True or False? A negatively charged object has an excess of electrons. The positive charges move in a metal to balance the movement of free electrons. The amount of charge depends on the mass of an object.

True or False? Uncharged materials cannot be attracted by charged materials. The atoms in the metal plate of an electroscope rearrenge to form eletric dipoles when a charge approaches. The charges collected by the top comb of a Van Der Graaf generator can distribute around the metal dome because this is connected with the comb by metal connections.

Applied Electrostatics

Inkjet printer The ink droplets are charged as they thrust against the nozzle The droplets are deflected as they pass between two electrically charged plates The amount of charge, i.e. the size and direction of the voltage, on the plates keeps changing to drive each droplet to the right place on your paper What charge will the droplets deflected upwardly have? Why? They will be negatively charged, because -ve charges are attracted by the positive plate at the top and repelled by the negative plate at the bottom. A4 paper Fine nozzle Positive plate Negative plate

Photocopier The metal plate is electrically charged and the image to photocopy is projected onto it The lighter parts of your image cause the light to shine on the plate, so that the charge leaks away The charged bits attract black powder which deposits on the paper The paper is heated by the heated rolls, so that the powder sticks on it Negative plate Toner (black powder) Heated rollers

Spray painting The spray nozzle is connected to a positive terminal, so the paint droplets become positively charged This makes them repel each other, so the paint spreads out The object you are painting is connected to the earth (or to a negative terminal) This attracts the paint, giving an even coverage Negative charge Positive nozzle