This uses the concepts of force developed in Stage 1, Subtopic 1.2: Forces and charge in Subtopic 2.1: Potential difference and electric current.
Electrostatically charged objects exert forces upon one another; the magnitude of these forces can be calculated using Coulomb’s Law.
- Solve problems involving the use of:
- Using proportionality, discuss changes in the magnitude of the force on each of the charges as a result of a change in one or both of the charges and/or a change in the distance between them.
- Explain that the electric forces are consistent with Newton’s Third Law.
Video: Elecric Charges : Crash Course
Simulation: Coulomb's Law
When more than two point charges are present, the force on any one of them is equal to the vector sum of the forces due to each of the other point charges.
- Use vector addition in one dimension or two dimensions with right-angled, isosceles, or equilateral triangles to calculate the magnitude and direction of the force on a point charge due to two other point charges.
Video examples: one dimension | right-angled | isosceles | equilateral
Point charges and charged objects produce electric fields in the space that surrounds them. A charged object in an electric field experiences an electric force.
The direction and number of electric field lines per unit area represent the direction and magnitude of the electric field.
- Sketch the electric field lines:
- for an isolated positive or negative point charge and for two point charges
- between and near the edges of two finite oppositely charged parallel plates.
Video: Electric fields with grass seeds
Video: Electric Fields: Crash Course
Simulation: Electric Field
Game: Electric Shocktopus
A positively charged body placed in an electric field will experience a force in the direction of the field; the strength of the electric field is defined as the force per unit charge.
- Solve problems involving the use of:
- Using Coulomb’s Law, derive the formula:
- Solve problems using for one or two point charges in one or two dimensions.
Simulation: Charges and Fields
There is no electric field inside a hollow conductor of any shape, provided that there is no charge in the cavity.
- Sketch the electric field produced by a hollow spherical charged conductor.
• Sketch the electric field produced by charged conductors of an irregular shape.
• Explain how the electric field near sharp points may ionise the air.
Videos: Electric fields - sharp points | Corona and arc discharge demonstration | Pear-shape demonstration