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 = Q1Q2/4πε₀r^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/4πε₀r^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.

Question 9

Magnitude of electric field strength between plates

Answer 9

E = ΔV/d

Question 10

Electric force on a charge in a uniform electric field

Answer 10

F = qE

Question 11

Equipotential lines/surface

Answer 11

Lines in which points have the same electric potential. No work is done in moving charges along it. Electric field is always perpendicular to equipotential lines

Question 12

Electric potential energy, U

Answer 12

Work done against electric force by an external agent in bringing the point charge from infinity to that point without a net change in kinetic energy.
U = qV

Question 13

Electric potential, V

Answer 13

Work done against electric force per unit positive charge by an external agent in bringing the point charge from infinity to that point without a net change in kinetic energy.
V = U/q

Question 14

Work done in moving an electric charge

Answer 14

qΔV

Question 15

Gradient of U-x graph

Answer 15

Magnitude and direction of electric force

Question 16

Gradient of V-x graph

Answer 16

Magnitude and direction of electric field strength