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# Q y inside dielectric 0 a physics 2b

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Unformatted text preview: avior of two element circuits and calculate the time at which events occur in DC. Evaluate the frequency dependence in AC circuits using impedance. Determine the value of resonance frequency. Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 28   Up to now we have almost always dealt with electrostatics, which is no moving charges.   Now we are going to discuss moving charges.   This takes a little more defining than you might think/want.   Definition: current is the movement of positive charge in a certain direction.   Why that is silly? Electrons are the things moving.   However, Benjamin Franklin couldn’t know this.   SI Units: Ampere, A C [I ] = A = s Physics 2B - Summer Session 2 - C. Palmer dQ I= dt August 19, 2013 29   Current is made by many charged objects moving through a piece of material.   The charge density is the current per unit area through any element of cross section.   If the charges are positive, then J is in the same direction as the individual particle velocities.   And the opposite direction if they are negative. I = ∫ J ⋅dA Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 30   The average charge density through a slice of element of cross section is current divide by the area at that position. J Average I = A Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 31   A conductor in the shape below has constant current flowing through it. Which of the following is true? A)  The average current density is constant. B)  The average current increases from left to right. C)  The average current density increases from left to right. D)  The average current density decreases from left to right. Physics 2B - Summer Session 2 - C. Palmer J Average August 19, 2013 I = A 32   A conductor in the shape below has constant current flowing through it. Which of the following is true? A)  The average current density is constant. B)  The average current increases from left to right. C)  The average current density increases from left to right. D)  The average current density decreases from left to right. Physics 2B - Summer Session 2 - C. Palmer J Average August 19, 2013 I = A 33   When a conductor has a current passing through it, the electrons move randomly, but they tend to drift with a drift speed vd in the direction opposite that of the applied electric   The equivalent drift of positive charge carriers field that causes the is in the direction of the current. The drift speed is applied electric field, E, tiny compared with the is pictured. speeds in the random motion. N = nAL Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 34   Total charge carriers N = nAL   Total charge q = ( nAL ) e L   Time to travel L t= vd   Current q nALe I= = = nAevd L t vd Physics 2B -...
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