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# 23-2b - brown(twb493 Ch23 h2b chiu(56565 This print-out...

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brown (twb493) – Ch23 h2b – chiu – (56565) 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points A coil is suspended around an axis which is co-linear with the axis of a bar magnet. The coil is connected to a resistor with ends la- beled a and b . The bar magnet moves from left to right with North and South poles la- beled in the figure. Use Lenz’s law to answer the following ques- tion concerning the direction of induced cur- rents and magnetic fields. R a b v S N What is the direction of the induced ma- gentic field in the coil and the direction of the induced current in the resistor R when the bar magnet is moving left to right? 1. The induced magnetic field is zero and the induced current is zero. 2. The induced magnetic field is left to right ( B induced = ) and the induced current is zero. 3. The induced magnetic field is zero and the induced current flows from a through R to b ( I −→ ). 4. The induced magnetic field is left to right ( B induced = ) and the induced current flows from a through R to b ( I −→ ). 5. The induced magnetic field is right to left ( = B induced ) and the induced current is zero. 6. The induced magnetic field is left to right ( B induced = ) and the induced current flows from b through R to a ( ←− I ). correct 7. The induced magnetic field is zero and the induced current flows from b through R to a ( ←− I ). 8. The induced magnetic field is right to left ( = B induced ) and the induced current flows from b through R to a ( ←− I ). 9. The induced magnetic field is right to left ( = B induced ) and the induced current flows from a through R to b ( I −→ ). Explanation: The induced magnetic field depends on whether the flux is increasing or decreasing. The magnetic flux through the coil is from left to right. When the magnet moves from left to right, the magnetic flux through the coils decreases. The induced current in the coil must pro- duce an induced magnetic field from right to left ( = B induced ) to resist any change of magnetic flux in the coil (Lenz’s Law). The helical coil when viewed from the bar magnet winds around the solenoid from ter- minal b clockwise. Since the induced field is right to left ( = B induced ), the induced current flows from b through R to a ( ←− I ); i.e. , counter- clockwise. 002(part1of2)10.0points A circular coil enclosing an area of 118 cm 2 is made of 110 turns of copper wire as shown in the figure. A 7 . 8 Ω resistor is inserted in the copper wire. Initially, a uniform magnetic field of magnitude 2 . 71 T points horizontally from left-to-right through the perpendicular plane of the coil.

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23-2b - brown(twb493 Ch23 h2b chiu(56565 This print-out...

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