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 chargePositive nozzle