Phys 115 1st Edition Lecture 6Outline of Last Lecture I. Reynolds NumberOutline of Current Lecture II. Electric chargeIII. Electric forces and Coulomb’s lawIV. Electric fieldsCurrent Lecture- Textbook reviewo There are positive and negative chargeso Like charges repelo Opposites attracto Fundamental charge e = 1.6 *10-19 coulombs (C)o Neutral objects have both positive and negative charges- Coulomb’s Lawoo K = 9 *109 N-m2/C2o r12 = distance between chargeso This is the force exerted by q1 on q1- CR1o B < A = Co Use Coulomb’s Lawo Increase by 2, decrease by 22 FnetB is ½ FnetAo Increase by 4, decrease by 22 FnetC = FnetA- CR2o The same because of Newton’s 3rd law- CR3o D < B < C < Ao In D the charge goes both ways, so it is equal and the magnitude is 0o In C the charge goes to the left.o In B the charge goes to the left.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o The magnitude of C is larger than B because the two forces are in the same direction, so it goes left more. o In A, the charges both go to the right.- Textbook Reviewo The electric force can be modeled in terms of an electric field that describes how a charge modifies space around it.o The magnitude of the electric field created by a charge is the magnitude of the force exerted on a test charge divided by the magnitude of the test charge:oo Magnitude of electric field created by a point charge Q, at a location a distance r away from the charge:oo Direction of field: away from charge Q if Q is positive, toward charge Q if Q is negativeo Same direction as force exerted on a positive test charge at that locationo Units: N/C- CR5o 1) net =1o 2) net = ½o 3) net = 2o 4) net = ¼o 4<2<1<3- CR6o 1) lefto 2) right, field due to positive is larger because it’s closero 3) lefto 4) 0 because opposite forces cancel out- CR7o D because you add the two vectors- CR11o Electric field direction is zero- Conductors and Insulatorso Inside a conductor, the electric field is zero, otherwise the molecules would movearound; charges can’t move moleculeso Electric field is the same along plateso- CR12o Conductors provide shielding from electric
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