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.