Name:_______________________

Test 2

05/23/2006

Ch. 20-22

Useful number(s):          m0=4p x 10-7 T m/A

1)      In the following DC circuit:

a)      (5 pts.)  Find the total resistance.

b)      (5 pts.)  Draw an equivalent circuit using the total resistance

c)      (5 pts.)  Find the average power used by each resistor.

d)      (5 pts.)  If the 12 Volt battery is replaced by 12 Volt (RMS) AC source, what is the power used by each resistor?

e)      (5 pts.)  How much energy would the battery in d) need to run the circuit for 10 hours.

Name:_______________________

2)      A 7A current flows counterclockwise in a flat circular loop of 12 turns and diameter of 10cm is shown in the figure below.  The loop can rotate about the dashed line.  A 0.022T uniform magnetic field points into the page.

a)      (5 pts.) Draw a new diagram with the magnetic field pointing to the right and the dashed line pointing out of the paper?

b)      (5 pts.) What is the net magnetic field vector at the center of the loop?

c)      (5 pts.) What is the torque on the loop about the dashed line?

d)      (5 pts.) What is the maximum torque about the dashed line?

e)      (5 pts.) How many degrees must the loop be rotated about the dashed line to achieve the maximum torque?

Name:_______________________

3)      A flat 5 turn square loop with 2m sides and a resistance of 8 Ohms is moving with a constant speed of 3m/s as shown with center at A in the figure below.  A 1.2T uniform magnetic field, which points into the page, exists only inside the rectangular region shown in the diagram.

a)       (8 pts.) What is the average current in the loop as its center moves from point A, 2m above the region containing the magnetic field to point B, 1m above?  Does the current flow clockwise or counterclockwise?

b)       (8 pts.)  What is the average current in the loop as its center moves from point B, 1m above the region containing the magnetic field to point C, directly at the top of the region?  Does the current flow clockwise or counterclockwise?

c)       (9 pts.) What is the average current in the loop as its center moves from point D, 1m above the bottom of the region containing the magnetic field to point E, right at the bottom of the region?  Does the current flow clockwise or counterclockwise?

Name:_______________________

4)      A transformer with a 40-turn primary and a 8-turn secondary has a 120Vrms AC source connected to the primary.

a)      (7 pts.) What is the rms voltage in the secondary?

b)      (7 pts.) If the transformer is 100% efficient and the primary draws 800W of power, what is the rms current in the secondary?

c)      (11 pts.) If the transformer is broken and becomes only 80% efficient how much rms current will be needed in the primary to produce 800W at the secondary?