Mini Physics
Part of Mini EducationSwitch subject
Search

Applications Of Electrostatics

Key idea: O Level electrostatics applications: electrostatic precipitator (core) and applying electrostatic charging to other situations.

  • SEC G3 Physics 2027
On this page

Learning objectives

  • state that there are positive and negative charges and that charge is measured in coulombs
  • state that unlike charges attract and like charges repel
  • Describe an electric field as a region where charge experiences force
  • Recall that the field lines of an isolated point charge give the direction of the force on a positive test charge
  • Draw the directed electric field of an isolated point charge
  • Interpret the electric-field pattern between two isolated point charges
  • Draw the electric-field pattern between two isolated point charges
  • Explain charging by rubbing as electron transfer
  • Describe experiments that charge a conductor by induction
  • Describe potential electrostatic-charging hazards
  • Describe an electrostatic precipitator and transfer the principle

1. Definition

Electrostatic charging can be used to make particles attract or repel so they can be moved or collected.

What you need for this course

You should be able to:

  • describe the use of electrostatic charging in an electrostatic precipitator
  • apply the use of electrostatic charging to new situations

2. Key Ideas

  • Charge particles (or a surface), then use attraction/repulsion so particles move to the right place.
  • In an electric field:
    • a positive charge feels a force along the field direction
    • a negative charge feels a force opposite the field direction
  • In many applications, earthing prevents unwanted charge build-up and improves safety.

3. Detailed Explanations

Electrostatic Precipitator (core)

Electrostatic precipitators remove soot/ash/dust from exhaust gases (e.g. power stations).

  1. The flue gas passes through a region with a strong electric field.
  2. Dust particles become charged as they pass near the charging wires.
  3. The charged dust particles are attracted to oppositely charged (or earthed) collection plates and stick there.
  4. The plates are shaken periodically so the dust falls into a hopper for collection.
Electrostatic precipitatorFlue gas carrying dust enters, particles are charged near wire electrodes, then collected on plates and dropped into a hopper.HopperCollection plateCollection plateCharging wireDirty gas inCleaner gas out
Dust is charged and collected on plates before cleaner gas leaves the chimney.
Exam focus

If you only memorise one application, memorise the electrostatic precipitator steps.

Applying the idea to new situations (examples)

The same idea (charging + attraction/repulsion) is used in many devices.

Photocopier (supplementary transfer example)

A photocopier uses electrostatic charges so toner sticks only where the image is.

Simplified steps:

  1. A drum surface is given charge.
  2. Light discharges selected regions, leaving a charge pattern.
  3. Toner particles with the opposite charge stick to the pattern.
  4. The toner is transferred to paper and heated to fix it.

Spray painting (example)

Paint droplets are charged as they leave the nozzle. The object is earthed (or oppositely charged), so the paint is attracted and spreads out more evenly, reducing paint waste.

Link (safety)

Static sparks can be hazardous near fuels and vapours: Electrostatic Hazards.

4. Common Mistakes

  • Describing the process without mentioning charging and attraction/repulsion.
  • Saying particles are “sucked in” (the force is due to electric fields and opposite charges).
  • Mixing up field direction: field direction is the force direction on a positive test charge.

5. Exam Tips

  • For a precipitator, use a clean 4-step explanation:
    1. particles get charged
    2. particles are attracted to plates
    3. particles stick to plates
    4. plates are cleaned and dust collected
  • Use keywords: charged, attracted, collected, removed.
  • If asked to apply to a new device, write: “charge the particles → use attraction/repulsion to move/collect them”.

6. Worked Examples

Modelled example 1

Electrostatic precipitator (explanation)

Core

Problem

Explain how an electrostatic precipitator reduces particulate air pollution from exhaust gas.
Study the worked solution

  1. Charge the particles

    Method

    Pass dust-laden gas through a strong electric field near charging wires.

    Reason

    The particles must acquire charge before an electric field can direct them effectively.

    Working

    Dust in exhaust → charged dust.

  2. Collect and remove the dust

    Method

    Attract particles to oppositely charged or earthed plates, then shake or clean the plates into a hopper.

