Bellringer How do you find the area of

Bellringer • How do you find the area of a triangle? • This was the most missed question on the test… DO STOP WORK

Objectives • Investigate the majesty of electricity so you can soon control lightning like Zeus. • Also so you can solve Regents questions…

Updates • Midterm next week (Feb 3 rd) • Tests • Create your own labs • Power Labs

Notes • Remember that the second marking period ends this Friday • So if you have any missing labs, or homework assignments you need to turn them in ASAP otherwise they will be zeros forever.

Congratulations! • You’ve made it through mechanics!! • Now onto the cool stuff!

Electrostatics

Electrostatics • Electrostatics is the study of electric charges that can be collected and held in one place. • Electrostatics is the study of static electricity!

Electrostatics • The effects of electrostatics are observable over a vast range of scales.

What is an “Electrical” charge? • The electrical charge of an object refers to the amount of extra electrons it does or doesn’t have. • There are two types of electrical charges. ▫ Positive (+) ▫ Negative(-) • If an object does not have an electrical charge it is said to be neutral, or have zero charge.

Electric Charges • Atoms only care about the electrons in their filled shells. • Atoms can lose or gain extra electrons causing the atom to no longer be neutral ▫ Extra electrons = negative charge ▫ Deficit of electrons = positive • Protons don’t move!!!!

Where do electric charges come from? • Electrical charges come from any kind of transfer of electrons. • Balloon Demo ▫ How does the balloon get its charge? ▫ What can it do with a charge?

Can electric charges produce a force? • Based on the balloon activity what do you think? • Yes they can! It is called the “Electrostatic force” • What variables do you think effect it?

The Electrostatic Force •

The Electrostatic Force • Does this force always attract like gravity? • How could we find out? • Electroscope/Wimshurst Demo

Bellringer 3 QUESTIONS!!!!! 1. Opposite charges ______. 2. Like charges _____. 3. Can protons flow like electrons? DO STOP WORK

Objectives • Continue to investigate the wonders of electricity • Solve some problems with your new found knowledge

The Electrostatic Force • The electrostatic force can be both attractive and repulsive. • Like charges repel • Opposite charges attract

Electrostatic Vocab • Conductor: A material that allows charges to move about easily ▫ Usually metals • Insulator: A material through which a charge will not move easily. ▫ Usually plastics

Wimshurst Machine Demos • Wimshurst Machine Demos ▫ Sparks, plates, bowl, ring • Defibulators ▫ About 1, 000 volts sent across your heart muscle

Where do sparks come from? • Sparks are a continuous discharge of electrons. • Is air a conductor or insulator? ▫ Air is generally considered an insulator, but under certain conditions it can become a conductor (sparks fly)

Where do the electrons go on a charged object? • Electrons are all negatively charged so they repel each other. • So when an object is holding a charge it is evenly distributed throughout it

Van Der Graaf Generator • Demos

Bellringer 3 QUESTIONS!!!!! 1. Opposite charges ______. 2. Like charges _____. 3. Can protons flow like electrons? DO STOP WORK

Objectives • Continue to investigate the wonders of electricity • Solve some problems with your new found knowledge

Reminders • 80 and below = SLC • Physics Club today after school • Your Midterm is a week from today. STUDY UP!

Conservation of Charge • The charge of a system must be conserved • A system can only gain or lose electrons by interacting with another system.

Ways to charge 1. Charging by Conduction: Charging a neutral object by touching that object with a charged object. 2. Charging by Induction: Charging a neutral object by bringing a charged object near it.

Charging By Conduction • Many of the demos we’ve done already. • Electroscope

Charging by Induction • Electroscope Demo

Induction Charging People Demo

Conductive vs. Inductive • Conductive ▫ Needs contact ▫ The object that gets charged is the same charge as the charger • Inductive ▫ No contact ▫ The object that gets charged is the opposite charge as the charger

Checkpoint 1. What are two differences between charging by conduction vs induction?

Example • If a positively charged rod conductively charges an electroscope. What charge will the electroscope have? • Positive

Example • What charge will the leafs of the electroscope have after it is charged inductively? • Positive

The Coulomb • What is a “Coulomb”? • It is the standard unit for electrical charge (C) • Named after Charles-Augustin de Coulomb, a French physicist who developed Coulomb’s Law

The Coulomb • One Coulomb is 6. 25 x 10^18 elementary charges • One elementary charge is the charge of one proton, or one electron ▫ One elementary charge (e) is 1. 60 x 10^-19 C

The Coulomb • Static electric shocks from doorknobs, socks, etc. are typically only a few microcoulombs • Lightning bolts are around 15 C • The amount of charge that travels through a AA battery is about 5, 000 C

Coulomb Questions • • • Is it possible to have a charge of 2. 8 x 10^-19 C? Nope What about 3. 2 x 10^-19 C? Yup How much charge is gained when something gains 4 electrons? • -6. 4 x 10^-19 C

The Elementary Charge • The elementary charge is the charge of a single electron • It was discovered by American physicist Robert Andrews Millikan in his famous Millikan oil drop experiment in 1909. ▫ His measurement has been updated

Millikan Oil Drop • He sprayed drops of oil between to differently charged plates and balanced the downward gravitational force with the upward electrical force.

