6.2.1 Point and spherical charges

Electric/electrostatic fields are created by charged objects. 

Electric field strength
The electric field strength of an electric field at a point in space is defined as the force experienced per unit positive charge at that point. We can obtain it using the equation:

E = F/Q

NOTE: F is force experienced by the positive charge Q. The SI unit for electric field strength is N C^-1.

Electric field strength is a vector quantity. Its direction is the direction in which a positive charge would move when placed at that point (away from positive charges/towards negative charges).

Electric field patterns
We use electric field lines/lines of force to map electric field patterns:

• The arrow on an electric field line shows the direction of the field
• Electric field lines are always at right angles to the surface of a conductor
• Equally spaced parallel electric field lines represent a uniform field - one in which the electric field is the same everywhere
• Closer electric field lines represent greater electric field strength

We can model uniformly charged spheres as point charges at the centre. The electric field will be radial (like, sort of circular(?) - a bit like spiders legs around the point charge) and the field strength decreases with distance from the centre.