    Reason

    Collection takes particles out of the moving gas, and cleaning keeps the plates usable.

    Working

    Charge → attract → collect → remove.

Guided practice 2

Spray painting (why it works)

About 5 min

Problem

Explain why electrostatic spray painting can give a more even coat and reduce paint waste.

Identify the charge arrangement

Object condition

Hints

Hint 1: charge the moving material
Paint droplets leave the nozzle with the same charge sign.
Hint 2: use attraction and mutual repulsion
The object attracts droplets, while like-charged droplets spread apart.
View solution step by step

  1. Attract droplets to the object

    Method

    Charge the droplets and earth or oppositely charge the target.

    Reason

    The electric force draws droplets toward the surface, including around edges.

    Working

    Charged paint → attracted to target.

  2. Explain coverage and waste reduction

    Method

    Use mutual repulsion between like-charged droplets to spread the spray while attraction reduces overspray.

    Reason

    More paint reaches separated parts of the target rather than missing it.

    Working

    Spread + attraction → more even coat, less waste.

Common misconception 3

Applying to a new situation

Find and correct the mistake

Learner response

A factory wants to remove fine dust from workshop air. A student proposes placing a charged plate nearby but never charging the dust. Diagnose and complete the method.

Restore the missing first stage

Required first stage

View solution step by step

  1. Charge the suspended particles

    Method

    Pass the air through a charging region or strong electric field.

    Reason

    A known particle charge makes the force direction controllable.

    Working

    Neutral dust → charged dust.

  2. Collect the particles

    Method

    Attract the charged dust to oppositely charged or earthed plates and remove it from the plates.

    Reason

    Particles that stick to the collector no longer remain in the air stream.

    Working

    Charged dust → plate → collection.

Examiner practice 4

Photocopier (keywords)

4 marks

Supplementary examination question

Explain how a simplified photocopier uses electrostatics to form an image on paper. [4 marks]

Give the four-stage charge-to-fixed-image sequence

View solution step by step

  1. Create the charge image

    2 marks

    Method

    Charge the drum, then use light to discharge selected regions and leave a charge pattern.

    Reason

    The remaining pattern represents where toner should be collected.

    Working

    Uniform drum charge → patterned charge.

  2. Transfer and fix toner

    2 marks

    Method

    Attract oppositely charged toner to the pattern, transfer it to paper and heat-fix it.

    Reason

    Electrostatic force places the toner; heating makes the final image permanent.

    Working

    Pattern → toner → paper → fixed image.

Challenge 5

“New situation” application

Minimal support

Design transfer

A shop wants to reduce airborne dust using a large cleaning unit. Propose an electrostatic method and explain why it works.

Design from the required outcome back to the force sequence

Hints

Hint 1: prepare the particles
Airborne dust needs a net charge.
Hint 2: provide a destination
Use oppositely charged or earthed collector surfaces.
View solution step by step

  1. Create controllable particles

    Method

    Charge dust particles as the air passes through a high-field region.

    Reason

    Charged particles experience a directed electric force.

    Working

    Airborne dust → charged dust.

  2. Remove them from the air

    Method

    Attract the particles to collector plates so they stick, then clean the plates periodically.

    Reason

    Deposited particles no longer leave with the cleaned air stream.

    Working

    Charge → attract → collect → remove.

7. Mind Stretchers

Mind stretcher 1: Charge signExtension

In a precipitator, does it matter whether the dust becomes positively or negatively charged?

Show Answer

No. It only matters that the dust becomes charged, and that the collecting plates have the opposite charge (or are earthed) so the dust is attracted and collected.

Mind stretcher 2: Keeping it safeExtension

Why might earthing be important in devices that use electrostatic charging?

Show Answer

Earthing prevents unwanted charge build-up, reducing the chance of accidental sparks/discharges and helping charge flow away safely.

8. Practice and next step

Rehearse the precipitator as charge → attract → collect → remove and apply that sequence to one unfamiliar device in Static Electricity structured practice. Then complete the topic check to find the next idea to revisit.

Continue with the next resource in this course.

Course and syllabus information
Course
SEC G3 Physics
Edition
SEC G3 Physics 2027