Exam 2 -- Fall 2005 solutions

Exam 2 -- Fall 2005 solutions - Physics 240 Fall 2005: Exam...

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Unformatted text preview: Physics 240 Fall 2005: Exam #2 Solutions Please print your name:___________________________________________________ Please list your discussion section number:___________________________________ Please list your discussion instructor:________________________________________ Form #1 Instructions 1. Fill in your name above 2. This will be a 1.5 hour, closed book exam. The exam includes 20 questions. 3. You may use a calculator, please do not share calculators 4. You may use two 3x5 note cards (one from the first exam, plus one new one) with notes and equations you think may be useful. You can write on both sides of the card if you like. 5. You will be asked to show your University student ID card when you turn in your exam. ID checked by:___________________________________ Table of constants: = 8.85 x 10-12 C 2 /Nm 2 k = 1/(4 ) q electron =-1.6 x 10-19 C q proton =1.6 x 10-19 C m electron =9.1 x 10-31 kg m proton =1.67 x 10-27 kg = 4 x 10-7 Tm/A G = 6.67 x 10-11 Nm 2 /kg 2 1: An electron moving with a velocity of 525 m/s in the x direction enters a region filled with a constant magnetic field. The magnitude of this field is 0.5 Tesla, and it points into the page. This constant field region is 3 m long and 1.5 m wide. The electron enters 20 cm from the top of the region. What is the magnitude of the electrons velocity when it leaves the region? a) 367 m/s b) 692 m/s c) 560 m/s d) 920 m/s e) *525 m/s 2: Two long, straight wires are perpendicular to the plane of the paper as shown in the drawing. Each wire carries a current of magnitude I. The currents are directed out of the paper toward you. Which one of the following expressions correctly gives the magnitude of the total magnetic field at the origin of the x, y coordinate system? d I e d I d d I c d I b d I a 2 ) ) 2 ) 2 ) 2 ) Because the magnetic force is always perpendicular to the direction of motion, it can never do work on the particle, and its kinetic energy (and hence speed) never changes. So it leaves the region with the speed it entered with. Each of the wires will create a magnetic field with magnitude: B = I/2 d The wire on the x axis will produce this field in the y direction, the wire on the y axis will produce this field in the +x direction. To get the total magnitude, I have to find the magnitude of the vector with these two components: B total = (B x 2 + B y 2 ) = (( I/2 d) 2 + ( I/2 d) 2 ) = 2* I/2 d B total = I/( 2) d 3: Two loops carry equal currents I in opposite directions. The loops are held parallel, in the positions shown in the figure, and are then released. Which one of the following statements correctly describes the subsequent behavior of the loops? You may ignore any possible effects of gravity....
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Exam 2 -- Fall 2005 solutions - Physics 240 Fall 2005: Exam...

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