Electrical charges and forces

Electrostatics Electrical charges can be collected and held in one place. When this occurs, this is referred to as static electricity as the word static means to remain in place. Electrical charges can be either positive (loss of electrons) or negative (gain of electrons). The word electricity has to do with the flow of electrons. Like charges repel Opposite charges attract + - + - + -

Charged objects A conductor is an object that allows charges to through it freely. This is due to the fact that most conductors are metals that have mostly empty outer electron levels. As this is the case, metals can gain and lose electrons very easily. An insulator is an object that does not easily allow charges to flow. Rubber, plastics, glass, wood and air are all insulators.

Electrical force Electricity can be transferred in three ways Charging by contact – the transfer of charge happens due to an imbalance of charge on contact. ex. Touching a door knob after walking across carpet

Electrical force Charging by friction – the transfer of charge between two objects by rubbing them together. ex. Rub a balloon against your hair. The balloon will take on a negative charge as your hair gives away electrons.

Electrical force Charging by induction – an object with segregated charges causes a nearby neutral object to separate its charges. When the objects are close enough together (but not in contact), a static discharge occurs. ex. lightning

So…how does electricity have force? Charles Coulomb (coo-lomb) conducted an experiment to determine the force between two small conducting spheres. He found that the electrical force between the spheres (attraction or repulsion) was depended upon distance. More specifically the force was approximately equal to the inverse square of the distance. F  1/d2

Coulomb’s law Through more experimentation Coulomb was able to determine the magnitude of force between two charges (Coulomb’s Law) FE = k (q1q2/d2) F is the force in Newtons k is a constant, 9.0 x 109 N.m2/C2 q is the charge of a particle (1 or 2) which is measured in Coulombs d is distance which is squared

So what is a Coulomb???? A Coulomb is the SI unit of charge. It is equal to 6.25 x 1018 electrons or protons. A Coulomb is a big unit. About 10 Coulombs is equal to the charge of a large lightning bolt. We will be dealing with very small units in Coulombs. One electron has a charge equal to about 1.6 x 10-19 C. Like charges cause a repulsion force. Opposite charges cause an attractive force.

THE Van de Graaff generator The Van de Graaff generator is a fun device to show how static charge is built up until there is enough electric force to create and inductive discharge. Fortunately, the amperage of such a discharge is relatively low but it can still give you a nice zap! The kinetic energy of the moving belt (D) causes a build up of static electricity on a conducting wire brush that is just beyond contact with the belt. Static charges build up on the brush and are transferred to the dome. If person or object is close enough to receive the charge …..ZAP! TIME TO PLAY!!!!!!!!