Exam 3 cont 3 of 10 0 Ensure that you have printed your full name and student ID number with clear and neat handwriting on both the front page of this exam AND on your bubble sheet Your student ID number is not written on your BuffOne Card Bubble in version A on your bubble sheet Failure to follow these instructions may result in the loss of one point on this exam 1 A solenoid is constructed with a wire wrapped into N turns of radius R spanning a total length L The magnetic eld inside has magnitude B0 when the current through the solenoid is I0 Another solenoid is constructed with 2N turns of a radius R also spanning a total length L If a current I0 is passed through this new solenoid what will be the magnitude of the magnetic eld inside it Assume both solenoids are long enough compared to their radius that the in nite solenoid approximation is valid A B0 4B0 2B0 D B C B0 2 E B0 4 2 An 0 500 F capacitor a 400 ohm resistor and a switch are connected in series The switch is open and the capacitor is initially charged with a charge Q0 2 00 C At time t 0 the switch is closed At what time t is charge on the capacitor equal to 5 00 of its initial value A B C D E There is no current 3 00 s 200 s 599 s 500 s 3 A wire carrying a constant current I sits near a bar magnet as shown The wire and the magnet lie in the same plane What is the direction of the magnetic force on the wire due to the bar magnet A B C D E A B C D E Into the page Out of the page Up Down There is no magnetic force on the wire 4 A conducting metal ring of area A 0 0100 m2 spins around the ver tical axis at a frequency of f 10 0 Hz that is 10 0 rotations per sec ond There a uniform horizontal magnetic eld into the page with a magnitude of B 1 00 10 4 T which is about the size of the Earth s eld What is the maximum emf induced in the ring as it rotates No EMF is induced 2 10 5 V 2 10 3 V 1 00 10 5 V 1 00 10 6 V Version A Exam 3 cont 4 of 10 The next two questions refer to the situation below A particle of charge q and mass m moves in a region of space where there is a uniform magnetic eld of magnitude B in the z direction out of the page 5 At the instant shown a particle is moving in the x direction If q is negative what is the direction of the force on the particle due to the magnetic eld at the instant shown A y B y C z D z E There is no force on the particle 6 Suppose that you add an electric eld to the region so that the negative particle will travel in a straight line if it has a speed v What magnitude of electric eld is required There is no E eld that will allow it to travel unde ected qvB vB vB q A B C D E mv qB 7 Two long straight wires each carry current I as shown below They intersect the y axis a distance d above and below the origin as shown What is the net magnetic eld due to the two wires at Point P which is on the x axis a distance d from the origin A B C D E 0I 2 d 0I 2 d 0I p2 d 0I p2 d 0I d upward to the right to the right upward upward Version A Exam 3 cont 5 of 10 8 Consider the circuit at the right The light bulbs are identical and the battery is ideal Initially the switch is closed for a long time Then the switch is then reopened Describe the behavior of bulb A and bulb B from just after the switch is opened to a long time later A B C D E Both bulbs initially glow equally brightly and then gradually become dark Neither bulb will glow after the switch is opened Only Bulb B will glow and it will maintain con stant brightness Only Bulb A will glow and it will maintain con stant brightness Only Bulb A will glow and it will glow brightly initially and then gradually become dark into the page A B C D E There is no magnetic force on the wire 9 Three long straight wires each carry a current Io as shown in the gure What is the direction of the magnetic force if any on the wire shown at point P 10 Consider the pair of long parallel wires with equal currents shown below Arrows give the direction of the current in each wire In which of the regions is there a place where the elds exactly cancel so that the net magnetic eld is zero Don t consider distances very far from the wires where the eld goes to zero A B C D E Region I only Region II only Region III only Regions I and III None of the regions Version A Exam 3 cont 6 of 10 11 A square loop is rotating in a constant external magnetic eld out of the page At the instant shown the loop is out of the plane of the page with left side of the loop above the page and coming out of the page the right side in going in The direction of the induced current is A B C A B No induced current 12 An electron of mass me charge e and speed v moves in a circular orbit of radius R in a region of uniform magnetic eld B near the Earth s North Pole The electron then collides with another electron causing its speed to double to 2v The direction of the electron s velocity is unchanged during the collision What is the new radius of its orbit A R E 4 C R R 2 4R 2R D B 13 Consider the following con guration of B eld lines solid lines and the imaginary square loop dotted line Which one of the following statements must true about the electrical current in the loop A B There must be no net current going through the loop There must be a non zero current through the loop coming out of the page There must be a non zero current through the loop going into the page There must be a non zero current going clockwise around the loop There must be a non zero current going counter clockwise around the loop C D E 14 A long straight horizontal wire carries a current to the right At a particular instant a particle with charge q is directly below the wire moving into the page as …
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