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# law (vl3748) - AC generators - mostarshed - (338) This print-out should have 23 questions. Multiple-choice questions may continue on the next column

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law (vl3748) – AC generators – mostarshed – (338) 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points A device that converts mechanical energy into electric energy is called a 1. motor. 2. coil. 3. transFormer. 4. generator. 002 10.0 points Lenz’s law is about the current induced in a loop oF wire when the magnetic ±ux through the loop changes. This induced current is always 1. in the same direction as that oF the current producing the original ±ux. 2. in a direction opposite that oF the current producing the original ±ux. 3. in such a direction as to oppose the change in the original ±ux. 4. clockwise. 5. counterclockwise. 003 10.0 points A step-up transFormer used in an automobile has a potential di²erence across the primary oF 26 V and a potential di²erence across the secondary oF 4 . 0 × 10 4 V. There are 17 turns in the primary coil. How many turns are in the secondary? Answer in units oF turns. 004 (part 1 oF 3) 10.0 points In an AC electric generator, a rigid loop oF wire rotates in an external magnetic feld. Say the loop is positioned as shown at time t = 0. A S N waterfall sliding contacts Which graph best represents the induced current i ( t ) at later times? Take i > 0 For current ±owing in direction shown by arrows. 1. i 0 v t 2. i 0 v t 3. i 0 v t 005 (part 2 oF 3) 10.0 points The AC generator consists oF N = 9 turns oF wire each oF area A = 0 . 0993 m 2 and to- tal resistance 11 . 7 Ω. The loop rotates in a magnetic feld B = 0 . 211 T at a constant Frequency oF 51 . 6 Hz. ³ind the maximum induced emF. Answer in units oF V. 006 (part 3 oF 3) 10.0 points
law (vl3748) – AC generators – mostarshed – (338) 2 What is the maximum induced current? Answer in units of a. 007 (part 1 of 2) 10.0 points A circular coil enclosing an area of 180 cm 2 is made of 220 turns of copper wire as shown in the Fgure. A 8 . 7 Ω resistor is inserted in the copper wire. Initially, a uniform magnetic Feld of magnitude 1 . 92 T points horizontally from left-to-right through the perpendicular plane of the coil. When viewed from the right the coil is wound counter-clockwise. R Magnetic ±ield B ( t ) During a 2 minute time interval the Feld uniformly changes at a constant rate, until a reversed Feld is reached equal in magnitude to the initial Feld. How much charge ²ows through the coil? Answer in units of C. 008 (part 2 of 2) 10.0 points The electrons in the resistor R shown in the Fgure 1. move left-to-right. 2. move right-to-left. 3. move in a direction that is undetermi- nated from the information given. 4. do not move in a preferred direction, since they have thermal kinetic energy. 009 10.0 points Why does a transformer require alternating voltage? 1. No speciFc reason; constant voltage would work just as well. 2. Alternating voltage leads to electromag- netic induction which is necessary for the transformer to work. 3. The magnetic Feld produced by the pri- mary coil can reach the secondary coil more easily. 4. Due to economic reasons; alternating voltage is cheaper to produce. 5. Energy can be transferred more e³ciently if alternating voltage is used. 6. If we apply a constant voltage to the primary coil, it will burn out due to a short circuit. 010 10.0 points If you took an electric motor and turned it by hand, what would happen then? 1. The motor would rotate with an constant speed even if you stop turning it. 2. There would be no current in the wires. 3. Current would ²ow in the wires. 011 10.0 points If a bar magnet is thrown into a coil of high- resistance wire, what will happen? 1. The magnet will slow down because the changing magnetic Feld will induce current in the loop, which will interact with the magnet and repel it. 2. None of these 3. The magnet will change its polarity be- cause the electromagnetic waves produced by the magnet and the coil will interact with each other. 4. The magnet will slow down and get hotter because the kinetic energy of the magnet will transfer to heat.
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