exam2_solutions

# exam2_solutions - 1 A circular coil lies flat on a...

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Unformatted text preview: 1. A circular coil lies flat on a horizontal table. A bar magnet is held above its center with its north pole pointing down. The magnet is fixed and does not move. It induces (when viewed from above) A) a clockwise current in the coil. B) a counterclockwise current in the coil. C) no current in the coil. D) a current whose direction cannot be determined from the information given. E) alternating current. Solution: Faraday’s law: t ∆ ∆Φ- = B ε . Magnet is stationary – flax is not changing – emf is zero – no current in the coil. 2. A uniform magnetic field B is perpendicular to the area bounded by the U shaped conductor and a movable metal rod of length l. The rod is pushed along the U shaped conductor at a speed v . The total resistance of the loop is R . What is power needed to move the rod? A ) = 2 2 2 B l v P R B) R v Bl P 2 2 = C) R lv B P 2 2 = D) R v l B P 2 2 = E) R Blv P = Solution: P Find R v l B Given : , , , : R v l B R R Blv R I P R v l B Fv P R v l B lB R Blv IlB F R Blv R I Blv dis ext 2 2 2 2 2 2 2 2 2 2 = = = = = = = = = = = ε ε B v l B v l 3. The coil of a generator has 50 loops, each with a cross-sectional area of 0.25 m 2 . What is the maximum emf generated by this generator if it is spinning with an angular velocity of 4.0 rad/s in a 2.0 T magnetic field? A) 20 V B) 40 V C) 60 V D) 80 V E) 100 V Solution: ( 29 ( 29 ( 29 V s rad m T NBA N N 100 / . 4 25 . . 2 50 2 max 1 max = = = = ϖ ε ε 4. The loop of wire is being moved to the right at constant velocity. A constant current I flows in the long straight wire in the direction shown. What statement is correct about the current induced in the loop? A) It is directed clockwise and is proportional to I B) It is directed counterclockwise and is proportional to I C) It is directed clockwise and is proportional to I 2 D) It is directed counterclockwise and is proportional to I 2 E) It is zero Solution: The direction of the induced current is clockwise and it is proportional to I. 5. The drawing shows the uniform magnetic field inside a long, straight solenoid. The field is directed into the plane of the drawing, and is increasing. What is the direction of the electric force on a positive point charge placed at point a ? A) To the left B) To the right C) Straight up D) Straight down E) The electric force at this point is zero Solution: To the left 6. An electric field can be produced by a A) changing magnetic field B) constant magnetic field C) either a constant or a changing magnetic field D) changing gravitational field E) none of the given answers Solution: ∫ ∫- = A d B dt d l d E . An electric field can be produced by a changing magnetic field....
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## This note was uploaded on 02/11/2012 for the course PHYSICS 222 taught by Professor Ogilvie during the Fall '05 term at Iowa State.

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exam2_solutions - 1 A circular coil lies flat on a...

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