1. B Fe H Fe B gap H gap B air H air i coil windings gap region iron core

2. width L thickness t area A q = - e electrons are the charge carriers in copper

3. + + + + + + + + + - - - - - - - - - dy F +q+q -q-q

4. Induced dipole moment – helium atom -e +2e Zero electric field – helium atom symmetric  zero dipole moment -e +2e -e A B effectively charge +2e at A and -2e at B dipole moment p = 2 e d

5. -q-q +q+q r 1  r – (d/2)cos  r 2  r + (d/2)cos  r  P ErEr EE (d/2)cos 

6. + + + + + + + + + - - - - - - - - - +f+f -f-f     dA -b-b +b+b

7. +q+q -q-q