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Circuit Lab

Circuit Lab. Practice #6—Electric Charge, Fields, and Capacitors Mr. Burleson geaux15@hotmail.com. Agenda. 15 minutes—Grading homework. 30 minutes—Learning Lesson of the Day 15 minutes—In Practice quick test on Lesson of the Day 25 minutes—Practical testing 5 minutes—Sending out homework.

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Circuit Lab

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  1. Circuit Lab Practice #6—Electric Charge, Fields, and Capacitors Mr. Burleson geaux15@hotmail.com

  2. Agenda • 15 minutes—Grading homework. • 30 minutes—Learning Lesson of the Day • 15 minutes—In Practice quick test on Lesson of the Day • 25 minutes—Practical testing • 5 minutes—Sending out homework

  3. What is an electric charge? Electric field lines are drawn as radiating from a positive (+) charge and towards a negative (-) charge. Electric fields can be drawn as below. • Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. • There are two types of electric charges; positive and negative (commonly carried by protons and electrons respectively). Like charges repel and unlike attract. An object with an absence of net charge is referred to as neutral • Charge is in unit Columbs (C) , it is always conserved • An electron has a charge of 1.602 x 10-19 C https://en.wikipedia.org/wiki/Electric_charge

  4. Coulomb’s Law • Coulomb’s Law determines the force of attraction of repulsion between two charges. • F is the force in Newtons • ke is Coulomb’s constant 8.99 x 109 N-m2/C2 • q1 and q2 are the charges in Coulombs • r is the distance in Meters between the centers of charges • Groups of charges can be combined into an equivalent charge (i.e. like for an ion) https://en.wikipedia.org/wiki/Coulomb%27s_law

  5. Capacitors(Division C Only) • A capacitor is a passive two-terminal electrical component that stores potential energy in an electric field • Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium (glass, ceramic, plastic, paper, mica, etc.). A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. • Unit of capacitance is a Farad (F). Most capacitors have small values like μF, pF, etc. Charge equals Capacitance times Potential • Q = C V https://en.wikipedia.org/wiki/Capacitor https://courses.physics.illinois.edu/phys102/sp2013/lectures/lecture7.pdf

  6. Capacitors(Division C Only) • A capacitor consists of two conductors separated by a non-conductive region where charge builds up on both sides • When charging the current flows freely at first so it appears to be a short (with zero voltage) • When fully charged the current is completely stopped so it appears to be an open (with maximum voltage). • A capacitance of one Farad (F) means that one Coulomb of charge on each conductor causes a voltage of one Volt (V) across the device • Q = C V https://en.wikipedia.org/wiki/Capacitor https://courses.physics.illinois.edu/phys102/sp2013/lectures/lecture7.pdf

  7. Capacitors(Parallel Plate Model) • The simplest model of a capacitor consists of two parallel plates with a thin dielectric in between. • The dielectric is much thinner than the dimensions of the plates • The dielectric permittivity (ε) of the material determines how much capacitance can be held • C = ε A / d • Energy stored in a capacitor is E = ½ CV2 • Free space/vacuum has a permittivity of εo = 8.854 x 10-12 F/m, all other materials are higher https://en.wikipedia.org/wiki/Capacitor https://courses.physics.illinois.edu/phys102/sp2013/lectures/lecture7.pdf

  8. In Practice Quiz • What are conducting materials? Two examples? • What are insulating materials? Two examples? • What are semi-conducting materials? Two examples? • Draw Electric Field lines for the following charges, show attraction or repulsion - - + - - - + - + - - - + - + - - - + - - - + - - - + -

  9. In Practice Quiz • V = 100 V • R1 = 100Ω • R2 = 220Ω • R3 = 680Ω • What is the voltage drop across each resistor?

  10. In Practice Quiz • If two electrons are 1 mm apart, answer the following: • Are they attracted or repulsed? • What is the force between them? • Draw an electric field diagram not to scale • If two protons are 1 mm apart, answer the following: • Are they attracted or repulsed? • What is the force between them? • Draw an electric field diagram not to scale • If an electron and a proton are 1mm apart, answer the following: • Are they attracted or repulsed? • What is the force between them? • Draw an electric field diagram not to scale

  11. Homework • Know what common materials are used to charge materials (silk cloth, glass, etc.) and which provide positive and which provide negative charges? • Explain how a balloon that is rubbed on someone’s head sticks to the ceiling? • What are common ways to prevent static charge or discharge? • Draw the electric field lines for positive, negative, and mixed charges • Determine the force between a 10C and a -100C set of charges that are 1 m apart (repulsed or attracted?)

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