Version 001 HW#6 - Electromagnetic Induction arts (00224) 1 3 T

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1 Version 001 HW#6 - lectromgnetic Induction rts (00224) 1 This print-out should hve 12 questions. Multiple-choice questions my continue on the next column or pge find ll choices efore nswering. AP 1998 MC points A rectngulr wire loop with n turns is t rest in uniform mgnetic field of mgnitude 3 T tht is directed into the pge. The loop mesures 9 cm y 8 cm, nd the plne of the loop is perpendiculr to the field, s shown. 9 cm 8 cm n turns = 3 T. The mgnetic flux is Φ = A = (3 T)(0.09 m)(0.08 m) = T m 2. Conducting ing points A constnt current is flowing through solenoid, creting mgnetic field. conducting ring V I 3 T Wht is the totl mgnetic flux Φ through the loop? 1. Φ = T m 2 2. Φ = T m 2 3. Φ = T m 2 4. Φ = T m 2 5. Φ = T m 2 6. Φ = T m 2 7. Φ = T m 2 8. Φ = T m 2 9. Φ = T m 2 correct 10. Φ = T m 2 Let : l = 8 cm = 0.08 m, h = 9 cm = 0.09 m, nd The force which the mgnetic field exerts on conducting ring positioned s shown is 1. There is no force, only torque. 2. downwrd. 3. upwrd. 4. There is neither force nor torque. correct The mgnetic field within the conducting ring is constnt since the current flowing through the solenoid is constnt in time. In other words, there is no induced current in the conducting ring. Therefore, no force nor torque is exerted on the conducting ring. Holt SF 22ev points Aflexileloopofconductingwirehsrdius of 0.16 m nd is perpendiculr to uniform

2 Version 001 HW#6 - lectromgnetic Induction rts (00224) 2 mgnetic field with strength of 0.36 T, s shown. = 1(0.36 T)cos0 ( m 2 ) 0.17 s = V. Serwy CP (prt 1 of 3) 10.0 points The loop is grsped t opposite ends nd stretched until it closes to n re of m 2. Two coils re suspended round common centrl xis s shown in the figure elow. One of the coils is connected to resistor with ends leled nd. The other coil is connected to ttery through switch S. Use Lenz s lw to nswer the following question concerning the direction of induced currents. Find the mgnitude of the verge emf induced in the loop during the 0.17 s it tkes to close the loop. Correct nswer: V. + S Let : N = 1, r i = 0.16 m, A f = m 2, = 0.36 T, t = 0.17 s, nd θ = 0. Wht is the direction of the mgnetic field inthecoilsfter theswitchisclosedfor long period of time? 1. The mgnetic field is zero. 2. right to left ( = ) correct 3. left to right ( = ) A i = πr 2 = π(0.16 m) 2 = m 2, so A = A f A i = A f πr 2 i = m m 2 = m 2 nd The smller helicl coil produces counterclockwise current (looking from left-hnd end of the coil). Using the right-hnd rule, when the switch is closed, the mgnetic field is directed from right to left ( = ). = N A cosθ t = N cosθ A t 005 (prt 2 of 3) 10.0 points After switch S hs een closed for long period of time, the switch is opened.

3 Version 001 HW#6 - lectromgnetic Induction rts (00224) 3 Wht is the direction of the internl induced mgnetic field y the lrger dimeter (secondry) coil just fter the switch is opened? 1. left to right ( induced = ) is connected to resistor with ends leled nd. The other coil is connected to ttery. The coils re moving reltive to ech other s indicted y the velocity vectors v right to left ( = induced ) correct 3. The mgnetic field is zero. The induced mgnetic field depends on whether the flux is incresing or decresing, since y Lenz s lw the induced current will produce flux to oppose chnge in flux. When the switch is closed, there is mgnetic field. At the moment the switch is opened, the mgnetic flux through the coils decreses. The induced field through the coil in the circuit with resistor must produce mgnetic field from right to left ( = induced ) to resist ny chnge of flux in the coil (Lenz s lw). 006 (prt 3 of 3) 10.0 points Whtisthedirectionofthecurrentinducedin the resistor just fter the switch is opened? 1. from through to (I ) 2. from through to ( I) correct 3. The induced current is zero. The lrger helicl coil is wound counterclockwise (looking from left-hnd end of the coil) from terminl to terminl. Using the right-hnd rule, when the induced mgnetic field is right to left ( = induced ), theinduced current throughthe resistor flows from through to ( I). Serwy CP (prt 1 of 3) 10.0 points Two coils re suspended round centrl xis s shown in the figure elow. One coil v v Wht is the direction of the mgnetic field in the coil with the ttery ttched? 1. The primry field is zero. 2. right to left ( = primry ) correct 3. left to right ( primry = ) The helicl coil with the ttery ttched (when viewed from either end) is wound clockwise (s you go into the coil). Using the right-hnd rule, the mgnetic flux through the coil with the ttery ttched hs mgnetic field direction right to left. 008 (prt 2 of 3) 10.0 points Wht is the direction of the induced mgnetic field in the coil with the resistor ttched when thethe coilsremovingwy from ech other? 1. right to left ( = induced ) correct 2. The induced field is zero. 3. left to right ( induced = ) The induced mgnetic field depends on whether the flux is incresing or decresing.