Coulomb’s Law •

Example •

You try •

Bellringer • What is the electrostatic force between an electron and a proton that are 5. 26 x 10^-11 m apart? • -8. 32 x 10^-8 N DO STOP WORK

Objectives • Solve some problems with your new found knowledge of the universe • Learn what force field is and how to use it

Updates • Below an 80 = SLC • Only a few days left in this quarter ▫ #checkyogrades • Midterm next Tuesday ▫ All Regents Questions

Example Problem • Page 559

Practice • Page 560 of the textbook, questions: 9 -14

Answers 9. 1. 6 x 10^4 N attractive 10. 3. 0 x 10^-6 C 11. The force diagram is reflected about the y-axis with respect to the diagram shown in Example Problem 1. Magnitudes of all forces remain the same. The direction changes 42 degrees above the negative x-axis, or 138 degrees counterclockwise from the positive x-axis

Answers 12. The electrostatic force between the two charges decreases by a factor of 9 (3 squared) 13. 0. 068 N towards the right 14. 3. 1 N toward the right

Simulation • https: //phet. colorado. edu/en/simulation/balloo ns

Homework • Page 561 15 -23 ▫ Will be collected. ▫ You may need to read the previous chapter to answer the questions.

Bellringer – Take out your HW • How many more electrons are there than protons in a -1. 5 Coulomb charge? • 9. 38 x 10^18 electrons DO STOP WORK

Objectives • Go over homework • Learn what force field is and how to use it

Updates • Below an 80 = SLC • Only a two days left in this quarter ▫ #checkyogrades • Midterm next Tuesday ▫ All Regents Questions

Homework • Page 561 15 -23 ▫ Will be collected. ▫ You may need to read the previous chapter to answer the questions.

Simulation • https: //phet. colorado. edu/en/simulation/balloo ns

Force Fields • How would you define a “force field”? • Have you ever been in a force field before? • Can gravity be a force field?

Gravitational Field • Draw a few vectors around the Earth to show which way Earth’s Gravitational Field pulls at an given point.

Electric Field • Just like the gravitational force, the electrostatic force produces a force field too. • An Electric Field is a property of the space around a charged object that exerts forces on other charged objects.

Electric Field • Since the electrostatic force can both attract and repel the field lines are not always pointed in

Electric Field • Those vectors are called “Electric Field Lines” • An “Electric Field Line” indicates the direction of the force due to the electric field on a positive test charge • They started using positive “test” charges before they realized that only electrons (negative) move.

Checkpoint 1. What is an “electric field”? 2. What is an “electric field line”? 3. Why do they use positive test charges if protons don’t flow?

• Try to visualize what you think the electric field lines will look like between a positive and a negative point charge. • Note: You can never cross electric field lines

• What about the electric field lines between two positive charges?

• What about the electric field lines between two negative charges?

This is like the two oppositely charged plates with the pieces of foil demo.

Electric Field Lines • Electric Field Simulation ▫ https: //phet. colorado. edu/en/simulation/charges -and-fields • Electric Field Demonstration ▫ http: //www. youtube. com/watch? v=7 vnm. L 853784

Bellringer – Take out your HW • How many more electrons are there than protons in a -1. 5 Coulomb charge? • 9. 38 x 10^18 electrons DO STOP WORK

Objectives • Go over homework • Learn what force field is and how to use it

Updates • Below an 80 = SLC • Only a two days left in this quarter ▫ #checkyogrades • Midterm next Tuesday ▫ All Regents Questions

Electric Field Strength • The strength of every electric field is not the same. Just like every gravitational field is not the same. • It depends on the electrostatic force and the charge of the object in the field.

Electric Field Strength •

Example • Suppose that you are measuring an electric field using a positive test charge of 3. 0 x 10^-6 C. This test charge experiences a force of 0. 12 N. What is the magnitude of the electric field strength at the location of the test charge?

Example Solution •

You Try •

Bellringer • Draw at least 6 electric field lines between these three charges. DO STOP WORK

Objectives • Solve some problems with your new found knowledge of the universe • Learn what force field is and how to use it

Reminder • All missing labs and homework assignments are due tomorrow • If you don’t hand them in by then they will be zeros forever ▫ *Zeros bring your average down big time.

Example •

Practice • Page 572 -573, numbers 1, 2, 4, 5, 6, 8, 9, 10

Answers 1. 2. 4. 5. 6. 40 N/C 3. 0 x 10^6 N/C 3. 0 x 10^5 N/C , 0. 65 N , 3. 0 x 10^-6 C 8. 1 x 10^-6 N south 1. 6 x 10^4 N/C toward q

Answers 8. 2. 6 x 10^4 N/C 9. 6. 5 x 10^3 N/C 10. 2. 5 x 10^4 N/C east

Homework • Page 590 Numbers 50, 51, 53 a, 53 b, 53 d, 54, 55, 56

Bellringer • DO STOP WORK

Objectives • Go over midterm

Updates • SLC today! 79 or below on the Energy Test • Midterm… ▫ 63. 8% average ▫ 7. 1 points behind last year

Midterm Analysis • Must be completed by everyone. • Corrections ▫ Show all work for every question you lost any credit on. • Due Friday the 13 th of February 2015

Work done on a charge •

Electric Potential Difference • Small difference… • The work done on a charge is expressed as work done per unit charge and it is called the “electric potential difference” • Often just called the potential difference

Electric Potential Difference • Electric potential difference is the work needed to move a positive test charge from one point to another, divided by the magnitude of the test charge. • You can also think of electric potential difference as the change in electric potential energy per unit charge.

