# The study of electrical charges.  Two possible states of charge:  Positive and negative ▪ Named by Benjamin Franklin ▪ He decided what was considered.

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The study of electrical charges

 Two possible states of charge:  Positive and negative ▪ Named by Benjamin Franklin ▪ He decided what was considered “positive” and what was “negative”  When 2 objects are rubbed together, one becomes “positive” and one becomes “negative”…electrons are transferred from one object to another.  Flow of electrons = electricity

 Insulators: materials that charges do not easily move through.  Plastic, rubber, dry wood, glass  Conductors: materials that allow charges to move.  Examples: metals…copper, zinc, nickel, lead

 Electric forces are the interaction of charged particles.  Things to note:  2 kinds of electrical charge: positive and negative  Charges exert force on other charges over a distance  Like charges repel…opposite charges attract.

 Charging a neutral body by touching it with a charged conductor. Electrons transfer to or from the conductor.  The charge spreads throughout the neutral body.

 A charged rod is held near a conductive material. Like charges repel, opposites attract.  Material is grounded to allow transfer of electrons to earth.  Ground then removed.  Grounding: touching an object to Earth to eliminate excess charge.  Lightning rods, grounding gas trucks, etc.

 Read Section 16.1 (pages 558-563)  Do Section Review #1-6

16.2

 Charles Coulomb  Worked with charged spheres to understand relationships between charge, distance, and force.  Found that: ▪ F α 1/d 2 ▪ F α qq’  Coulomb’s Law  K = 9.0 x 10 9 N*m 2 /C 2  q = charges (In Coulombs (C))  d = distance (meters)

 1 Coulomb = the charge of 6.25x10 18 electrons  1 Electron = 1.6x10 -19 C

 Object A has a positive charge of 6.0x10 -6 C. Object B, carrying a positive charge of 3.0x10 - 6 C, is 0.03 m away.  A. What is the force on A?  B. What would be the force on A if the charge on B were negative?

 Object A has a 6.0x10 -6 C charge and has 2 other charges nearby. Object B is 0.04 m to the right of A and has a charge of -3x10 -6 C and object C is 0.03 m directly below A and has a charge of 1.5x10 -6 C. What is the net force on A?

 Pg. 566 #1,3  Pg. 568 #2ab  Pg. 570 #1-2  Pg. 571 #1,3,4

16.3

 Concept of electric field developed by Michael Faraday  A charge creates an electric field about it in all directions.  A 2 nd charge inserted into the field interacts with the field at that point.

 Only observed by measuring impact on other charged particles.  A small positive test charge is placed a certain distance away

 Electric fields are always considered using a small positive test charge  Electric field lines show the direction of the electric field radiating from a charge.  When considering electric fields produced from multiple charges, the field lines become curved and more complex.

 Homework:  Pg. 575 #1-2  Pg. 581-585  #3,5,15,18,21,24,31,32,34,35,41,45,46

Section 17.1

 The work done on moving a charged particle in an electric field can result in the particle gaining potential or kinetic energy.  Pe electric = -qEd (in uniform electric field)

 Electric potential increases as positive test charge is separated from negative charge  Electric potential increases as positive test charge is moved toward positive charge.

 Change in potential energy per unit charge  Measured in J/C = V  V = Volt  ΔV = ΔPE/q’  Reference level for zero potential in a field is arbitrary

 Only differences in electric potential are important  Potential difference  Measured with a voltmeter  Often called “voltage”  V = V B - V A

 Uniform field can be produced by oppositely charged conducting parallel plates.  ΔPE = +Fd  V = +Fd/q = +(F/q)d  E = F/q  V = Ed

 All systems reach equilibrium when energy is at a minimum.  Charges on 2 objects try to spread out to reduce electrical potential.  Grounding: touching an object to Earth to eliminate excess charge.  Lightning rods, grounding gas trucks, etc.

 Charges spread out as far apart as possible  A Hollow conductor will have all charges on outside surface. ▪ Shields the inside from electric current ▪ People in a car with power lines across it.

 Pg. 599 #1-3  Pg. 601 #5-9  Pg. 626-630 #9, 59, 61, 62, 64

 Capacitance (C)  = the ratio of charge to potential difference  C = q/V  Measured in farads (F)…1 F = 1C/V  A device designed with a specific capacitance is a capacitor.  Made of 2 conductors with equal and opposite charge separated by an insulator.  Most capacitors are between 10 picofarads and 500 microfarads.

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