ANOTHER CIRCUIT ELEMENT. Capacitor Stores electric charge Symbol: Unit: Farad Can be connected in series or in parallel. Example

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1 ANOTHER IRUIT ELEMENT apacito Stoes electic chage Symbol: Unit: Faad an be connected in seies o in paallel A ail gun is a weapon that biefly needs a huge electic cuent in ode to acceleate a pojectile to high speed. The huge cuent is supplied by a collection of lage capacitos. They stoe chage that is spilled into the cicuit to ceate a huge tempoay cuent. onnection in Seies The total capacitance T of seveal capacitos connected in seies is given by T = A 00 Faad capacito and a 300 Faad capacito ae connected in seies. What is the total capacitance? 3 4 = + = + = T 00F So T = = 75F 4

2 onnection in Paallel The total capacitance T of seveal capacitos connected in paallel is given by T = Thee capacitos ae connected in paallel. Thei capacitances ae 700 pf, 650 pf, and 200 pf. What thei total capacitance? pf = picofaad = 0-2 Faad T = 700 pf pf pf = 550 pf MAGNETI FIELDS Magnetic field of a staight wie A cuent in a staight wie poduces a magnetic field that ciculates aound the wie. Imagine that a wie is pependicula to this page. Suppose that it caies a cuent that points out of this page (i.e. it s coming staight at you). Then the magnetic field ciculates aound the wie in the counte clockwise diection. A compass needle at any point on the cicle will be tangent to the cicle. A magnetic field exists at any cicle centeed on the wie. The geate the adius of the cicle, the weake the magnetic field on it. To find the diection in which the magnetic field ciculates, use Right Hand Rule # -- If you point you ight thumb in the diection of the cuent, the finges of you ight hand will cul in the diection of the magnetic field.

3 . A staight wie is pependicula to this page. The cuent in the wie flows into the page (i.e. away fom you). In what diection does the magnetic field ciculate? Answe: lockwise. [Point you ight thumb in the diection of the cuent (into the page). You finges cul clockwise.] Magnetic Field of a coiled wie Fo a long coil, the magnetic field though the cente of the coil is staight and paallel to the coil. Fo a long coil, the magnetic field outside of the coil is staight a paallel to the coil.

4 The diection of the magnetic field though the cente of the coil is opposite of the diection of the magnetic field outside of the coil nea its midpoint. Right Hand Rule #2: To find the diection of the magnetic field though the cente of the coil, cul the finges of you ight hand in the coection of the coil cuent. You ight thumb will point in the diection of the cental magnetic field. [Ty it fo image above.] ANOTHER FORE LAW (Loentz Foce) When an electic chage q is moving with velocity v in a magnetic field B, the foce F that the magnetic field exets on the paticle is given by F qv B =. Right Hand Rule #3: To find the diection of this foce, poceed as follows: ) Align the finges of you ight hand in the diection of v. 2) ul you finges you finges in the shotest diection to B. 3) If q > 0 (positive chage), you thumb will point in the diection of F. If q < 0 (negative chage), you thumb will point in the diection opposite that of F. The velocity vecto v of a poton is instantaneously to the ight. It tavels in a magnetic field B that points downwad as shown. In what diection does the foce on the poton point? Answe: It points into the page. [Follow ight hand ule #3] What is the paticle was an electon? Answe: The foce would point out of the page.

5 Impotant popeties of the Loentz foce: Foce is pependicula to the plane containing the velocity and magnetic field vectos. Foce on an electically neutal paticle is zeo. Foce on a stationay paticle is zeo. Foce on paticle moving paallel to magnetic field lines is zeo Foce causes chaged paticles to move in cicles o spials. [Paticles fom the sun spial towad the Eath s poles to ceate the Auoa Boealis.] Application of the Loentz foce: ail gun Magnetic field between the two ails is pependicula to the diection of cuent (moving chages) that flows though the bullet acoss the ails. Foce popels the bullet fowad.