Physics 72: Chapter 29 Problem Set Name: Lecturer: Mr Carlos Baldo III
Summer 2010 Score: Section: X7-7
Encircle the letter of the correct answer. Solve each problem clearly and completely for full credit. For the next three numbers, consider a circuit, lying flat on this page, which consists of a resistor and a wire. A bar magnet M is moved towards the page, into the loop, causing a current in the resistor directed to the right. 1.
Induced Field. What is the direction of the increasing magnetic field induced by the current? A. Out of the page B. Into the page C. Clockwise D. Counterclockwise E. No magnetic field induced
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External field. What is the direction of the increasing magnetic field that causes the induction effect? A. Out of the page B. Into the page C. Clockwise D. Counterclockwise E. No magnetic field
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Which A. B. C. D. E.
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Lenz Law. “The direction of any magnetic induction effect is such as to oppose the cause of the effect.� This is just another way of saying that magnetic induction must not violate the ________________. A. law of conservation of symmetry B. law of conservation of charge C. law of conservation of energy D. principle of superposition E. the right hand rule
pole of the bar magnet went through the loop first? South pole North pole The magnet has no polarity. Can be south or north pole. It depends on the value of the resistance.
For the next two numbers, consider the setup shown, with the switch S initially closed. 5.
Induced Magnetic Field. If the switch S is opened, what is the direction of the magnetic field induced at the area surrounded by the small circular wire? A. Upward B. Downward C. Out of the plane of the page D. Into the plane of the page E. There is no magnetic field induced.
6.
Induced current. What is the direction of the induced current in the small circular wire? A. Out of the plane of this page B. Into the plane of this page C. Clockwise D. Counterclockwise E. No induced current
Physics 72: Chapter 29 Problem Set 7.
Summer 2010
EMF. Shown at the right is a plot of the magnetic flux ϕ(t) as a function of time t. Let X, Y, and Z be instances when you want to know the electromotive force ε(t). Arrange the emf you measured from largest to least. (Be careful with the signs.) A. ε(X) > ε(Z) > ε(Y) B. ε(Y) > ε(X) > ε(Z) C. ε(Y) > ε(Z) > ε(X) D. ε(Z) > ε(X) > ε(Y) E. ε(Z) > ε(Y) > ε(X)
For the next three numbers, consider a flexible circular conducting loop that is placed inside another larger wire loop with a fixed current I. The two loops are placed on the same plane. An observation point P is located inside the small circular loop. 8.
Magnetic Field. What can be said about the magnetic field at Point P due to the current I passing through the larger loop? A. Constant, and is directed out of the page B. Constant, and is directed into the page C. Increasing, and is directed out of the page D. Increasing, and is directed into of the page E. Decreasing, and is directed Into of the page
9.
Compressed. If the area of the inner flexible loop is decreasing, which of the following statement/s is/are TRUE? Note: assume that point P is still inside the small flexible loop A. The magnetic field at point P decreases B. The magnetic flux through the smaller loop increases C. The magnetic flux through the smaller loop decreases D. A and B E. A and C
10. Induced current. What is the direction of the induced current in the flexible loop? A. Clockwise B. Counter-clockwise C. Into the page D. Out of the page E. No induced current 11. Electric Field. Which of the following statements is always true? A. If there is a magnetic field, there is always an induced electric field. B. If there is an electric field, it is always due to a charge distribution. C. To induce an electric field in a circuit, the circuit/conducting loop must always be immersed in a changing magnetic field. D. The conductor does not need to form a complete circuit or loop to have an induced electric field. E. An induced electric field will exert on a test charge a force whose direction is perpendicular to itself (induce electric field). For the next two numbers, consider a metallic Chicken Lil (of neutral charge) stands atop a metallic Penguin (of neutral charge) which moves at a constant velocity v in a region with a uniform magnetic field directed out of the page. Note: assume that Chick Lil is standing firmly even if Penguin moves. 12. Polarization. Describe how the positive and negative charges are distributed in the given system? A. Positive charges are drifted towards Penguin’s feet B. Negative charges are drifted towards Penguin’s feet C. Positive charges are drifted towards Penguin’s left hand D. Negative charges are drifted towards Penguin’s left hand E. The charges are uniformly distributed to Chick Lil and Penguin.
