QCEphysics

Electrostatics

define Coulomb's Law and recognise that it describes the force exerted by electrostatically charged objects on other electrostatically charged objects

- Coulomb's law states that like electric charges repel and opposite electrical charges attract, with a force proportional to the product of the electric charges and inversely proportional the square of the distance between them

• The sign of the charges must be included - positive force values means repulsion and negative force value means attraction

solve problem involving Coulomb's law

- Labelling forces

○ The force on A due to B - FAB

define the terms electric fields, electric field strength and electrical potential energy

- Electric field is a region of space near an electrically charged particle or object within which a force would be exerted on other electrically charged particles or objects

   • Key features in electric field diagrams include:

▪ Electric field lines never cross

▪ Electric field lines are directed from positive charge to negative charge

▪ Electric field lines will enter or leave any charged surface at right angles

▪ Number of lines per unit area represents the electric field strength

▪ Closer the lines, higher the field strength

▪ Electric fields radiate in 3D space, but is represented as 'cross-sectional' diagrams

- Electric field strength is the intensity of an electric field at a particular location (NC-1)

• In a uniform electric field - there is constant field strength between charged parallel plates

 • If a positive particle is fired into the field at constant speed, it would deflect the particle from the horizontal path (the bigger the force, the greater the deflection)

- Electrical potential energy is the capacity of electric charge carriers to do work due to their position in an electric field (J)

• If charge is moved perpendicular to the field lines then no work will be done
• The work done in moving charge +q will store electrostatic potential energy . If the repulsive force between the charges is allowed to act by itself, then the stored electrical potential energy will be converted back to kinetic energy of motion as the particles fly away from each other.

solve problems involving electric field strength

solve problems involving the work done when an electric charge is moved in an electric field.

- If charge is moved perpendicular to the field lines then no work will be done

• The work done in moving charge +q will store electrostatic potential energy . If the repulsive force between the charges is allowed to act by itself, then the stored electrical potential energy will be converted back to kinetic energy of motion as the particles fly away from each other.

- No work is done on a charge by an electric field when the charge moves along equipotential lines

• Work is done when shifting from one equipotential line to another

Students should be able to recall that electric charge can be positive or negative, define electrical potential difference, and solve problems involving electric potential (Unit 1 Topic 3: Electrical circuits).

- Charges can be positive or negative

• Negative charge is an excess of electrons

• Positive charge is a deficiency of electrons

• Conventional current is the flow of positive charge

- Electrical potential difference is the work done in moving a unit charge between the final and initial positions in an electric field

- Electric potential is the electric potential energy stored per unit charge at any given point

• Electrical potential energy is the energy residing in a charged object and the field at that point
• Electric potential is a measure of the energy per coulomb of a charged object at that point