SJPO Electric Field

Coulomb’s Law for Mutual Electric Force

F = (kq1q2) / r²

Q = charge [C]

r = distance between 2 charges

k = 1 / (4πε0)

What is e, the elementary charge

Smallest quantity of charge that can exist separately, 1.60 × 10^-19

Q = ne

Formula for electric field strength / intensity

E = F / Q

F = force (N)

Q = charge (C)

SI unit is N C-1

OR

E = [1 / (4πε0)] [Q / r²]

r = distance of separation between charges

What is k, 1 / (4πε0)

ε0, permittivity of free space = 8.85 × 10^-12

Hence k = 8.99 × 10^9

Define electric potential (V)

Work done by an external agent in moving unit positive charge from infinity to the point without change in kinetic energy

Formula for electric potential

V = w.d. / Q

Formula for electric potential due to point charge (electric potential at a distance r from the centre of Q)

V = [1 / (4πε0)] [Q / r]

*Q is substituted with its sign

Define electric potential energy

Work done by an external agent in moving a charge from infinity to that point without change in kinetic energy

Define electric potential difference

• Potential difference between 2 points in an electric field region

• Work done per unit positive charge when a small test charge is moved between those 2 points

Define equipotential surface

Imaginary surface formed by points equidistant from a charge hence having the same electric potential

• No change in potential in moving a charge along the surface hence no work is done

Formula for magnitude of electric field strength between 2 charged parallel plates

E = ∆V / d

Formula for force on a charge Q in an electric field between 2 charged parallel plates

F = (Q∆V) / d

d = distance between plates

Formula for acceleration on a charge Q in an electric field between 2 charged parallel plates

a = (Q∆V) / (md)

m = mass of charged

d = distance between plates

mass of electron

m = 9.1 × 10^-31