Static Charge | Physics

📖 In-Depth Theory

Building Up Static Charge

STATIC ELECTRICITY arises when electric charge builds up on an insulating material.

HOW STATIC CHARGE BUILDS UP:

When two insulating materials are RUBBED together, electrons transfer from one to the other.

Material gaining electrons → becomes NEGATIVELY charged.

Material losing electrons → becomes POSITIVELY charged.

CHARGE IS CONSERVED: total charge before = total charge after. The charges are equal and opposite.

EXAMPLES:

Rubbing a plastic rod with a cloth: rod becomes negatively charged, cloth becomes positively charged.

Walking on carpet: body builds up charge (electrons transfer to feet or from carpet).

Nylon clothing rubbed against skin.

ONLY ELECTRONS MOVE — protons are fixed in the nucleus. Positive charge is created by REMOVING electrons, not by adding protons.

INSULATORS vs CONDUCTORS:

Insulators: charge stays where it is built up — cannot flow away.

Conductors: charge spreads across the surface immediately — cannot build up static.

Forces Between Charges

LIKE CHARGES REPEL — two positive charges or two negative charges push each other apart.

OPPOSITE CHARGES ATTRACT — positive and negative charges pull each other together.

This is a NON-CONTACT FORCE — charges exert forces across empty space.

DEMONSTRATIONS:

Charged balloon sticks to a wall — the charged balloon induces an opposite charge on the wall surface.

Two charged rods of same material repel each other.

Hair standing up after rubbing — all hairs gain the same charge and repel each other.

INDUCTION:

A charged object brought near a neutral conductor causes charge SEPARATION (induction).

Free electrons in conductor move towards or away from the charged object.

Nearest end becomes opposite charge to the object → attraction.

ELECTROSTATIC HAZARDS:

Fuel tankers: static builds up from fuel flowing through pipes → spark → fire/explosion risk.

Electronic components: sensitive to electrostatic discharge (ESD) — wear antistatic wristbands.

Lightning: massive electrostatic discharge between cloud and earth.

Applications of Static Electricity

INKJET PRINTERS:

Tiny ink droplets given different charges → deflected by charged plates → precise positioning.

Computer controls charge on each droplet → forms text and images.

LASER PRINTERS / PHOTOCOPIERS:

Drum given static charge.

Laser removes charge from non-printing areas.

Toner (charged powder) sticks to charged areas → transferred to paper → heated to fuse.

ELECTROSTATIC PRECIPITATORS (smoke filters):

Electrodes create strong electric field in chimney.

Soot particles gain charge → attracted to oppositely charged plates → fall into collection bin.

Reduces particulate pollution from power stations and factories.

SPRAY PAINTING:

Spray gun charges paint droplets.

Object to be painted is given opposite charge.

Paint attracted to surface evenly — even coverage, less waste.

Used in car manufacturing.

DEFIBRILLATORS:

Deliver controlled electric shock to restart heart.

Capacitors store charge then discharge through patient's chest.

⚠️ Common Mistake

Only ELECTRONS move when static charge builds up — positive charges do not move. Rubbing makes one object negative (gains electrons) and one positive (loses electrons). Like charges repel, opposite charges attract — the same rule as for magnets but remember that electrical charges and magnetic poles are completely different things.

📌 Key Note

Static: electrons transfer when insulators rubbed → one negative, one positive. Like charges repel; opposite attract. Conductors can't hold static (charge flows). Applications: inkjet printers, photocopiers, precipitators, spray painting. Hazards: fuel tankers, ESD. Induction: charged object causes charge separation in neutral conductor.

🎯 Matching Activity — Static Charge

Match each scenario to the correct electrostatic explanation. — drag the symbols on the right to match the component names on the left.

Negative charge on rod

Drop here

Positive charge on cloth

Drop here

Balloon sticks to wall

Drop here

Hair standing up after rubbing

Drop here

Loses electrons to the rod — left with net positive charge

Balloon induces opposite charge on wall surface — opposite charges attract

Gains electrons when rubbed with cloth — electrons transferred to rod

All hairs gain same charge — like charges repel, hairs push apart

🔬 Triple Science Only

Static charge (physics only) — not in Combined Science.

🎯 Test Yourself

Question 1 of 2

1. A plastic rod is rubbed with a woollen cloth and becomes negatively charged. What has happened?

2. Why are electrostatic precipitators used in power station chimneys?

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⚡ Static Charge

Building Up Static Charge

Forces Between Charges

Applications of Static Electricity

Mr. Badmus AI