The electric field strength at any point in an electric field is the force that a 1 C charge would experience at that point.
NOTE
Take care not to confuse the formulae for electrostatic force and electric field strength, though they are related. By
substituting Q2 = 1 C in the formula for electrostatic force, you can go on to calculate electric field strength.
H Electric field strength
The electric field strength (E ), at any point in an electric field can be calculated as:
Electric field strength E = F
___ Q
E = electric field strength (N C–1), F = force (N), Q = charge (C) The unit for electric field strength is N C–1.
Uses and hazards of static electricity
Uses Electrostatic precipitation
As potentially polluting smoke passes through an industrial chimney, it is charged by an EHT of around 50–60 kV (Fig. 20.14). This negatively charges the particles in it.
The charged smoke then passes a positively charged set of plates before it reaches the exterior of the chimney. The ionised particles are attracted to the plates and the smoke is released into the atmosphere after being ‘cleaned’.
smoke particles
2. Smoke particles are attracted to the collecting plates
positively charged collecting plate
waste gases without
1. Smoke particles pick up a negative charge
smoke particles FIG. 20.14 EHT is used to ‘clean’ smoke in industrial chimneys
waste gases containing
3. Collecting plates are knocked to remove the smoke particles