4 Version 001 HW#6 - lectromgnetic Induction rts (00224) 4 + copper wire. Initilly, uniform mgnetic fieldofmgnitude i pointshorizontllyfrom left-to-right through the perpendiculr plne of the coil. primry induced Themgneticfluxthroughthecoilwiththe ttery ttched is from right to left. When thecoilsremovingwyfromechother,the mgnetic flux from the coil with the ttery ttched decreses its intensity in the coil with the ttched resistor. The induced current in the coil must produce n induced mgnetic field from right to left ( = induced ) to resist ny chnge of mgnetic flux in the coil (Lenz s Lw). 009 (prt 3 of 3) 10.0 points Wht is the direction of the induced current in resistor when the coils re moving wy from ech other? 1. The induced current is zero. 2. from through to ( I) 3. from through to (I ) correct The helicl coil with the resistor ttched (when viewed from either end) is wound clockwise (s you go into the coil). Since the induced field is right to left ( = induced ) the induced current in the coil flows clockwise when viewing the coil from the right-hnd side. Therefore the current flows from through to (I ). Circulr Copper Coil points A circulr coil is mde of N turns of copper wire s shown in the figure. When viewed from the right the coil is wound counterclockwise. A resistor is inserted in the Mgnetic Field (t) During time intervl t the field uniformly chnges t constnt rte, until reversed field is reched equl in mgnitude to the initil field. The current in the resistor 1. flows from left to right. correct 2. is zero. 3. flows from right to left. 4. flows in direction tht cnnot e determined from the informtion given. As the left-to-right mgnetic field decreses (nd eventully flipping sign nd incresing in mgnitude) it follows from Lenz s lw (opposition to the chnge in mgnetic field will tend to keep the current constnt nd flowing in the sme direction) tht the induced emf will produce left-to-right mgnetic field rising from induced currents in the coil. y the right hnd rule, the induced current flows counter-clockwise when viewed from the right nd the coils re wound counterclockwise s the wire goes from the right to left terminls. The current must enter the loop from the right terminl nd exit t the left terminl. Since the current is continuous, the current must flow through the resistor in the left-toright direction. Conceptul 17 Q points

5 Version 001 HW#6 - lectromgnetic Induction rts (00224) 5 Ar mgnetisdropped, northpoledown, so tht it flls through circulr piece of wire, s shown. S N Wht is the direction of the induced current in the loop efore it psses through the wire (viewed from top)? After it psses through? 1. counterclockwise; counterclockwise 2. Unle to determine 1. the mgnet one 2. the nonmgnetic one correct 3. oth t the sme time The mgnetic field of the moving mgnet produces the induced current round its copper tue. Menwhile, the induced current cuses its mgnetic field inside the copper tue. The kinetic energy, hence the speed of the mgnetic r must decrese to generte thecurrent inthetueduetoconservtionof nergy. The overll effect, therefore, is tht the mgnetic field creted y the induced current retrds the mgnet inside so tht the nonmgnetic r will strike the ground first. 3. counterclockwise; clockwise correct 4. no induced current 5. clockwise; counterclockwise 6. clockwise; clockwise efore the r mgnet psses through the wire, the mgnetic field points downwrd nd is incresing, so the induced current would crete mgnetic field directed upwrd. The direction of the induced current should e counterclockwise. After the r mgnet psses through the wire, the mgnetic field points downwrd nd is decresing, so the induced current would crete mgnetic field directed downwrd. The direction of the induced current should e clockwise. Tower of Pis points Imgine tht Glileo hd dropped r mgnet nd nonmgnetic r of the sme mss nd shpe down identicl copper tues from the Tower of Pis. Which one would hve struck the ground first?