EXAM 2  Practice Problems
 

USEFUL CONSTANTS:  q (electron) = -1.6 x 10-19 C

5]     A small night light operates with a current of 50 milliamps. If the light is turned on for 8.0
        hours, how much charge moved through the filament?

        Answer: 1.4 x 103 C
 

6]     The filament of an automobile parking light bulb develops 25 watts of power when connected
        to the car’s 12 V battery. What is the resistance of the filament when operated under these
        conditions?  Would the resistance of the filament be the same when the bulb is disconnected
         (no current flowing through it)?

        Answer: 5.7 W , NO
 

1] Find the currents I1 , I2 , and I3 for the circuit shown below

ANSWER:   I1 = +1.0 A ,   I2 = -1.0 A ,    I3 = 0.0 A

2] Find the equivalent resistance between points a and b for the resistor combination shown below.
     All resistors have a value of 1.0 Ohm.


ANSWER:   R equivalent =  1.6 Ohm   or  8/5  Ohm
 
 

8]     The filament of an automobile parking light bulb develops 25 watts of power when
           connected to the car’s 12 V battery. If the filament is made of tungsten wire
            (r = 5.6 x 10-8 W m) with a cross sectional area of 3.2 x 10-7 m2 , how long is the wire?
                (remember, there are lots of little coils in filaments)

        Answer: 33 meters
 


Multiple Choice Examples

1.  Kirchoff's junction rule is really just a statement reflecting the principle of

       a)  conservation of electricity
       b) conservation of mass
       c) conservation of charge
       d) conservation of energy
       e)  conservation of momentum

2.   The length of a wire is doubled and the radius is doubled.  By what factor does the resistance change?
       a.  4 times as large
       b.  twice as large
       c.  unchanged
       d.  half as large
       e.  one quarter as large

Answers:

1.  c
2.  d