Electric Fields

Orientation

Lesson goal: describe electric fields using field lines, field strength, potential difference, and field-force relationships.

Electric field diagrams are representations of force per unit positive test charge. They are not paths taken by electrons.

Core Content

Electric field strength is force per unit charge:

$$E = \frac{F}{q}$$

For a point charge:

$$E = k\frac{|Q|}{r^2}$$

Potential difference is energy transferred per unit charge:

$$V = \frac{W}{q}$$

Concept Check

1. Electric field strength is:

   • A. force per unit positive charge
   • B. charge per unit time
   • C. energy per kilogram
   • D. resistance per metre

   Answer: A.

2. Electric field lines point in the direction of force on:

   • A. a neutron
   • B. a positive test charge
   • C. an electron only
   • D. a magnetic pole

   Answer: B.

3. Closer field lines usually indicate:

   • A. weaker field
   • B. stronger field
   • C. zero potential
   • D. no force

   Answer: B.

Applied Practice

A charge experiences a force of $0.18\ \text{N}$ in an electric field. The charge is $3.0\times10^{-6}\ \text{C}$. Calculate the electric field strength.

$$E = \frac{F}{q} = \frac{0.18}{3.0\times10^{-6}} = 6.0\times10^4\ \text{N C}^{-1}$$

Final answer: $6.0\times10^4\ \text{N C}^{-1}$.

Deep Practice And Writing

Prompt: explain why field lines around a positive point charge point outward and why their spacing changes with distance.

Tutor Context

Tutor should check whether the student is treating field lines as electron paths. Repair this before adding calculations.

Maintenance Loop

State field definition, field-line direction, and what field-line density represents.

Source Trace

This lesson is materialised from the eduKG custom Year 11 chapter, existing textbook section, roadmap lesson, and Module 4 sequence listed in source_refs.