The electric field is a vector — it has both magnitude and direction at every point.
Electric Force and Potential Difference
A charge placed in an electric field experiences a FORCE:
Positive charge: force in the direction of the field (along field lines).
Negative charge: force opposite to the direction of the field.
The POTENTIAL DIFFERENCE (voltage) drives the movement of charge through an electric field.
NON-CONTACT FORCE:
Electric fields allow charges to exert forces on each other WITHOUT TOUCHING.
This is the same principle as magnetic fields and gravitational fields.
ELECTRIC FIELD STRENGTH:
Defined as the force per unit charge: E = F/q
Stronger field → larger force on a given charge.
BETWEEN PARALLEL PLATES:
Uniform field — force on a charge is constant everywhere between the plates.
Basis of many electronic devices (capacitors, CRT screens, particle accelerators).
Sparks and Electric Discharge
When an ELECTRIC FIELD becomes strong enough, air itself becomes conducting.
SPARKS:
Very strong electric field near a sharp point or charged conductor.
Air molecules ionised — electrons stripped from air atoms.
Ionised air conducts → sudden discharge → spark.
LIGHTNING:
Massive charge builds up in storm clouds.
Electric field between cloud and earth becomes extremely strong.
Air breaks down → conducting channel forms → lightning strikes.
Lightning conductors: pointed metal rods on buildings → provide low-resistance path to earth.
Reduces risk of building being struck or damaged.
STATIC ELECTRICITY LINK:
When a charged object is brought near an earthed conductor:
Electric field between them becomes strong.
A spark (discharge) may occur, transferring charge rapidly.
This is why fuel tankers earth themselves before refuelling — prevents spark igniting fuel.
⚠️ Common Mistake
Electric field lines go from POSITIVE to NEGATIVE — the direction a positive charge would move. Don't confuse with magnetic field lines which go from N to S. A uniform field (between parallel plates) has equal spacing — field strength is the same at all points.
📐 Variables
EElectric field strength (E) is measured in N/C (N/C)
FForce (F) is measured in newtons (N)
qCharge (q) is measured in coulombs (C)
📐 Key Equations
E = F ÷ q
📌 Key Note
Electric field: force per unit charge. Field lines: + to −, closer = stronger. Patterns: single charges radiate; opposite charges arc between them; uniform field between parallel plates. E = F/q. Sparks: air ionised in strong fields. Lightning conductor: provides safe discharge path.
🎯 Matching Activity — Electric Field Patterns
Match each charge configuration to its field pattern. — drag the symbols on the right to match the component names on the left.
Single positive charge
Drop here
Single negative charge
Drop here
Two opposite charges
Drop here
Two parallel plates (+ and −)
Drop here
Field lines arc from positive to negative — strong attractive field between them
Uniform field — parallel equally-spaced lines between the plates
Field lines point INWARD toward the charge from all directions
Field lines radiate OUTWARD in all directions from the charge
🔬 Triple Science Only
Electric fields (physics only) — not in Combined Science.
🎯 Test Yourself
Question 1 of 2
1. In which direction do electric field lines point?
2. Why does a lightning conductor protect a building?
⭐ How Well Do You Understand This Topic?
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