Physics 224 Fall 00

Final Exam Dec 12

Name_________________________

 

Good luck!  Please show all work since this will be graded with partial credit.

 

Problem

Points

Score

Prob

Pts

Score

 

 

1

10

 

9

15

 

Test 1

 

2

30

 

10

10

 

Test 2

 

3

10

 

11

10

 

Test 3

 

4

10

 

12

15

 

Test 4

 

5

15

 

13

15

 

HW/Q

 

6

10

 

14

10

 

Final

 

7

10

 

15

10

 

Total

 

8

10

 

16

10

 

%

 

 

 

 

Total

200

 

Grade

 

 

Note: Homework scores were only used if they helped the final grade.  They were not used if they lowered the grade.

 

                   

 

(or F/m)                    

 

             

                              

                     DV = Ed  DU = qDV                  

V = (kQ)/R             C = Q/V  U = (kqQ)/r                                      V = IR                    

                                                          

                                              

            Tm/A                                            

 

 

 

 

1.(10pts) The force between two positive point charges is 40N.  If the charges are separated

by a distance of 15 cm and one of the charges is 6 mC, what is the other charge?

 

 

 

 

 

 

2.(3pts each) Circle T for True, F for False.

 

a)  T     F          Charge cannot be present on an insulating material.

 

b)                     When a current is present in a solenoid the magnetic field is found

                        on the ____________ of the solenoid.

 

c)  T     F          The net charge on a conductor is distributed on the surface of the conducting material.

 

d)                     Current is defined to be the _______ ___ __________ of the charge that flows.

 

e)                     If an electron is traveling from left to right across this page and a magnetic field

                        is projecting directly out from the page, the force acting on the electron would

                        point straight _________________.

 

f)                      V = IR is the mathematical expression for _______________ law.

 

g)  T     F          The force exerted by two parallel current carrying wires is repulsive if the currents

                        are in opposite directions.

 

h)  T     F          Lenz’s Law states that the effect of the induced emf is such as to oppose the change

                        in flux that produces it.

 

i)  T      F          Magnetic field lines start on the North pole and end on the South pole.

 

j)                      Flux entering a closed surface is (circle one):   Positive               Negative

 

 

 

3. (10pts)                             Find the sign (+/-) for

  DV       DU      DK

            B·        A·

                               E               a) A positive charge is moved from B to A

            C·                               b) A negative charge is moved from B to A

                                                c) A negative charge is moved from C to B

                                                d) A positive charge is moved from A to C

 

 

 

4.(10pts)  A non-conducting uniformly charged sphere of radius .02 meters has a total charge of

10 mC distributed throughout its volume.  Find the Electric field strength at a distance of .8 meters

from the center of the sphere.

 

 

 

 

 

 

 

 

 

5.(15pts) A point charge of 5 mC is placed at the point (2, 2) and a point charge of –5 mC is placed

at the point (2, 0).  Find the electric field strength on a point charge placed at the point (0, 1).  All

distances are meters.

 

 

 

 

 

 

 

 

 

 

 

 

 

6.(10pts) Find the potential  midway between  two point charges of 8 mC, and 10 mC, if they are

separated by a distance of 2 cm.

 

 

 

 

 

 

 

 

 

 

7.(10pts) When 9V is applied across a wire of length 1 meter and radius .1cm, a current of .5 Amps

flows through the wire.  Find the resistivity of the wire.

 

 

 

 

 

 

 

 

 

 

8.(10pts)  The equivalent capacitance of the figure is 10mF.  What is C?

 

 

 

 

 

 

 

 

 

 

9. (15pts)  A capacitor is charged to its maximum amount and then discharged.  Find the time elapsed when the charge on the capacitor is the same when both charging and discharging.

 

 

 

 

 

 

 

 

 

 

 

10.(10pts) A proton has a velocity of  m/s in a magnetic field  G.  Find the

force exerted on the proton.

 

 

 

 

 

 

 

11.(15pts) Four long, straight wires are at the corners of a square with sides of 20 cm as in the diagram.

Find the resultant magnetic field at the center of the square.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12. (15pts)  In a mass spectrometer, charged particles enter a chamber with an electric field and

a magnetic field present.  Explain how the particles are sorted so those only with velocity

equal to E/B will leave the chamber.  (examine the forces on the particles and the orientation

of the fields. also, it is ok to draw a diagram)

 

 

 

 

 

 

 

 

 

 

 

13. (10pts)  A parallel plate capacitor has a capacitance of 10 mF.  How could you change the

geometry of the capacitor to double the capacitance?

 

 

 

 

 

 

 

 

 

14.(10pts)  A square area of side 10 cm is set at a 30 degree angle to a uniform magnetic field of

.4 Tesla.  Find the magnetic flux through the area.

 

 

 

 

 

 

 

 

 

 

 

 

15.(10pts)  Use the diagram to explain the direction the current will flow as the magnet

recedes from the loop. (invoking someone’s law would be nice.)

 

 

 

 

 

 

 

 

 

 

 

16.(10pts)  Three ideal batteries are connected in series with two resistors as in the diagram.  Find the

current in the circuit.