## Electric Fields

• All charged objects have a field
• Coulomb's Law - formula in book
• If a positive force the particle will be repelled, if a positive force the particles will be attracted
• Use of electric force constant - K
• Inverse square law - as the objects get closer the force becomes stronger at an exponential rate
• Unlike gravity, elecric force can be positive and negative
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## Electric Field Strength

• force for each unit of charge
• N/C
• F=qE
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• Objects with charge at a single point - or can be modeled like that - such as a hollow charge sphere
• At any given point field strength = kQ/r^2 - forumla book
• Inverse square law
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## Electrical Potential Energy

• amount of energy requierd to move an object from infinety to a distance r from the particle
• attracted particles will have a negative value
• Eelec = 0 at infinte distance
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## Electrical Potential

• the amoutn of electrical potential energy per unit of charge
• measured in volts
• Velec
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## Milikan's Oil drop experiment

• found that all charges are some muliple of e
• viscous drag - air resistance
• for an object falling at terminal velocity all forces must be in equilibrium
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## Charge Particles in a Magnetic Field

• Force is acting at a right angle to current
• F=ILB
• F=QVB
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## Motion of a charge particle in an electric field

• CERN uses magnetic fields to bend particles
• circular motion occurs due to a constantly changing current direction
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## Particle Accelerators

• when a charged is acclerated across a potential difference it gains kinetic energy
• KE = qV
• when at high speeds you need the gamma factor
• Etotal = Erest + Ekinetic = gamma * m *c^2
• Linear Accelerators - long evacuate tubes, series of alternating charged electrodes, alternating power supply - as particles are passed through the polarity is changed - electrodes are of increasing length as particle speeds up but AC supply doesn't
• Circular Accelerators - bend particles with magnetic fields , radiate synchrotron energy making them less efficent - tighter circle more energy lost.
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