Make careful observations and record them on your whiteboards. Make careful observations and record them on your whiteboards. Take a few minutes to talk to your neighbors. What is going on? What is causing the meter stick to rotate? Is there a force acting? Explain. Take a few minutes to talk to your neighbors. What is going on? What is causing the meter stick to rotate? Is there a force acting? Explain. What do you think?

Electrostatics

Electrostatics Electrostatics involves electric charges, the forces between them, and their behavior in materials. Electrostatics involves electric charges, the forces between them, and their behavior in materials.

Electric Charges and Forces There are two types of charge: positive charges and negative charges ATTRACTREPEL Like charges repel, opposite charges attract.

Electrons, Protons, & Atoms Helium atom Electrons Protons Atoms are made up of small particles called protons, neutrons, and electrons. Atoms are made up of small particles called protons, neutrons, and electrons. Electrons carry negative (-) charge. Electrons carry negative (-) charge. Loosely bound to atoms and therefore easily transferred from one atom to another. Loosely bound to atoms and therefore easily transferred from one atom to another. Protons carry positive (+) charge. Protons carry positive (+) charge. Tightly locked within the nucleus and therefore not transferred. Tightly locked within the nucleus and therefore not transferred. In an atom, the # of protons = # of electrons (i.e. neutral—no net charge). In an atom, the # of protons = # of electrons (i.e. neutral—no net charge). Objects are usually neutral but can easily acquire or lose electrons to become charged. Objects are usually neutral but can easily acquire or lose electrons to become charged.

Conductors and Insulators Q: What is meant by the term electrical conductor? Q: What is meant by the term electrical conductor? Provide a few examples. Provide a few examples. Q: What is meant by the term electrical insulator? Q: What is meant by the term electrical insulator? Provide a few examples. Provide a few examples. Q: Why do conductors and insulators behave differently? Q: Why do conductors and insulators behave differently? A: Conductors allow electrons to flow freely through them. Silver, copper, aluminum, and other metals A: Electrons do not flow freely though insulators. Plastic, rubber, glass A: Outer electrons in metals are loosely bound to the nucleus and relatively free to move.

Charging by Contact Electrons move easily so an object can become charged by rubbing electrons off the object’s surface. Electrons move easily so an object can become charged by rubbing electrons off the object’s surface. Ex) Brushing your hair with a plastic comb. Ex) Brushing your hair with a plastic comb. Walk across a carpet with plastic- soled shoes. Walk across a carpet with plastic- soled shoes. When rubbing a balloon on your hair, electrons are attracted to the balloon and transfer. When rubbing a balloon on your hair, electrons are attracted to the balloon and transfer. The balloon is left with excess electrons (- charge). The balloon is left with excess electrons (- charge). The hair is left with an equal excess of protons (+ charge). The hair is left with an equal excess of protons (+ charge). Electrons taken off of fur onto rubber rod

Charging by Contact (Conductors) When charging metal, the charge may move through your body into the ground. When charging metal, the charge may move through your body into the ground. The metal and your body are conductors, so the charge moves through them. The metal and your body are conductors, so the charge moves through them. You must hold the conductor with an insulating material, such as rubber gloves, to keep the charge on the metal. You must hold the conductor with an insulating material, such as rubber gloves, to keep the charge on the metal.

Demo: Electroscope The “legs” of an electroscope separate when the electroscope is charged due to the repulsion of like charge on the two legs. Charged plastic rod deposits negative charge (electrons) onto electroscope. “Legs”

Demo: Van de Graff Generator The Human Electroscope Van de Graff deposits large quantities of excess charge on its globe. Van de Graff deposits large quantities of excess charge on its globe. A person with long hair can become a human electroscope. A person with long hair can become a human electroscope.

Conservation of Charge Rod & Fur Neutral Electrons are rubbed off the hairs of a piece of fur, collecting and charging a plastic rod. Electrons are rubbed off the hairs of a piece of fur, collecting and charging a plastic rod. Is the fur also charged? Is the fur also charged? Positive or negative. Positive or negative. Charge cannot be created nor destroyed. Objects become charged by transfer of charges.

Charging by Induction A charged rod is held near a metal sphere. Why do the charges in the metal arrange themselves as shown? The metal sphere is connected to the ground with a conductor. Why did some of the electrons move off the sphere?

Charging by Induction The conductor connecting the sphere to ground is removed. What type of net charge does the sphere now possess? The negatively charged rod is removed. Why do the charges move into the positions shown?

Demo: Charging by Induction Can separate charges by inducing them to opposite sides of a conducting object. Start Neutral Induce +’s to one side Allow –’s to Escape Finish with net + charge

Demo: Electroscope & Induction The legs of the electroscope separate when charged rod brought near the electroscope. Charge induction pushes electrons into the legs. Negatively charged rod repels electrons so they move as far away as possible. “Legs”

Surface Charges Why does a charged balloon stick to the wall? A positive surface charge is induced on the wall by the negatively-charged balloon. Electrons shift within atoms due to attraction or repulsion. The insulator does not have a net charge. The diagram shows the opposite case. Why can a charged comb pick up little pieces of paper?

Demo: Static “Cling” Charged object attracts a neutral insulator by inducing charge polarization in the neutral object. Charged Balloon Neutral Wall Polarization Charged Comb Neutral Paper

Check Yourself What causes a stream of water to be deflected when you bring a charged object next to it?

Lightning Storms Charge separates inside of thunderclouds. The lower part of the cloud is negatively charged. This induces a positive charge on the ground. When the voltage difference is high enough, a lightning bolt can occur.

Make careful observations and record them on your whiteboards. Make careful observations and record them on your whiteboards. Take a few minutes to talk to your neighbors. What is going on? What is causing the meter stick to rotate? Is there a force acting? Is the meter stick a conductor or an insulator? Explain. Take a few minutes to talk to your neighbors. What is going on? What is causing the meter stick to rotate? Is there a force acting? Is the meter stick a conductor or an insulator? Explain. What do you think?