Physics 72: Chapter 29 Problem Set
Summer 2010
13. Induced electric field. What is the direction of the induced electric field? A. Chick Lil’s head towards Penguin’s feet. B. Penguin’s feet towards Chick Lil’s head. C. From Penguin’s left hand towards his right hand. D. From Penguin’s right hand towards his left hand. E. From Penguin’s bulging tummy towards his back. For the next two numbers, consider a metallic circular disk immersed in a uniform magnetic field directed out of the page. 14. Motional EMF. If the positive charges accumulated at the edges and the negative charges accumulated at its center/axis due to the disc’s motion, the disc must be __________. A. rotating clockwise B. rotating counterclockwise C. moving into the page D. moving out of the page E. moving into the bottom of the page 15. Induced E field. The electric field induced in the circular disk is directed _________. A. Clockwise B. Counter-clockwise C. Radially inward D. Radially outward E. No induced electric field 16. Ampere’s Law. Consider a parallel plate capacitor with current ic
∫ B • dl
along the which varies with time. What is the value for path/Amperian loop represented by the broken line? A. Can be non-zero but always a real number. B. Can be non-zero but always an imaginary number. C. Always zero because there is no magnetic flux enclosed. D. Always zero because there is no electric flux enclosed. E. Always zero because there is no enclosed current. 17. Fluxness. The magnetic flux through a loop changes in time, as shown in the graph below. At which of the three indicated time instants (P, Q, and R) is/are the induced emf in the loop maximum? A. P only B. Q only C. R only D. Q and R only E. P, Q and R For the next two numbers, consider an ultrathin metallic bar of length L lying on the parallel rails of a U-shaped conductor is moving with a velocity v in a region of uniform magnetic field B directed to the right. 18. Force. A. B. C. D. E.
What is the direction of the magnetic force acting on a positive charge in the metallic bar? Into the page Out of the page To the right To the left No magnetic force
19. EMF. What is the value of the induced emf produced across the bar’s ends? A. vBL B. v2BL C. vBL2 D. vB/L E. zero
Physics 72: Chapter 29 Problem Set
Summer 2010
For the next two numbers, consider a square conducting coil that moves in a region of uniform magnetic field directed out of the page. 20. Feel the field. Describe the direction of the induced magnetic field when the coil: (I) is entering, (II) is already inside and (III) is leaving the region of uniform magnetic field. A. (I) Zero, (II) Zero, (III) Zero B. (I) Zero, (II) Into the page, (III) Zero C. (I) Zero, (II) Out of the page, (III) Zero D. (I) Out of the page, (II) Zero, (III) Into the page E. (I) Into the page, (II) Zero, (III) Out of the page 21. Current varies. Describe the direction of the induced emf when the coil: (I) is entering, (II) is already inside and (III) is leaving the region of uniform magnetic field. A. (I) Zero, (II) Zero, (III) Zero B. (I) Zero, (II) Clockwise, (III) Zero C. (I) Zero, (II) Counter-clockwise, (III) Zero D. (I) Counter-clockwise, (II) Zero, (III) Clockwise E. (I) Clockwise, (II) Zero, (III) Counter-clockwise For the next two numbers, consider the figure below showing four wire loops, with edge lengths of either L or 2L. All four loops will move through a region of uniform magnetic field B directed out of the page at the same constant velocity v. 22. Polarization. Which of the following statements is TRUE as a result of electromagnetic induction at the instant that all loops are entering the region of uniform magnetic field? A. Loops W and Y and loops X and Z will be polarized along the vertical and horizontal direction, resp. B. Loops W and Y and loops X and Z will be polarized along the horizontal and vertical direction, resp. C. All four loops will be polarized along the vertical direction D. All four loops will be polarized along the horizontal direction E. Nothing will happen 23. Apat dapat. Which loop will induce a maximum emf as they move through the field? A. Loop W v B. Loop X C. Loop Z • D. Loops W and Y • W E. Loops X and Z Y X
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24. Induction. Consider a solenoid connected to a battery. A metal ring is placed on top of the solenoid. At the instance the switch is suddenly closed, what will happen to the metal ring? A. The metal ring will jump up. B. The metal ring will not move. C. The metal ring will jump inside the solenoid. D. The metal ring will move to the right of the solenoid. E. The metal ring will move to the left of the solenoid. 25. Gummy bear. Consider a neutral gummy bear moving at a constant speed away from a conducting loop with constant current. Which is most possibly TRUE at the instant that the gummy bear begins to move away from the loop? A. The gummy bear becomes positively-charged. B. The gummy bear becomes negatively-charged. C. Positive charges accumulate at the gummy bear’s head. D. Negative charges accumulate at the gummy bear’s head. E. The distribution of charges inside the gummy bear does not change.
The SAND Prince
B