1 / 42

560 likes | 2.25k Vues

Chapter 17 Electric Forces and Fields. 17.1 Electric Charge. Objectives Understand the basic properties of electric charge Differentiate between conductors and insulators Distinguish between charging by contact, charging by induction , and charging by polarization.

Télécharger la présentation
## Chapter 17 Electric Forces and Fields

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**17.1 Electric Charge**Objectives • Understand the basic properties of electric charge • Differentiate between conductors and insulators • Distinguish between charging by contact, charging by induction, and charging by polarization**Electrostatics - Properties**• Two kinds of charge: positive negative • Electric charge is conserved • Like charges repel, unlike charges attract • Charges travel between unlike materials**Electrostatics – More Properties**• The fundamental unit of electric charge is denoted by the small letter “e” • An electron has a charge of –e • A proton has a charge of +e • Quantized: Electric charges are always a multiple of e. (+/- 1e, +/- 2e, +/-3e etc.) • Value of e = 1.602 x 10-19 Coulombs and 1.0 C = 6.2x1018electrons**Electrostatics**• Charge was discovered by Robert Millikan (oil drop experiment)**Electrostatics**• Negatively charged drop suspended inside had no net force**Electrostatics - Transfer**• CONDUCTORS – electric charge moves freely • INSULATORS – electric charge does not move freely • Semiconductors • Superconductors**Electrostatics – Methods of Charging**• By contact • Two objects touching each other • Conductors or insulators • By induction • No contact required • Grounding source needed • Conductors only • By polarization • Realignment of charge on surface • Contact or no contact • Insulators only**Triboelectric Series**• Rubbing two different materials together results in the transfer of electrons • The prefix “tribo” means “to rub” • The Triboelectric Series is a list that ranks materials according to their tendency to gain or lose electrons**Charging by Polarization**PhET Interactive, UC-Boulder**Electroscope**• A device that can be used to detect and demonstrate the presence of a static charge**17.2 Electric Force**Objectives • Calculate electric force using Coulomb’s Law • Compare electric force with gravitational force • Apply the superposition principle to find the resultant force on a charge and to find the position at which the net charge is zero.**Coulomb’s Law: Electric Force**Felectric = kC(q1q2) r2 kC = Coulomb constant = 8.99x109Nm2 C2 q1 = charge of charge 1 (C) q2 = charge of charge 2 (C) r = distance between charge 1 & charge 2 (m)**Felectric is a vector quantity**• Magnitude • Direction**Comparison of forces**Electric (Felectric) Gravitational (Fg) Felectric = kCq1q2 r2 Fg = G m1m2 r2 G = gravitational constant = 6.67x10-11 Nm2/kg2 kC = Coulomb constant = 8.99x109 Nm2/C2**Resultant ForceThe sum of all individual vector forces**What is the resultant (net) force C will feel? FAC = 0.067 N A is pushing C away FBC = 0.022 N B is pulling C toward it Fnet-C = FAC – FBC = 0.067 – 0.022 = 0.045 N**Resultant Force – Another Example**A charge of -2.00nC is located at the origin. Another charge of 5.00nC is located at a position x = 4.00m. Another charge of 6.00nC is located at a position y = -3.00m. What is the magnitude and direction of the net force on the 5.00nC charge? ANS: F3 = 7.16nC at an angle of 65.2o**Charges in Equilibrium Example**Bookwork #22, set up**17.3 Electric Field**Objectives • Calculate electric field strength • Draw and interpret electric field lines • Identify the four properties associated with a conductor in electrostatic equilibrium**Electric Field**• Electric Field is the field that permeates the space around a charged object and in which another charged object experiences an electric force • Electric Field is a ratio of Force to Charge E = Felectric / q0 • The direction of E is defined as the direction of the electric force that would be exerted on a small positive test charge (q0)**Electric Field**A vector quantity with….. E = kCq N/C r2 MAGNITUDE determined by: The direction of the force that charge (q) would exert on a small positive test charge placed in it’s vicinity DIRECTION determined by:**Electric Field Lines**• Electric FieldLines are lines that represent both the magnitude and the direction of the electric field. • The number of lines shown is proportional to the electric field strength. As lines get closer together, the field strength increases.**Electric Field Lines – Rules for Drawing**• Lines begin on + charges (or at infinity) and terminate on – charges (or at infinity) • The number of lines drawn leaving a + or terminating on a – is proportional to the magnitude of the charge • No two field lines can cross one another.**Electric Field Lines - Monopoles**The electric field from an isolated positive charge The electric field from an isolated negative charge**Electrostatic Equilibrium**An isolated conductor with no net motion of charge is said to be in a state of…..**Four Properties of Electrostatic Equilibrium**• The electric field is zero inside a conductor 2. Any excess charge resides entirely on the surface of the conductor 3. The electric field just outside a charged conductor is perpendicular to the conductor’s surface 4. On an irregularly shaped conductor, charge tends to accumulate where the radius of curvature is smallest.**Lab – Balloon Electrostatics**• Sum the vectors in the x-direction • Sum the vectors in the y-direction • From the diagram, Felectric can be found • Felectric is equal and opposite Tx (tension) • Q can be found • Finally, the number of electrons can be found

More Related