Static Electricity Created by Craig Smiley (Harrison HS, West Lafayette, IN) Supported by grant PHY-0851826 from the National Science Foundation and by Purdue University

Lesson 1 – Ways of Charging

Interaction of Charged Objects A neutral object made of a conductive material is by itself, and the model of the arrangement of electrons and protons in the crystal lattice looks like this.

Interaction of Charged Objects If a negatively charged object was brought near the neutral object made of a conductive material, what would it look like?

Interaction of Charged Objects If a negatively charged object was brought near the neutral object made of a conductive material, what would it look like? A. B. C. D.

Interaction of Charged Objects If a negatively charged object was brought near a neutral object made of an insulative material, what would it look like? A. B. C. D.

Interaction of Charged Objects Will a neutral object be attracted to a positively charged object that is brought close to it? Yes No, it will repel No, it will do nothing Depends on the material

Interaction of Charged Objects Two socks are taken out of the dryer and they stick together due to static cling. Which of the following statement(s) describe(s) why this occurs? The socks have the same type of charge The socks have opposite type of charges One sock is positively charged and the other is neutral One sock is negatively charged and the other is neutral A, C, and D are possibilities B, C, and D are possibilities

Charging by Friction If you charged a metal sphere by friction, where on the sphere would it be charged? Throughout the entire volume of the sphere and the charge would be equally dispersed. Throughout the entire volume of the sphere but the charge would be more concentrated where it was rubbed. Over the entire surface area of the sphere (nothing in the middle) and the charge would be equally dispersed. Over the entire surface area of the sphere (nothing in the middle) but the charge would be more concentrated where it was rubbed. Only where it was rubbed. Depends if it was positively or negatively charged.

Charging by Friction If you charged a rubber sphere by friction, where on the sphere would it be charged? Throughout the entire volume of the sphere and the charge would be equally dispersed. Throughout the entire volume of the sphere but the charge would be more concentrated where it was rubbed. Over the entire surface area of the sphere (nothing in the middle) and the charge would be equally dispersed. Over the entire surface area of the sphere (nothing in the middle) but the charge would be more concentrated where it was rubbed. Only where it was rubbed Depends if it was positively or negatively charged.

Charging by Conduction What happens when a positively charged object touches a neutral conductor? Extra protons from the charged object jump over to the neutral conductor making the conductor positively charged. Electrons from the positively charged object jump over to the neutral conductor making the conductor negatively charged. Electrons from the neutral conductor jump over to the positively charged object making the conductor positively charged. The charged particles polarize, but the conductor does not become charged. None of these

Charging by Induction What happens when a neutral conductor is charged by induction by a negatively charged object? Electrons from the charged object jump over to the neutral conductor making the conductor negatively charged. Electrons from the neutral conductor jump over to the charged object making the conductor positively charged. Electrons from the conductor go to ground leaving the conductor positively charged. Electrons from the ground go to the conductor making it negatively charged. Protons from the ground go to the conductor making it positively charged.

Charging by Induction You are standing under an thundercloud, which has strong negative charge. You touch a metal fence post with your knee and experience a little shock. Assuming the fence post was neutral b/c it is in the ground and your feet are not in contact with the ground b/c you are wearing tennis shoes, what is the charge on you after the shock? Positive Negative Neutral Can’t be determined

Coke can & rubber rod After hmwk: VdG gen & hair Lesson 2 – Coulomb’s Law Coke can & rubber rod After hmwk: VdG gen & hair

Charge on an object What does it mean if an object has a charge of -1C ? It has 1 electron It has 1 more electron than it has protons It has 6.25x1018 electrons It has 6.25x1018 more electron than it has protons None of these

Charge on an object In chemistry you would say that Magnesium (Mg) would like to lose two electrons to be stable, which could be written like Mg+2 How many Coulombs of charge would that be on the Magnesium atom? +2C +2μC +1.25x10-18 C Can’t be determined

Coulomb’s Law Two equal packaging peanuts are charged, and hang on strings as shown. What can you conclude about the signs of the charges q1 and q2 on the two packaging peanuts? Both are + Both are – One is + and the other is – Both must be the same charge (but if they are both + or both – can’t be determined) Can’t be determined

Newton’s 3rd Law Which is experiencing a greater gravitational force? Earth Moon The same

Coulomb’s Law Two identical uniformly charged spheres, and the charge on sphere 2 is three times the charge on sphere 1. Which force diagram correctly shows the magnitude and direction of the electrostatic forces? A. B. C. D. E.

