Dangers and Uses of Static Charge

Static charge can be both useful and dangerous. The key factor is whether the discharge is controlled.

Useful applications

Electrostatic paint spraying:

• Paint droplets are given the same charge, so they repel each other and spread out evenly.
• The object to be painted is earthed (or oppositely charged), so the paint is attracted to it.
• Less paint is wasted; even coverage, including around curves.

Electrostatic precipitators (removing pollution):

• Smoke particles pass through charged grids.
• The particles gain a charge and are attracted to oppositely charged collecting plates.
• Clean air exits; collected particles are removed periodically.

Photocopiers and laser printers:

• A charged drum attracts toner powder to specific areas.
• The pattern is transferred to paper and heated to fix it.

Dangers

Sparks near flammable substances:

• Fuel flowing through pipes can build up static charge.
• A spark could ignite fuel vapour, causing an explosion.
• Solution: earth (ground) metal containers and pipes; use conducting hoses.

Lightning:

• Charge separates in clouds (friction between ice particles).
• When the charge is large enough, a spark (lightning bolt) discharges to the ground or another cloud.
• Lightning conductors provide a safe path to earth.

Electric shocks:

• Touching a charged object can cause a sudden discharge through the body.
• Usually harmless but startling; can be dangerous near sensitive equipment.

Common errors and how to correct them

• Saying the object in paint spraying is charged the same as the paint. The object has the opposite charge (or is earthed) so it attracts the paint.
• Forgetting that earthing is the key safety measure for static charge dangers.

How to apply this in an exam

For uses, explain the charging mechanism and why it achieves the desired result. For dangers, explain how charge builds up and how earthing prevents sparks.