Practice Exam 3

INSTRUCTIONS: Complete the following as indicated. Be sure to show your reasoning, your starting equation and units on your final results. If you need clarification on a problem, raise your hand, and I'll try to help you understand the question. Good Luck.

Electron mass = 9.11x10^-31 kg      m_o = 4 p x 10^-7 N/A²

1.  Describe the physics behind the demonstration involving the aluminum pipe/tube and the two cylinders, one which was magnitized and the other which was not magnetized.

2.  In what direction must the magnet be moving in order to generate the indicated current in the conducting ring? Explain.

3.  A loop moves with constant velocity (from left to right) through a region where uniform magnetic field is directed into the plane of the page, as indicated below.   Indicate the regions where positive charge and negative charge accumulate. 

6.  The Bohr model of hydrogen has the electron circulating around the positive nucleus with a speed of 2.2x10⁶ m/s and at a radius of 0.0529x10^-9 m.

a. What is the effective current of the electron? (Hint, I is charge passing a point per second so you should be able to use Q and T to come up with I, where T is the period of the revolution)

b. What is the magnitude of the magnetic field due to this current at the nucleus (i.e. at the center of the orbit)?

7.  A coil consists of 300 turns of wire of area 4x10^-3 m² oriented perpendicular to a uniform magnetic field of 0.230 T. The loop is compressed so that its area is reduced to 1.7x10^-3 m² in a time of 19 ms. What is the average EMF generated by the coil during this time?

9.  The earth's south geographic pole is a _________________ magnetic pole.

10.  For a straight wire carrying a current, the direction of the ___________________ is given by the _______________ _______________ rule with the fingers in the direction of the _______________________________.  Household electric circuits have ____________________ recepticals with a short and long stotted opening.  The ______________ wire carries current and has the sinusoidally varying voltage, where as the _________________ also carries current but is always at zero potential with respect to ground. 

11.  Two motors are connected to the SAME household circuit breaker circuit (i.e. in parallel).  They each draw electrical energy at the rate of 1 kilowatt.  If the circuit breaker is 15A, does it stay closed?

15.  Currents of 200 and 500A flow into the page as shown in the figure below. 4.00m separate the two parallel wires. Determine the magnetic field (both magnitude and direction) at the point, P, located 4.00 m up the y-axis.

16.  Consider only the two current carrying wires in the previous problem. What is the magnitude and direciton force on the right wire if they are both 3 m long?

17.  A coil carries a clockwise current of 2 A in a single turn loop with enclosed area 1.25 m² and is rotated 30 deg away from the area vector being aligned with the magnetic field.  What is the magnitude of the torque on the loop?  How many degrees does the loop need to rotate to be at stable equilibrium (there is also an unstable equilibrium angle)?

19. What is the equivalent capacitance of the following circuit? All capacitances are in mF.