Sample Exam II

Show your work!  NO Electronic communication devices

Part I:  Short Answer  (13 points each)  DO ALL THREE

1.      A generator is connected to a 2mF capacitor.  The generator produces an EMF (“Voltage”) given by (2V)cos(628t/s).  What is the RMS current through the capacitor?

 

2.       An electron (dashed line) is moving with a speed of 107m/s in a magnetic field of 0.5T, as shown at the right.  The electrons velocity makes and angle of 37o with the horizontal and B is vertically upward.)  What are the magnitude and direction of the force on the electron? 

 

 

 

3.      A proton is moving toward a wire that carries current in the direction shown. 

a)      What is the direction of the magnetic field produced at the proton by the current in the wire?

b)     What is the direction of the force on the proton?

 

 

 

Part I:  Problems  (20 points each)  DO ALL THREE

4.      A copper bar is free to slide on two conducting rail 0.8m apart.  A 10W resistor connects the two rails.  The bar is moving to the left with a speed of 5m/s.  There is a constant magnetic field into the page of magnitude 0.5T. 

a)      What is the EMF generated in the loop?

b)     What is the current through the resistor?

c)      Which direction does the current travel through the resistor?

 

5.      Both long wires (a vertical one along the y axis and a horizontal one along the x axis) in the figure at the right carry a current of 12A in the directions shown.  Find the magnetic fields they produce at two different places.  The points and the wires are all in the same x-y plane.  I suggest you calculate the field due to each wire at a particular point and then “add” them to get the total field at that point.  Be sure to indicate the direction of the net field in each case.

a)  Find the total B at A, (x=3m, y=2m).

b)  Find the total B at C, (x=3m, y=-2m).

 

 

 

 

 

6.      Three long wires are each carrying currents of 20A.  The wires at C (x=4m, y=-3m) and at the origin (O) carry current into the page.  The wire at A (x=4m, y=3m) carries current out of the page. 

a)      Find the magnitude and direction of the force on a 0.5m length of the wire at the origin exerted by each of the wires at A and C.

b)     Find the magnitude and direction of the total force on a 0.5m length of the wire at the origin. 

 

 

 

 

 

Formulas and Expressions for Exam II

g = 10m/s2  and  G = 6.67x10-11Nm2/kg2

In the figure at the right, B = C cos(J), A = C sin(J), tan(J) = A/B, and A2 + B2 = C2.

 

In the figure at the right Ax = |A|cos(J) and Ay = |A|sin(J) and A2 = (Ax)2 + (Ay)2