Exam 2 practice problems solutions

# N n s s 01 02 03 04 05 06 t 10 05 05 10 i b determine

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N N S S 0.1 0.2 0.3 0.4 0.5 0.6 t 1.0 0.5 0.5 1.0 I

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b. Determine the value of the induced current and the times during which it will be flowing. I’ll take the electromagnet, place it close to the coil, and point its north pole at the cen ter of the coil. I’ll connect the coil to the ammeter so I can measure the current that will be induced in it. The electromagnet will be off to begin with. I’ll then turn the electromagnet on. This will cause a current to be induced in the coil. The direction of the induced current will be in whatever direction is needed so that the magnetic field it creates will resist the change in the field of the electromagnet. The direction of the induced current and its magnetic field are shown in the diagram. The coil is going to act like a circuit with a single power supply and a single resistor. I can determine the current flowing in the circuit using Kirchhoff’s loop rule and Ohm’s law. This current will only be flowing during the 0.50 s that the magnetic field of the electromagnet is changing. PS W W W W w 0 0 1 V V I R I R   The electromotive force (EMF) created by the electromagnetic induction effect can be determined using Faraday’s law.     2 2 2 2 2 W w w cos cos 0 1 50 3.00 T 0.05 m 1 4.71 A 0.50 0.50 s  f i i i B i i NB A NB A NB r NB r t t t t NB r NB r I R t R t 14. You have an electron gun that creates a beam of electrons that travel with speed 7 3.00 10 m s . Your goal is to use the electromagnet described in the previous problem to make the electrons travel in a circular path (or at least part of a circle) with the smallest possible radius. a. Explain how you will arrange for this to happen. Include a labeled diagram. Be sure to show any relevant magnetic fields and clearly indicate the direction of the electron’s motion. b. Determine the radius of the circular path. To make the electrons travel in a circular path with the smallest radius I need to maximize the magnetic force being exerted on them. This happens when the velocity of the electrons makes a 90 degree angle with the direction of the magnetic field. Right hand rule #1 says that the electrons will feel a downward magnetic force at the moment they enter the magnetic field region, causing them to move in the semi-circular path shown. To determine the radius of this orbit I’ll use Newton’s 2 nd law in radial component form. 2 e on e, e e e e 31 7 5 e 19 e 1 1 sin 9.11 10 kg 3.00 10 m s 5.69 10 m 1.60 10 C 3.00 T r r q vB v a F q vB m r m m m v r q B N S mag B ind I mag B Electron gun v v v mag B
15. A parallel plate device is set up creating a uniform electric field between the plates of magnitude 7 1 10 E N C   as shown. A beam of charged particles (could be positively or negatively charged) is fired with speed v into the electric field region. You realize these particles will be deflected from traveling in a straight path by the electric field. But, you then realize that you could add a

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