Electric Potential Difference •

Positive Electric Potential Difference A B PE Work PE A positive force is required to move a positive charge a distance away from a negative charge, so positive work is done.

Negative Electric Potential Difference A B PE Work PE A negative force is required to move a positive charge a distance toward a negative charge, so negative work is done.

Checkpoint 1. What are the units of potential difference? 2. Do you do negative or positive work to separate a positive and negative charge?

Example •

You Try •

Parallel Plates – Uniform Electric Field

Electric Potential Difference in a Uniform Electric Field •

Example • What is the electric field between two parallel plates that have a potential difference of 200 volts and are 0. 20 m apart? • V=Ed • 200 V=E(0. 20 m) • E=1, 000 N/C

Practice • The electric field intensity between two large charged parallel metal plates in 6, 000 N/C. The plates are 0. 05 m apart. What is the potential difference between them? • 300 V • A voltmeter reads 400 V across two charged, parallel plates that are 0. 020 m apart. What is the magnitude of the electric field between them? • 20, 000 N/C

Homework • Electrostatics multiple choice practice homework numbers 1 through 25

Bellringer • DO STOP WORK

Objectives • Scantrons • Finish notes on electrostatics • Practice everything we’ve learned about electrostatics so far

Bellringer • Draw the electric field lines for the charges (you have 2 mins) • Take out your HW

Objectives • Review last night’s homework • Review the midterm and a way to get points back…

Electronvolt • An electronvolt is a unit of energy commonly used in electrostatics (unit e. V) • One electronvolt is 1. 6 x 10^-19 joules • It is the amount of energy gained or lost by the charge of a single electron moved across an electric potential difference of one volt.

Electronvolt: the super unit! Measurement Unit Energy e. V Mass e. V/c^2 Momentum e. V/c Temperature e. V/k(b) Time h(bar)/e. V Distance h(bar)c/e. V

Practice •

You Try •

Shortcut • Just multiple the number of electrons by the voltage! ▫ (Electronvolt) • How much energy is gained by moving 3 electrons across 12 volts? • 36 e. V

Why use electronvolts? • When you are just working with a single electron, or a beam of electrons, it makes math way easier by using e. Vs. • This way the voltage and the energy are the same number!

Electron Gun http: //www. mrwaynesclass. com/electro/reading/ index 06. html

Electron Beam • Demo • Old TV’s

Particle Accelerator • http: //www. youtube. com/watch? v=b 5 Q 5 r. Ff-a. ZI

Homework • Electrostatics multiple choice practice homework numbers 1 through 25

Bellringer • Draw the electric field lines for the charges (you have 2 mins) • Take out your HW

Objectives • Review last night’s homework • Review the midterm and a way to get points back…

Updates • Skipping SLC • Midterm analysis due Friday the 13 th • Electrostatic test next week (Wednesday? )

Homework • https: //www. youtube. com/watch? v=Js. VZwc 1 d. Oo • Any questions?

Classwork • Questions 26 -43 (15 mins) • Go over Midterm Part 2 • Homework (Finish Electrostatics MC Questions)

Bellringer • What is the energy (in electronvolts) gained or lost when one electron is moved across a 1 volt potential difference? • 1 e. V DO STOP WORK

Objectives • Review last weekend’s homework • Practice part twos for the Electrostatics Test

Updates • SLC anytime this week • Test on tomorrow or Thursday • Midterm analysis due Friday

Homework • Homework Questions • https: //www. youtube. com/watch? v=Js. VZwc 1 d. Oo • Practice Problem

Electrostatics Test • Wednesday or Thursday? • 25 multiple choice questions • 6 written response • See me if you have questions

Homework • Any questions? • Tonight’s Homework: 1. Study for your electrostatics test 2. Work on/complete your test corrections

Video • http: //www. youtube. com/watch? v=Vh. WQr 1 LYXY

Midterm • Let’s go over it…

Bellringer • Is it dangerous to ride on a train that is traveling through a lightning storm? • Well it depends on the conductor!

Objective • Review for tomorrow’s test

Electrostatics Test • 25 multiple choice • 14 long answer parts (6 questions)

Extra Credit Assignment • Go to http: //www. nsf. gov/news/special_reports/olym pics/ and watch one of the videos • Write a summary of a the video or write a summary of physics in a different winter Olympic sport

Midterm Corrections • Remember they are due this Thursday before I leave the building.

Sample Part Two Questions