Electrostatics

Do Now In your notes: Draw an atom of either Helium, Lithium, or Carbon Label all the parts of your atom. Feel free to use your phone for some research!

The first scientist to study these phenomena was Benjamin Franklin (1706-1790). Franklin called this property gained by rubbed objects electric charge, and called the phenomenon charging by friction. He spent a large amount of his fortune purchasing exotic materials, such as silk, to determine several overarching patterns.

amber Ben Franklin chose to call an amber rod negatively charged after it was rubbed with fur, and called the fur positively charged. fur This was an arbitrary choice, but formed the basis for the naming convention still used today.

If we assume the Tube becomes negative when rubbed with fur, figure out the charge of all the objects from your lab: + or - Foam Tube Fur

Review of Charge Charge (Q or q): Fundamental unit of Electricity Two Types: Positive and Negative Source of Charge: Protons (+), Electrons (-)

Charges Exert Forces on Each Other Like Charges Repel and Opposite Charges Attract *The closer the charges are, the stronger the force

How do Atoms Become Charged? To become negative, an atom can gain an electron To become positive, an atom can lose an electron

How do Atoms Become Charged? Protons are never transferred since they are locked in the nucleus! The only way for objects to become charged is by transferring electrons.

Types of Materials Conductors Insulators outer electrons free to move throughout material Ex: metals Insulators electrons tightly bound to atoms Ex: plastic, rubber, glass

Methods of Charging What has happened to cause the dog’s hairs to behave the way they do after the dog is rubbed with the blanket?

Methods of Charging Charging by Friction – 2 uncharged materials are rubbed against each other electrons transfer from one material to another due to atoms of one material “pulling” electrons more strongly than the other Objects end with OPPOSITE CHARGE (equal amounts)

Methods of Charging Charging by Contact – touch a charged object to uncharged object Electrons move one object to another Objects end with same charge

If you touch the objects with the charged rod, what will happen? Insulator Conductor foam Electrons from the rod are deposited on the objects. On an insulator the electrons stay put On an conductor the electrons repel and spread out to the very edge

If you touch the objects with the charged rod, what will happen? Metal Sphere foam Electrons from the objects are attracted to the foam (making the rod less +) Electrons from the entire sphere are attracted to the foam, leaving whole sphere + In an insulator, only nearby atoms loose electrons and become +

Charging by Polarization Charging by Polarization– bring a charged object NEAR a neutral object Separates the charges in the neutral object by moving the electrons Object still has a net charge of 0

What if you bring the charged foam near an insulator ? The charged object repels/attracts the electron clouds – either bringing them closer or farther. This causes the attraction to be stronger than the repulsion! Figure 14.2

What if you bring the charged foam near water? Water molecules are already polarized! So they turn to put the H+ side toward the negative object! foam Figure 14.2

Grounding Grounding – Connecting an object to the ground (the Earth) to avoid build up of charge Any excess electrons will flow into the ground Any lack of electrons will be replaced by electrons from the ground.

Charging by Induction A way to charge a neutral conductor using BOTH polarization and grounding

Charging by Induction (Conductors) Charged object brought near an uncharged conductor Separation of charge develops Negative Charge leaves the conductor by grounding the conductor Ground is removed and the conductor now has a net positive charge

Charging Two Spheres By Induction: Bring a Charged object near the spheres Separate the spheres while the charged object is still nearby. The spheres end with opposite charge

Polarization Grounding Induction Charging By Friction Charging By Contact Induction

Van de Graaff Generator Electrons transferred by belt to the metal conducting sphere where they spread out

Lightning The negative side of a raincloud can induce a positive charge on the ground Lightning occurs when so much charge builds up, that air is turned into a conductor Lightning: The huge flow of electricity excites atoms causing them to emit huge amounts of light Thunder: The electricity rapidly heats the air, making it expand quickly, sending out a shock wave of sound

Lightning

Lightning Rods Invented by Benjamin Franklin