Electricity and Magnetism Part 1: Charge

Inside the Atom… Particle CHARGE MASS Proton Neutron Electron In the middle of each atom is a nucleus. The nucleus contains two subatomic particles: protons and neutrons. Orbiting around the nucleus are smaller subatomic particles called electrons. Particle CHARGE MASS Proton Neutron Electron

Inside the Atom… When the number of protons in an atom equals the number of electrons, the atom itself has no overall charge. It is neutral. Static electricity is the imbalance of positive and negative charges. Atoms that lose electrons have more positive charges (protons) than negative charges (electrons). It is positively charged. An atom that gains electrons has more negative than positive particles. It has a negative charge. When two objects are rubbed together (friction), electrons may be transferred from one object to another.

Electric Fields The area surrounding charged particles/objects within which a force can be exerted on other charged particles/objects. Allows charges to act at a distance. The field can move the charges around an object near it. Charged particles placed in the electric field will be pushed or pulled by the force exerted by the field.

Materials: Some materials transfer electric charge well, others do not. Conductors are materials that allow electrons to flow easily. They readily conduct an electric charge. Ex: Metals (especially copper in wires) and skin Insulators are materials that block the flow of electrons through them. Ex: Plastic, wood, air, rubber, glass

Law of Electric Charges Law 1: Opposites Attract: two items with opposite or different charges (positive and negative) will attract, or pull toward each other. Law 2: Two items with the same charge (both positive or both negative) will repel, or push away from each other. Law 3: Positively charged objects attract neutral objects, and negatively charged objects attract neutral objects. Law of Conservation of Charge: Charge cannot be created or destroyed, only transferred; net electric charge is constant.

Examining Further… If you charge a balloon by rubbing it on your hair, it picks up extra electrons and holds a negative charge. Holding it near a neutral wall will make the negative charges in the wall move away. This is because like charges repel. The result is that there are more positive charges closer to the negative balloon, therefore, attraction. Another Example: When you take off your hat in the winter, it rubs against your hair. Electrons move from your hair to your hat. Now, each of the hairs has the same positive charge. Because objects with like charges repel, the hairs try to get as far away from each other as possible. This is why your hair stands up.

It’s all Give and Take… Electrostatic Series: An electrostatic series is arranged in terms of relative hold that different materials have on their electrons. If you go down the list, these items have a tendency to gain electrons and up the list the tendency to lose electrons.

Sparks If there are enough positive charges on one object and enough negative charges on the surface of another object, the electrons might jump the air gap between them, causing a spark. Ex: Lightning

Charging Objects There are 3 ways an object can become charged. Friction Contact Induction Friction: Static Electricity is produced by rubbing different surfaces together. This causes both surfaces to obtain a different charge. Before rubbing: both objects are neutral. After rubbing, one object loses electrons (Becomes positively charged), the other object gains electrons and becomes negatively charged. Contact Transfer: Contact is common and is the cause of static shocks. Contact transfer occurs when a charged object is brought into contact with a differently charged object. (Includes Neutral Objects) Some or all of the electrons will transfer between the two objects in an attempt to balance the charge.

Charging Objects Static Shocks In the case of static electricity, your body has developed some level of negative charge. When you move your hand toward an uncharged object (especially metals) the excess electrons you have transfer to that object. The movement of the electrons can sometimes be seen as a spark and can occasionally be painful due to the speed at which the electrons transfer.

Charging Objects Charging by Contact: Using a Negative Rod

Charging Objects Charging by Contact: Using a Positive Rod

Charging Objects Induction An electric charge is transferred from one substance to another without direct contact. The induced charge is opposite to that of the charged object producing the charge. Induction Charge Separation: A shift in position of the electrons that produces opposite charge on two sides of a particle.

Charging Objects Charging by Induction: To charge the neutral object, the neutral object must be grounded using a conducting wire. This gives the electrons a place to leave.

Charging Objects Charging by Induction: Using a Positive Rod Using a Negative Rod

Pith Balls and Charge Transference Pith balls, by nature, are usually uncharged to begin with (as are most objects). If a charged object and a pith ball are brought in contact, some of that charge will transfer to the pith ball (either gaining or losing electrons). Once the charged object is removed, the charge remains on the pith ball.

Static Discharge The sudden flow of electric charge between two charged objects, due to a build up of static electricity. Ex: Lightning Movement of clouds and air currents causes a buildup of static electricity in clouds. When e- buildup becomes great enough, a positive charge is induced on Earth. Eventually attraction is so great that the e- travel from the clouds to Earth to neutralize the charge imbalance.

Removing Charge Grounding is the process of removing excess charge on an object by transferring electrons to another object to neutralize the electrical imbalance. Redirects the charge to the ground rather than a building.

Comparison Chart Topic How it’s Charged (Describe how the object becomes charged.) Charge received relative to charge exposed to (Is the charge received the same, or opposite to the object that gave it that charge?) Does the altered charge last? (When the object is isolated, will it retain the charge it was given?) Charging by Friction Charging by Contact Charging by Induction