S2005-Final

# S2005-Final - PHYSICS 112 - FINAL EXAM (second,...

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PHYSICS 112 - FINAL EXAM (second, comprehensive part) - SPRING 2005 cos 0° 1 cos 30° 0.75 cos 45° 0.50 cos 60° 0.25 cos 90° 0. 2 222 2 œ œœœ œ 1. [9 points total] An electric charge of 2.0 C is placed at a point 3.0 m from a fixed . electric charge of 3.0 , and then released from rest at time 0. G > œ . (a) [1 point] Is the force between them repulsive or attractive? (b) [2 points] What is the magnitude of that force at the beginning? (c) [1 point] How does the force change with time? (d) [3 points] Make a rough plot of how the speed of the moving charge changes with time. Indicate whether or not there is any limit to how large or small the speed becomes. Speed 0 m/s >p∞ 0 (e) [2 points] After a long time, what will be the kinetic energy (in J) of the moving charge?

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2. [4 points total] (a) Suppose that the electric field at a certain point is I t œ (1000 N/C, 500 N/C). What is the electric force produced by that field on a charge of 20 C? . (b) At a different point in space a 20 C charge experiences an electrical force . 3. [6 points total] A 15-V battery is connected in series to a 3-ohm resistor and a 2-ohm resistor. (a) [2 points] What is the current through the 3-ohm resistor? (b) [2 points] What is the power dissipated by the 2-ohm resistor? (c) [2 points] What is the total power delivered by the battery?
4. [9 points total] A square metal loop whose sides are each 0.20 m long is placed in a uniform external magnetic field F t of magnitude 2.0 T, as shown in the diagram. Initially there is no current in the loop. The loop has an electrical resistance of 5.0 . H F t Æ (a) [3 points] Over a period of 4.0 seconds the external magnetic field is rotated from its initial position (shown) until it is straight up . Determine the magnetic flux through ÐÑ the loop at the beginning and end of this rotation. F initial œ ___________________________________________ F final œ ___________________________________________ (b) [2 points] Determine the magnitude of the average induced current. (c) [2 points] Determine the direction ( , , , , , or ) of the induced ÅÄÃÆ Œ magnetic field of the loop and the direction of the induced current (clockwise or counterclockwise). Explain your reasoning. (d) [2 points] Suppose the external magnetic field did not change its direction, but that there was a clockwise current in the loop (from a battery in its circuit, say). Would there be a net torque on the loop and, if so, how would it rotate?

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5. [8 points] An object 4.0 mm high is located on the principal axis of a divergent lens whose focal points are located 12.0 cm from the lens.
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## This note was uploaded on 02/11/2012 for the course PHYSICS 112 taught by Professor Fretwell during the Summer '08 term at Iowa State.

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S2005-Final - PHYSICS 112 - FINAL EXAM (second,...

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