physics / fields.mdon commit [english] start Ransom & Invictus notes (b0fa307)
   1# Fields
   2
   3**Non-contact force**
   4
   5Types of fields:
   6- gravitational
   7- electric
   8- magnetic
   9
  10Electric and magnetic fields are the two components of the electromagnetic field (effectively the same force). Permeates the universe.
  11
  12Field diagrams - N to S (current +ve to -ve)
  13
  14
  15Field strength - inverse sq law
  16
  17## Gravitational fields
  18
  19### Field strength
  20
  21$$g={{F_g} \over m}$$
  22
  23## Electric fields
  24
  25### Field lines
  26- +ve to -ve
  27- start and end $\perp$ to surface
  28- never cross
  29
  30### Field strength
  31
  32$$E = {F \over q}$$
  33
  34
  35
  36
  37## Transformers
  38
  39Primary - input
  40Secondary - output
  41
  42As $V \Rightarrow \infty, P_{loss} \Rightarrow 0$
  43
  44$$P_{loss} = I^2 R$$
  45
  46where $R$ is determined by resistivity per length of cable
  47
  48Therefore, power loss is proportional to the square of current.
  49
  50Electronmagnetism & electromagnetic induction
  51
  52Changing magnetic field generates current & vice versa
  53
  54Only for AC, because DC voltage is constant, so does not generate magnetic field
  55
  56Output is proportional to ratio primary : secondary
  57
  58
  59$${V_{sec} \over V_{pri}} = {turns_{sec} \over turns_{pri}}$$
  60
  61Iron - good conductor of magnetic fields. Used as a core.