Physics - Electrostatics

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Protons, Neutrons and Electrons

Formation of an atom

• In the centre of an atom there is a nucleus made up of positively charged Protons and neutral Neutrons.
• Negatively charged electrons orbit the outside of an atom in energy levels/shells.

Sub-atomic Particle:            Charge:            Relative Mass:

Proton                                          +                            1

Neutron                                     None                        1

Electron                                        -                             1/1840 (Almost 0)

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Van de Graaf

Van de Graaf

• The pointed electrode produces charge by friction or high voltage.
• Electrons from the electrode are take up to the metal dome by a rubber belt.
• The electrons, due to their negative charge, want to escape and when you touch the metal cover of the Van de Graaf the electrons transfer to your body.
• Your hair sticks on end because it is lightweight. The electrons that have transferred to your body and are in your hair repel as a result of their negative charge, meaning your hair stands on end.
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How do items become charged?

An atom will become charged when it gains or loses an electron. Gaining one or more electrons gives it a negative charge and losing one or more electrons gives it a positive charge.

• When we put a polythene rod (negatively charged) and a perspex rod (positively charged) together they attract due to their opposite charge.
• When we put two polythene rods together they repel and the same happens with two perspex rods as like charges repel.

An insulating material can become electrically charged when rubbed which is a result of gaining or losing electrons. This happens because in an insulating material the electrons are not free to move and so a charge can build up. This does not happen as easily on conductors as the electrons are free to move and so charge does not build up as easily. Metals are an example.

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Uses and dangers of electrostatic charge

Uses

• Spray Painting: The paint has a different charge to the object on which it is sprayed onto. This means that the paint sticks to object as their opposite charges mean they attract.
• Photocopiers: These scan a piece of paper that is to be copied with a positively charged drum. The dark surface of the paper, where the image is, is left positively charged. Then ink, which is negatively charged, is sprayed on and is attracted to the areas with positive charge. This is then rolled across another sheet of paper and copied.

Dangers

• While flying airplanes build up static charges and if, while refuelling, the static is discharged, an explosion could occur.
• Television screens build up static charges and this attracts oppositely charged dust.
• Some clothing builds up a static charge and the wearer could recieve an electric shock.
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