Electricity

Electricity is the flow of electrons… To understand electricity, we first have to review the structure of matter

Atomic Size Atom = Comes from Greek word for “uncuttable” or “indivisible” Smallest unit of an element that still maintains the properties of that element; Building blocks of matter Nucleus Electron Cloud

- Basic Atomic Parts + Sub-atomic Particles Proton Neutron Electron Positively charged (+1) Mass = 1 atomic mass unit (amu) Found in nucleus of atom Neutron Neutrally charged (0) Mass = 1 amu Electron Negatively charged (-1) Mass ≈ 0 amu (is extremely small) Found in energy shells outside nucleus of atom + -

Basic Atomic Structure Nucleus Center of atom 99% of atomic mass in nucleus Where the protons and neutrons are found Electron Cloud (Energy Shells) Regions around nucleus where electrons are found based on how much energy they have Because electrons are not tightly bound in the nucleus, they can move freely N = 3 N = 2 N = 1 Nucleus

THINK! What are the charged parts of the atom? Which part of the atom moves freely around the nucleus?

Neutral v. Charged Because electrons can move freely: When an atom has a balanced number of positive (+) protons and negative (-) electrons, then the object is neutral If more (+) protons, then positively charged If more (-) electrons, then negatively charged Overall, objects that are charged have an unequal number of protons and electrons

THINK! What makes an object positively charged? What makes an object negatively charged? What makes an object neutral?

When electrons move (like when you rub a balloon on your hair or wool), the negative charge moves too! In the balloon case, your hair or wool is left with a positive charge and the balloon now has extra electrons so it has a negative charge Your hair or wool and the balloon “stick together” opposite charges attract positive-negative/ neutral-negative

What if I charge a second balloon by rubbing it against hair or wool…

The second balloon also has a negative charge and it pushes away from the first balloon Same charges repel

Conductors v. Insulators Electrical Conductors are materials that electrons can freely flow through Electrical Conductors distribute electrons throughout an object Ex. Metals, Water, YOU… Insulators are materials that electrons can’t easily move through In insulators electrons get “stuck” in one place Dry air, wood, glass, rubber

THINK! Are electrical conductors/insulators the same or different from heat conductors/insulators? Give an example of a good conductor for electricity and a poor conductor of electricity

Ways of Charging Charging by friction When objects slide past each other One materials gains electrons/ one loses electrons Balloon on head, rubbing your feet on the floor and getting shocked by a doorknob

Charging by conduction (contact) A charged object comes in contact with a neutral object The charged object “gives” its charge to the neutral object Ex. Touching a charged balloon to neutral bits of paper

Charging by induction Bringing a charged object really close to a neutral object BUT not touching it Overall net charge of neutral object stays zero

Exit Ticket: 9-12

9. Which of the following particles has a negative charge? Proton Neutron Electron Atom

10. Which of the following is not a good conductor of electricity? A. Aluminum B. Glass C. Silver D. Copper

11. A conductor differs from an insulator in that a conductor…. Has an excess of protons Has an excess of electrons Can become charged and an insulator cannot None of the above

12. Electrical forces ____. a. can cause objects to only attract each other b. can cause objects to only repel each other c. can cause objects to attract or repel each other d. have no affect on objects