In this post, let’s talk about the use of electrostatic charging in a photocopier. This is in the O Level Physics syllabus, tested under the topic of static electricity.
Below is the snapshot from the O Level Physics syllabus:
Electrostatic Charging in a photocopier
When you want to make a copy on a photocopier, you put the piece of paper which you want to make a copy of (we call this the master copy) on a glass piece. We then press a button, and a copy of the master is printed out.
This photocopier actually makes use of the principal of electrostatic.
When the master is placed on a sheet of glass. When you press the button to make a copy, a beam of light shines on the master copy and produce an onto a positively charged drum. This drum is coated with selenium. Selenium conducts electricity when illuminated, and is an insulator of electricity (when not illuminated). The bright areas of the image on the drum will lose their charge. The coloured areas remain positively charge.
The photocopier contains a black powder or toner that is negatively charged. This negatively charge powder is then attracted to the positively charged part of the drum, since unlike charges attract. The portion of the drum that is neutral will not have black ink attracted to it. The drum rolls against a piece of paper, and a copy of the master copy is made on the paper.
Sample O Level Physics Questions involving Application of Electrostatic
Let’s look at a typical question from O Level Physics involving application of electrostatic.
Question on electrostatic (answers in blue)
The figure below shows an application of electrostatic charges, known as electrostatic coating. A nozzle produces paint droplets, all of which are given a positive charge. The metal panel is given a negative charge.
(a) Explain why the paint droplets spread out as they leave the nozzle?
Answer: The paint droplets repel each other as they have the same charge.
(b) Explain why this method of painting reduces the amount of paint lost.
Opposite charge attract. The paint droplets are attracted to the metal panel, reducing the amount of paint loss.
(c) It is suggested that the metal panel can be of neutral charge as the positively charged paint droplets would be attracted to neutral objects too. Explain why his suggestion is not feasible in this context?
When the positively charged paint droplets are deposited on the metal panel, the metal panel will become positively charged. Since like charges repel, no more paint will be deposited on the metal panel.
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