Coulomb’s Law Two equal packaging peanuts are charged, and hang on strings as shown. What can you say about the magnitudes of the charges q1 and q2 on the two packaging peanuts? q1 = q2 q1 ≠ q2 Can’t be determined

Coulomb’s Law There are three charged objects in a line that indicate the sign of their charges but not their magnitudes. The net force on charged object 2 is directed to the: Right Left Can’t be determined

Coulomb’s Law There are three charged objects in a line that indicate the sign of their charges but not their magnitudes. The net force on charged object 3 is directed to the: Right Left Can’t be determined

Coulomb’s Law There are three charged objects in a line that indicate the sign of their charges but not their magnitudes. The net force on charged object 1 is directed to the: Right Left Can’t be determined

Coulomb’s Law Object A has a charge of +4C and is near Object B, which has a charge of -3C. Object B is then replaced with Object C, which has a charge of +6C. What happened to the electrical force on Object A? Doubled and same direction Doubled and opposite direction Tripled and opposite direction Quadrupled and same direction E. None of these A B C A

Coulomb’s Law Two charged objects are a certain distance apart. If you move them away from each other so they are now 4x the distance as they were originally, what happened to the electrical force between them? Increased by 16x Increased by 4x Decreased to 1/2 Decreased to 1/4th Decreased to 1/16th None of these A B A B

Lesson 3 – Electric Field Van de Graff & peanut After hmwk: VdG gen & pie tins

Electric Field What is always present around a charged object? An electrical force An electric field Both of these None of these

Electric Field What happens to the strength of the electric field created by an object with a charge of –Q as you move away from it? -Q Increases linearly Increases more than linearly Stays constant Decreases linearly Decreases more than linearly

Electric Field Lines What is the correct diagram for the electric field lines illustrating the electric field around a negatively charged object? A. B. C. D.

Electric Field Which is the correct direction of the electric field at the location x in space created by an object with a charge of +Q? A. B. C. D. E. +Q . x

Electric Field A negatively charged peanut is repelled from an object with an unknown charged object. What is the direction of the electric field created by this unknown charged object. Inward, towards the charged object Outward, away from the charged object Can’t be determined

Electric Field What is the direction of the Electric field at the midpoint between the two identically charged objects? ↑ ↓   No Electric field

Electric Field Which sketch best shows the Electric field around two oppositely charged objects? A B D C

Capacitor If there are two oppositely charged plates made of a conducting material, then a uniform Electric field is created between them. What is the charge on each plate? Left: + Right: – Left: – Right: + Left: + Right: + Left: – Right: –

Capacitor If an electron is initially released from rest in the Electric field made by the capacitor, which way will it be forced? ↑ ↓   It will stay at rest

Electric Field If a proton is initially released from rest in the Electric field, which way will it be forced? ↑ ↓   It will stay at rest

Electric Field If a proton is initially released from rest in the uniform Electric field, how will it move? at a constant velocity at a constant acceleration C. neither of these D. can’t be determined

Lesson 4 – Electric Potential Van de Graaff Generator in a line Steel Wool & Cord

Disclaimer! In this class we are going to simplify things and just worry about the interaction between electrons. Because of this electric potential energy will always be considered to be a positive value, and negatively charged objects will want to go from a high electric potential to a lower electric potential. This is different than what you will learn in college! But I believe this will give you a better conceptual understanding of electricity.

Electric Potential Energy There are two electrons separated by a certain distance . In which arrangement is there more electric potential energy? A. B. C. Same D. can’t be determined

Electric Potential Energy vs Electric Potential The two objects shown have the same electron density. The dots represent electrons. Which object has a more electric potential energy? 1 2 Both have the same Can’t be determined 2 1

Electric Potential Energy vs Electric Potential The two objects shown have the same electron density. (The dots represent electrons.) Which object has a higher Electric Potential? 1 2 Both have the same Can’t be determined 2 1

Electric Potential Energy vs Electric Potential Which object has a higher Electric Potential? 3 4 Both have the same Can’t be determined 4 3

Electric Potential Energy vs Electric Potential Is it possible for Object 4 to have more electric potential energy (PE)? Yes, it has to have more PE Yes, it is possible No, they have the same PE No, it has to have less PE 4 3

Electric Potential Difference Which pair of objects has a greater Electric Potential Difference? (Objects 1 & 2 have the same electron “crowdedness”) 1 & 4 2 & 4 3 & 4 Can’t be determined 3 4 4 1 2 4

Electric Potential Difference Which pair of objects has a greater Electric Potential Difference? (Objects 1, 2 & 3 have the same electron “crowdedness”) 1 & 4 2 & 4 3 & 4 All the same Can’t be determined 4 1 2 4 4 3

Shocking 3 1 2 4 4 4 Which pair is most likely to get shocked? (Objects 1 & 2 have the same electron “crowdedness”) 1 & 4 2 & 4 3 & 4 Can’t be determined 3 4 4 1 2 4

Shocking Electrons continue to transfer until when? Each object has the same number of electrons Each object has the same electron density When ALL the electrons have transferred When the Electric Potential is equal to zero None of these

Shocking Which pair will experience a more painful shock? (Objects 1 and 2 have the same electron “crowdedness”.) 1 & 4 2 & 4 Both the same Can’t be determined 2 4 4 1

Is in a car a safe place to be during a lightning storm? Yes, b/c of the rubber tires Yes, b/c of the metal frame No, b/c of the rubber tires No, b/c of the metal frame No, it doesn’t matter, you’re just as at risk inside your car as you are outside

Lightning Rods What is the point of a lightning rod? To give lightning an attractive place to strike and send the bolt along the cable along the outside of the building to the ground, rather than the building. To prevent lightning from striking. Both of these Neither of these