Chapter 16

Chapter 16

1. Milikan's Oil Drop

   • Charge of Electron
     • The charge on electron was determined by Milikan's Oild Drop Experiment.
     • It was found to be -1.6x10^-19
   • Method
     • The method employed by Milikan was beautifully elegant. By charging tiny drops of oil Milikan planned to find the point at which the force due to the electric field counteracted the force of weight.
     • Due to the known density of the substance used and the fact they were in 'perfect' spheres, all Milikan had to do was apply a known charge to each one. 
     • By changing the strength of the uniform magnetic field Milikan then made these oil drops hover between the plates. As the charge on each one was known, as was its mass, Milikan worked out what force must be acting on the particle to counteract the weight (mg).
     • He found that the data were not continuous, rather there were distinct discrete values. The charge on each oil drop could only take a certain set of values. This was worked out to be the fundamental charge: the charge of an electron.
     • This charge is -1.6x10^-19

2. Charge

   • Key charges
     • Proton=1.6x10^-19
     • Electron=-1.6x10^-19
   • What it is
   • Related equations
   • Representing it

3. Field

   • What it is
     • An electric field is defined as "a region around a charged particle or object within which a force would be exerted on other charged particles or objects."
     • An electric field is created by charged particles or objects
     • In the specification they will either be caused by particles, charged plates or be uniform and of undefined origin.
   • Related Equations
     • Force
       • When charged particles enter an electric field, whether uniform or caused by another particle, they experience a force.
       • The relationships between the force and the particle and fields are seen branching from here.
       • F=(kQq)/r^2
         • This is the force experienced by two particles due to the field created by the other particle
         • k~9x10^9
         • q=charge of first particle
         • Q=charge of second particle
         • r=Distance between particles
         • What this represents
           • The first thing to note is the presence of r^2. This means the relationship is an inverse square law. If the distance doubles, the strength of the electric force due to field is going to decrease by a factor of 4
           • qQ may sound like a noise Fred would make but actually calculates the magnitude of the charge acting. 
           • k is a constant given by the reciprocal of 4 x Pi x permeativitity of free space
           • Put together this can be seen as the magnitude of the charge divided by the effect of the distance between the two particles.
         • E=kQ/r^2
           • E=Electric Field Strength
       • F=qV/d
         • A uniform electric field must occur between two charged plates.
         • When a charged particle enters this field, it will experience a force.
         • The magnitude of this force depends on the strength of the field and the charge on the particle that has entered the field
         • The force can be thought of as the relationship between the charge (q) and the field strength (V/d)
         • This relationship is a 1/x relationship
         • V=p.d. between two plates
         • q=charge on point charge in field
         • d=distance between plates
     • Field
       • E=V/d

4. Relativity

5. Radial Charge

6. Definitions