Uses of static electricity
4 marks · NormalIn a factory, car doors are painted using electrostatic spraying.
Describe how charges are arranged in the spray gun and on the car door during the process.
Explain, using physics ideas, how electrostatic spraying improves the efficiency of painting compared to uncharged methods.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) The paint droplets leaving the spray gun are given one type of electric charge (e.g. positive); the car door has the opposite charge (e.g. negative).
(b) Charged droplets are attracted to the oppositely charged door, causing more paint to reach the surface and less to be wasted. The repulsion between droplets helps the paint to spread evenly, increasing efficiency and reducing waste.
Common mistakes: Not mentioning the charges of the gun and the door
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States spray gun gives charge to droplets.
B2 (a) · 1 mark · States car door has opposite charge to droplets.
B3 (b) · 1 mark · Explains attraction to oppositely charged object improves coating/efficiency.
B4 (b) · 1 mark · Mentions repulsion of droplets helps them spread evenly over surface.
Worked solution
a) Droplets from the spray gun have a charge (for example, positive), and the car door is given the opposite charge (negative).
b) The electrical attraction between opposite charges pulls more paint onto the door, helping it stick to all surfaces including corners. Repulsion between like charged droplets helps spread them more evenly, making the process more efficient and reducing paint wasted as overspray.