Charge is measured in coulombs, and one coulomb is a lot of charge

1. The symbol for charge is $Q$ and the unit is the coulomb, written $C$.
2. The charge on one electron is only about $1.6\times 10^{-19}C$, so a single coulomb represents an enormous number of electrons.
3. The static charge left on a rubbed polythene rod is a few nanocoulombs, around $10^{-9}C$, which is why it lifts scraps of paper but nothing heavier.
4. By contrast a torch bulb drawing $0.30A$ moves $0.30C$ past every point each second, so a working circuit shifts far more charge than static electricity ever does.

An electric field is the region where a charge feels a force

1. Bring any charge into that region and it is pushed or pulled, with nothing touching it.
2. The field is strongest close to the charge producing it and weakens as you move away.
3. The idea runs parallel to the magnetic field, with one substitution: the thing that feels the force is a charge rather than a magnetic pole.
4. Field lines are drawn the same way too: their shape shows the field, their arrows show its direction, and their spacing shows its strength.

Field direction is the direction of the force on a positive charge

1. The direction of an electric field at a point is the direction of the force on a positive charge placed at that point.
2. That single rule fixes every arrow you will ever draw: lines point away from positive charge and towards negative charge.
3. A negative charge sitting in the field feels a force in the opposite direction to the field line through it.
4. Electric field lines never cross, for the same reason as magnetic ones: the force at a point has only one direction.

A point charge and a charged sphere both give a radial field

1. Around an isolated point charge the field is radial: straight lines spreading out evenly in all directions.
   1. For a positive charge the arrows point outwards, away from the charge.
   2. For a negative charge the arrows point inwards, towards the charge.
   3. The lines spread further apart with distance, which is the picture of the field getting weaker.
2. Around a charged conducting sphere the pattern outside is identical to that of a point charge sitting at its centre.
   1. Draw the radial lines starting at the surface of the sphere and leaving it at right angles, not from a dot in the middle.
   2. The charge spreads evenly over the outer surface, because like charges repel and push each other as far apart as they can get.

Parallel plates give a uniform field of equally spaced lines

1. Two flat metal plates held close together and given opposite charges produce a uniform field in the region between them.
2. The lines are straight, parallel and evenly spaced, running from the positive plate across to the negative plate.
3. They meet both plates at right angles, so draw them perpendicular to the plate surfaces.
4. Even spacing is the whole point, because it says the field has the same strength everywhere between the plates.
5. Draw only the region between the plates and stop at their edges, since the way the field bulges at the ends is not examined.