Electric Fields

Question 0

What is the constant of Coulomb’s law?

Answer 0

1/(4piE0)

= 9*10^9

Question 1

What is Coulomb’s law?

Answer 1

The force between charges is directly proportional to the magnitude of each charge and inversely proportional to the square of the distance separating the charges.

F = k (Q1*Q2)/(r^2)

Question 2

Define electric field strength

Answer 2

The electrostatic force per unit positive charge at a particular point in the field

Question 3

Units of electric field strength?

Answer 3

Newtons per coulombs

Question 4

Derive V= Ed

Answer 4

Work done = QV
F*d             = QV
F/Q            =  V/d
( E = F/Q)
E                = V/d
            V    = Ed

Question 5

Describe charging by induction.

Answer 5

A negatively charged rod repels electrons from an ungrounded objects surface.

The object is grounded and the electrons flow to the earth

Remove ground while maintaining rod in place to prevent electrons returning

Remove charged rod to allow positive charge to spread across objects surface evenly.

Question 6

Describe effects of placing a conducting shape in an electric field

Answer 6

1) induce charges on surface of object
2) electric field inside object will be zero
3) field lines outside object meet perpendicular to its surface in the positive to negative direction

Question 7

Define electrostatic potential

Answer 7

The work done by external forces in moving a unit positive charge from infinity to that point

Question 8

Describe motion of a charged particle in a uniform electric field

Answer 8

No horizontal force and so no horizontal acceleration

Electric force acting vertically. Accelerating particle towards negative plate if positive or positive plate if negative.

Exact trajectory will depend on the mass, charge and speed of particle as well as the separation and voltage of plates.