- - magnetic fields (dipoles only)
- gravitational force (monopoles only)
+Gravitational & -ve electric monopoles - field lines radiate towards central object
+Magnetic & electric dipoles - field lines go from + to -, or N to S
+
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## Gravity
- field lines always go from N -> S
- dot means out of page, cross means into page
- ${E_1 \over E_2}={r_1 \over r_2}^2$
+- flux: change in magnetic field
## Electric fields
### Lenz's law
- Right hand grip rule (relationship between directions of $I, F$)
- Eddy currents counter movement within a field
+- Represented by -ve sign in Faraday's law
### Solenoids
- Coil around core (like a transformer but field is transferred to kinetic energy)