14 Electric Fields

Question 1

Principle of conversation of charge

Answer 1

The sum of all electric charges in any closed system is constant

Question 2

Coulomb’s Law

Answer 2

The magnitude of the electric force between two point charges is directly proportional to the charges and inversely proportional to the square of their separation.
F = Q1Q2/4 π ε₀ r^2

Question 3

ε₀

Answer 3

Permittivity of free space
ε₀ = 8.85x10^-12 m^-3 kg^-1 s^-4 A^-2 (For vacuum/air)

Question 4

Electric field

Answer 4

A region in space where a charge experiences an electric force.

Question 5

Electric field strength

Answer 5

The electric force per unit positive charge placed at that point
E = F(E)/q
Where q is the amount of charge of a small stationary test charge

Question 6

Why must test charge q be small and stationary when calculating electric field strength E

Answer 6

1. A moving charge experiences a magnetic force
2. The charge must be small so that it does not affect the electric field around it. (small in terms of charge not size)

Question 7

Electric field strength near a point charge

Answer 7

E = Q/4 π ε₀ r^2

Question 8

Properties of a conductor in electrostatic equilibrium

Answer 8

1. The electric field inside a conductor is zero
2. The potential inside a conductor is constant
3. Electric field lines are perpendicular to its surface
4. Excess charge resides on the surface of the conductor.