Use electron movement and attraction rules to classify static-charge situations.
Method and worked examples
Electric charge is a property of particles: protons are positive and electrons are negative. In ordinary charging of solid objects, electrons can transfer while protons remain bound in nuclei. An object that gains electrons becomes negatively charged; one that loses electrons becomes positively charged. Charge is conserved: transfer redistributes charge rather than creating it. Like charges repel and unlike charges attract.
A charged object can also attract a neutral object by shifting the neutral object’s charge distribution, a process called polarisation. Attraction alone therefore does not prove two objects have opposite net charges. Conductors allow mobile charges to redistribute readily; insulators restrict this movement. Static charge is an imbalance that can remain on an object until a discharge transfers charge through an available path.
Example 1
A neutral rod gains electrons from a cloth. State the resulting charges.
The rod gains negative charge and becomes negative. The cloth loses electrons and becomes positive; total charge is conserved.
Example 2
A charged balloon attracts neutral paper. Must the paper have a net opposite charge?
No. The balloon can polarise the paper, bringing opposite charge slightly closer. The paper can remain neutral overall while experiencing attraction.
Watch out:Ordinary static charging usually moves electrons. Losing electrons leaves an excess of positive charge.
Charge transfer and static electricity | Year 9 Science | Ascent Arcade