December 11 2017 Describe how charged objects interact

December 11, 2017 • Describe how charged objects interact with each other by performing a lab and doing a demonstration. • Discuss Coulomb’s law and use it to solve problems.

Drill – Circuits Unit Overview 1. 2. 3. 4. 5. How do you connect a voltmeter and ammeter in a circuit? What is the equation for Ohm’s Law? In a series circuit, what will happen if you unscrew one lightbulb? In a parallel circuit, what will happen if you unscrew one lightbulb? Given the same battery voltage, will 3 lightbulbs glow brighter in series or in parallel? 6. What is the equation for power?

Introduction to Electrostatics Why is it that when you touch metallic objects, especially during winter, you get an electric shock? https: //www. youtube. com/watch? v=yc 2 -363 MIQs

Static Electricity • Air is drier in the winter! • When the air is drier, the charge collects and clings to us, building up until. . . zap! • The charge of atoms is constantly changing as materials and objects make contact and electrons are passed around (or donated). • When a positively charged object gets near a negatively charged object, there is a movement of electrons from the negatively charged object to the positively charged one… zap!

December 12, 2017 • Describe how charged objects interact with each other by performing a lab and doing a demonstration. • Discuss Coulomb’s law and use it to solve problems. • Solve problems on electric charge and force.

Drill 1. An object with an excess of _____ is negatively charged. 2. An object with too few electrons is _____ charged. 3. An object with the same number of _____ and _____ is neutral.

Demonstration - Van de Graaff Generator 1. Troll 2. Students 3. Fluorescent light 4. Bubbles

Lab Procedures Notes: • Attach the rod using both strings – leave 1 cm between strings. • Charge the rods moving in one direction. • Ebonite = hard rubber on the Triboelectric Series

December 13, 2017 • Discuss Coulomb’s law and use it to solve problems. • Solve problems on electric charge and force.

Drill – Take out Yesterday’s Lab Paper 1. What happened when you brought a charged rod (negative or positive) next to the neutral hanging rod? 2. What happened when you brought two negatively charged rods next to each other? 3. What happened when you brought a negatively charged rod and a positively charged rod next to each other?

Three Methods to Charge Objects 1. Charging by friction. 2. Charging by induction. 3. Charging by conduction. We demonstrated all three of these methods yesterday.

Charging by Friction • Lab: wool + rods • Creating friction between two neutral objects causes the neutral material with a greater electron affinity to attract and “steal” electrons from the material with a lower electron affinity. • One material becomes negatively charged, the other becomes positively charged.

Triboelectric Series Low Electron Affinity - Positive High Electron Affinity Negative Asbestos Rabbit Glass Hair Nylon Wool Silk Paper Cotton Hard rubber Synthetic rubber Polyester Styrofoam PVC pipe Teflon Silicone rubber

Charging by Induction • Lab: neutral + charged rods • Bringing a charged object near (not touching) a neutral object polarizes the charges within the neutral object. • Why? ? • Like charges in the neutral object are repelled by the charged object. • Unlike charges in the neutral object are attracted by the charged object.

Charging by Induction

Demonstrations – PVC Pipe + Paper 1. Charging by friction: cloth + PVC pipe become charged. 2. Charging by induction: charged PVC pipe polarizes the paper causing an attraction between the pipe and paper.

Electric Charge Proton • Positively-charged • Charge: q = +e = +1. 60 x 10 -19 Coulombs (C) • Mass: 1. 67 x 10 -27 kg Electron • Negatively-charged • Charge: q = -e = -1. 60 x 10 -19 Coulombs (C) • Mass: 9. 11 x 10 -31 kg

Law of Conservation of Charge • Electric charge is conserved – it cannot be created or destroyed. It can only move from one object to another. • The smallest value of charge an object can have is e = 1. 60 x 10 -19 C. • All values are whole number multiples of e. • You can never find an object that has a charge that is a fraction of e.

Practice Worksheet #1 -3

December 14, 2017 • Discuss Coulomb’s law and use it to solve problems. • Solve problems on electric charge and force.

Drill – Take out Yesterday’s Worksheet 1. Electric charge is quantized. What is the charge (q) of an electron (e-)? Of a proton (e+)? 2. A mass of 1. 97 x 10 -28 kg was added to a neutral ball as it received extra electrons. How much charge was acquired by the ball?

Coulomb’s Law •

Coulomb’s Law • Note: Do not include the signs of the charges in the equation. • Add the direction of the force at the end: • Like charges repel. • Opposite charges attract.

Practice Worksheet #4 -9

December 15, 2017 • Discuss Coulomb’s law and use it to solve problems. • Solve problems on electric charge and force.

Drill 1. When the distance between two charged objects is doubled, what happens to the electrical force they exert from each other? 2. Two charges are attracted by a force of 47 N when separated by 22 cm. What is the force between the charges when the distance between them is 95 cm?

Partner Practice! • If you are a snowman head, find a snowman body. • If you are half a snowflake, find another half of a snowflake. • Classwork will be collected at the end of class. Work together!

December 18, 2017 • Discuss Coulomb’s law and use it to solve problems. • Solve problems on electric charge and force.

Demonstration • The class will demonstrate charging by induction and charging by conduction by using a rod an electroscope. • The class will discuss their observations.

Charging by Conduction • Van de Graff generator • If a charged object is brought in contact with a neutral object, charges will be repelled from (or attracted to) the charged object. • The neutral object will gain a charge of the same sign as the charged object. • This is also called charging by conduction.

Static Electricity • Static Electricity = the build-up of electric charge on the surface of objects. • Electrons move from one surface to another through contact. • If the surfaces are both insulators, they'll build up an electrical charge. One object will have a positive charge and one will have a negative charge. • If one of the charged objects then touches a conductor, the charge will neutralize itself, causing a static shock. • Dry air is also an insulator, so static electricity is even more common during the dry winter months.