Electrostatics

The Musical genius of Tesla?

Electricity come from the Greek word Elektron Meaning Amber. Electrostatics is the study of electricity at rest.

Electric Force and Charges Protons Positive electric charges Repel positives, but attract negatives Electrons Negative electric charges Repel negatives, but attract positives Neutrons Neutral electric charge

When a balloon is rubbed against your hair and pulled away, your hair clings to it because _________. A.Rubber is very sticky B.The balloon is filled with helium C.The hair and balloon are both positively charged D.The hair is positively charged and the balloon is negatively charged

Rubbing Rubbing your hair with a balloon increases the static charge because ____________. A.Protons are moving from your hair to the balloon. B.The balloon is getting charge from your hair. C.The rubber in the balloon is non- conducting so it allows the electricity to gather D.Hair and rubber are compatible

But what is Charge? A Charge is an imbalance of protons and electrons. Its important to remember that atoms lose or gain electrons not protons. Electric Force and Charges CHECK YOUR ANSWER

A Positive Charge -Has more Protons then electrons Electric Force and Charges CHECK YOUR ANSWER

A Negative Charge -Has more Electrons than Protons Electric Force and Charges CHECK YOUR ANSWER

When thinking of electric force remember The old dating saying that Oposites attract! That’s how charges are, Opposite charges attract and like charges repel each other. Electric Force and Charges CHECK YOUR ANSWER

Conductors and Insulators Conductor: Materials in which one or more of the electrons in the outer shell of its atoms free to wander in the material –Example: Metals such as copper and aluminum Insulators: Materials in which electrons are tightly bound and belong to particular atoms and are not free to wander - Example: Rubber, glass

Superconductors Superconductors: Materials acquire zero resistance (infinite conductivity) to the flow of charge. –Once electric current is established in a superconductor, the electrons flow indefinitely. –With no electrical resistance, current passes through a superconductor without losing energy. –No heat loss occurs when charges flow.

Electric wires are wrapped with rubber or plastic in order to keep you from being electrocuted. This is because the rubber or plastic is a good _____________. A.Insulator B.Conductor C.Transfer point D.Bridge for the electrons

Triboelectricity Charging by friction and contact. Example: Stroking cats fur, combing your hair, rubbing your shoes on a carpet Electrons transfer from one material to another by simply touching. For example, –when a negatively charged rod is placed in contact with a neutral object, some electrons will move to the neutral object.

Charging Due to Friction Glass Acrylic wool

Charging Charging by induction –If you bring a charged object near a conducting surface, electrons are made to move in the surface material, even without physical contact. –Example: The negative charge at the bottom of the cloud induces a positive charge on the buildings below.

Charge Polarization Neutral charges are separated due to a charged object

Charging Induction: Consider two insulated metal spheres A and B. a.They touch each other, so in effect they form a single uncharged conductor. b.When a negatively charged rod is brought near A, electrons in the metal, being free to move, are repelled as far as possible until their mutual repulsion is big enough to balance the influence of the rod. The charge is redistributed. c.If A and B are separated while the rod is still present, each will be equal and oppositely charged.

Charge Polarization If the charged rod is negative, then the positive part of the atom or molecule is tugged in a direction toward the rod, and the negative side of the atom or molecule is pushed in a direction away from the rod.If the charged rod is negative, then the positive part of the atom or molecule is tugged in a direction toward the rod, and the negative side of the atom or molecule is pushed in a direction away from the rod. The positive and negative parts of the atoms and molecules become aligned. They are electrically polarized.The positive and negative parts of the atoms and molecules become aligned. They are electrically polarized.

Charge Polarization Rub an inflated balloon on your hair, and it becomes charged.Rub an inflated balloon on your hair, and it becomes charged. Place the balloon against the wall, and it sticks.Place the balloon against the wall, and it sticks. This is because the charge on the balloon induces an opposite surface charge on the wall.This is because the charge on the balloon induces an opposite surface charge on the wall. Again, closeness wins, for the charge on the balloon is slightly closer to the opposite induced charge than to the charge of same signAgain, closeness wins, for the charge on the balloon is slightly closer to the opposite induced charge than to the charge of same sign

Conservation of charge Charge is never lost it is just transferred to other objects. The total Charge will always remain constant.

What type of charging occurs in a wall when a balloon sticks to the wall? A.Charging by contact B.Charging by friction C.Triboelectric charging D.Polarization

Electric Field Electric field direction Same direction as the force on a positive charge Opposite direction to the force on an electron

The Electric Field The Area around a charged object where it can exert a force on other objects. Positive Plate Negative Plate Neutral Point The field is drawn from + to -

Coulomb’s Law Coulomb’s law Relationship among electrical force, charge, and distance discovered by Charles Coulomb in the 18th century States that for a pair of charged objects that are much smaller than the distance between them, the force between them varies directly, as the product of their charges, and inversely, as the square of the separation distance

Coulomb’s Law Coulomb’s law (continued) If the charges are alike in sign, the force is repelling; if the charges are not alike, the force is attractive. In equation form: k = 9x10 9 Nm 2 /C 2 Unit of charge is coulomb, C Similar to Newton’s law of gravitation for masses Underlies the bonding forces between molecules

According to Coulomb’s law, a pair of particles that are placed twice as far apart will experience forces that are A.half as strong. B.one-quarter as strong. C.twice as strong. D.4 times as strong.

Electric Field

Answer the following question using the picture below. If you placed an proton between plates A and B, in which direction would the proton move? A.Towards plate A B.Towards plate B C.It would not move.

The Superposition Principle When a number of separate charges act on the charge of interest, each exerts an electric force. The electric forces can be calculated separately and added as vectors.

The Superposition Principle Each charge exerts a force on the other. The net force on a charge is the sum of all the forces acting on it by other charges. F net = F 12 – F 23 Remember: if vectors are pointed in the same direction, you add them. But if they are pointed in opposite directions, you subtract!

Practice 1.Three charges are arranged in a line as shown. What is the net force on q 2 ?

Electric Potential Electric potential energy Energy possessed by a charged particle due to its location in an electric field. Work is required to push a charged particle against the electric field of a charged body.

Grounding Since the earth has an massive supply of charges electricity will always want to discharge into the earth.

Lightning Water molecules bumping around in clouds create an enormous charge. These clouds induce a charge on the earth and when enough potential builds up there is a discharge ( lightning)

Electric Shielding Unlike gravitational fields electric fields can be shielded against. When you are fully inside of a conductor the net charge is zero because the charges builds up on the outer surface. This is why if your car gets struck by lighting you will be ok.

Lightning A car being hit by lighting is a great example of electric shielding.

Which of the following reasons explains why you will not be injured if you are inside your car when it is struck by lightning. A.The rubber tires insulate the car. B.The charges applied to the car mutually repel each other and spread around the frame of the car. C.Nonsense! You will be injured when your car is struck by lightning. D.Lightning is repelled by the fuzzy dice hanging from your mirror.

Static Powered Home: the future?

Uses of Static Electricity Spraying a Car Positive Car Negative Spray gun The paint spreads out as each negative drop repels No paint is wasted as the positive car attracts the negative paint

Removing Smoke from Power Station Chimneys Positive Plate Negative Plate Charge up the Smoke No smoke leaves the chimney

Earthing Fuel Tankers Fuel rubbing against the pipe can build up a static charge which could cause an explosion The tanker is joined to the ground with a wire to stop a charge building up