Uses of static electricity
4 marks · NormalA factory uses an electrostatic method to spray powder onto plastic objects.
State what charge should be given to the powder and to the plastic objects to ensure the powder is attracted to the objects.
Explain how electrostatic forces help the powder to coat all parts of the plastic objects, even on surfaces that are hard to reach.
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(a) Powder should have an opposite charge to the objects (e.g. powder negative, objects positive, or vice versa)
(b) Electrostatic attraction causes the powder to be drawn to all surfaces, including corners and hidden areas, because opposite charges attract and the like charges on the powder cause the particles to repel, creating an even coating.
Common mistakes: Saying the same charge for both powder and object; Forgetting that the powder and object MUST have opposite charges
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Marking points
B1 (a) · 1 mark · Powder and plastic object must have opposite charges.
M1 (b) · 1 mark · States that electrostatic attraction causes the powder to be attracted to the object.
A1 (b) · 1 mark · Describes that like charges on powder particles cause repulsion so they spread evenly.
A2 (b) · 1 mark · Explains that this allows all areas, including hard-to-reach surfaces, to be coated.
Worked solution
a) To ensure powder is attracted, the powder and objects must have opposite charges (e.g. powder negative, objects positive).
b) The oppositely charged powder particles are attracted to the plastic objects due to electrostatic attraction. Since the particles on the powder repel each other, they spread out and form a thin, even coating. Because the attraction is not just direct line of sight, powder is pulled into corners and hard-to-reach surfaces, ensuring all areas are covered.