Chapter 7.1 Static Charge

Chapter 7.1Static Charge

Review… • Atom: • Electron (-) • Proton (+) • Neutron (0) • Ions: • Lose electrons = positive ion • Gain electrons = negative ion

Static Charge • Static charge (or static electricity) refers to electric charges that can be collected and held in one place

Static Charge • In any solid material, the nucleus of the atoms is able to vibrate, but can not move. • Only electrons are able to move around. This means that: • All solid materials are charged by the transfer of electrons.

Static Charge • If an electron is taken away from a neutral atom, the atom will then have a positive charge. • If an electron is added to a neutral atom, the atoms will then have a negative charge. • The movement, or transfer, of electrons from one place to another changes the charge on an atom.

Friction and Electron Transfer • Friction occurs when objects rub against each other • Friction causes one object to lose electrons and the other to gain electrons

Friction and Electron Transfer • For example: • Acetate is a type of plastic used in film and overhead transparencies. If acetate is rubbed with paper towel, electrons move from the paper towel onto the acetate. • In A, the paper towel and the acetate are both neutral (equal numbers of + and – charges). • In B, after the paper towel and acetate have been rubbed together, the acetate has more - charges and the paper towel has more + charges.

Insulators and Conductors • Insulators = materials that do not allow charges to move easily • Ex/ glass, rubber, rocks, ceramics, wood • Conductor = materials that allow electrons to travel freely • Ex/ metals, water, people

Insulators • A plastic rod is a good example of an insulator. • If you rubbed only one end of the plastic with a paper towel, only that end of the plastic rod would become charged. The charges can not move through the insulator.

Conductors • Metals allow charges to flow through them. • If you rubbed only one end of a metal rod with the paper towel, the entire metal rod would become charged. • Metals are very good conductors because the atoms in a metal always have at least one electrons that can be easily moved.

Coulombs • Electrical charges are measured in coulombs (C), named after the French physicist Charles Augustin de Coulomb. • It takes 6.25 x 1018 electrons to produce 1 C of charge. • A typical lightning bolt can carry 5 C to 25 C of charge.

Generating Static Charge • There are many examples of using friction in nature to produce static electricity. For example: • The friction between moving air particles in storm clouds produces static charge, which can then travel to Earth as lightning. • A Van de Graaff generator uses friction to generate a charge on a metal dome. A moving belt produces a static charge at the base of the generator, which then collects on the dome.

Applications of Static Charge • Although static electricity is often unwanted (hence the reason most of us use dryer sheets in the laundry), it can be useful. For example: • Static electricity makes Saran wrap “sticky”. • Devices in chimneys collect particles that would normally flow out into the air. • When painting cars, the paint is given an electrical charge so that it sticks to the metal of the car and nowhere else.

Dangers of Static Charge • Sometimes static charge can be dangerous. Trucks that deliver fuel must have a special cable that allows any static charge to flow into the Earth. This prevents any sparks that could cause the fuel to explode. Allowing charge to flow into the Earth is called grounding. The Earth is so big that it can accept a lot of charge without becoming charged itself. • To protect a building from lightning, a lightning rod is placed on top of the building. If lightning occurs near the building, the charge will pass through the rod to the ground, rather than into the building.

Chapter 7.1 Static Charge