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Science

Electric Fields

Overview

Students explore the invisible forces between charged objects, discovering how electric fields are represented and how Coulomb's law describes the force between charges.

Learning Objective
Students understand the concept of an electric field, how to represent it with field lines, and how electric force depends on charge and distance.

Resources needed

  • A charged balloon (rub on hair or wool)
  • Small pieces of paper or lightweight objects

Lesson stages

0 / 7 done
  1. 1 Demonstrate: rub a balloon on hair. Hold it near small paper pieces — they are attracted.
  2. 2 Ask: is there contact between the balloon and the paper? (No — action at a distance, like gravity and magnetism).
  3. 3 Introduce the electric field: a region of space where a charged particle experiences a force.
  4. 4 Draw electric field lines: they show the direction a positive test charge would move. Lines go from positive to negative charges.
  5. 5 Key rules: field lines never cross; denser lines = stronger field; lines are perpendicular to the surface of a conductor.
  6. 6 Introduce Coulomb's law: the force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them.
  7. 7 Compare to gravitational fields: both follow an inverse square law; both act at a distance; but electric forces can attract or repel, while gravity only attracts.

Tap a step to mark it as done.

Variations

  • Draw the field lines between two like charges and two unlike charges.
  • Calculate the force between two charges using Coulomb's law.
  • Discuss parallel plate capacitors: uniform field between parallel plates — used in capacitors and defibrillators.
More information

Teach: electric field, field line, charge, Coulomb's law, force, attract, repel, inverse square. The field line diagram is the most important visual representation — learn to draw it for point charges and parallel plates.

Focus on the concept of a field and how to represent it with field lines before introducing Coulomb's law quantitatively.

Can students draw correct electric field line diagrams for two point charges and a parallel plate capacitor? Can they state Coulomb's law and predict how force changes when distance is doubled?

A charged balloon attracts paper without touching it — a free demonstration of electric force at a distance. Field line diagrams require only paper and pen.

Students often think electric fields only exist between objects that are touching. The concept of action at a distance — a force transmitted through the field without contact — is one of the most profound ideas in physics.

Electric fields underpin all of electronics, from the transistors in phones to the firing of neurons. Understanding them is fundamental to advanced physics and electrical engineering.