Phy 214   Test 1    Autopsy      Spring 2005

 

1.    You have three metal blocks marked A, B, and C, sitting on insulating stands. Block A is charged "+" but blocks B and C are neutral.

 

Without using any additional equipment, and without altering the amount of charge on block A,

explain how you could make block B be charged "+" and block C be charged "-". Explain your

procedure in detail, including diagrams of the charge distributions at each step in the process.

 

 

a.  Many of your friends felt that first touching block B with block A would make it positive.  Then one could touch block C with A and it would become negatively charged.  All this without changing the charge on block A.

 

 Suppose block A initially has a net charge of + 16 C. 

 

1-1.    How much charge of what sign does it have after touching block B?

 

 

 

1-2.  Next, how much charge of what sigh would it have after touching block C?

 

 

 

 

 

 

 

b.  Others of your classmates felt that one could first hold block A near block B and that would attract the electrons from block B, causing block B to become positive.  Then one could hold block A near block C , then touch the opposite side of block C, causing causing electrons to flood onto block C from your finger so now it would be charged negatively.  All this without changing the charge on block A. 

 

1-3.  Which of these statements aer false and why?

 

 

 

 

 

1-4.  Which of these statements are true and why?

 

1-5.  Could you carry out the instructions for this problem if the blocks were plastic instead of metal?  Why or why not?

 

 

 

 

 

2.   In the diagram below, draw a vector showing the force vector on each of the charged objects caused by the other charged object.  Make the lengths of the vectors indicate the magnitude of the forces.

Being aware that opposite signed charges attract each other, suppose that the distance between the centers of the two charged objects is 3 m.

 

2-1.  Find the magnitude of the force on the -5 C charge due to the 1 C charge.

 

 

 

2-2.  Which way does it point?

 

 

 

2-3.  Find the magnitude of the force on the 1 C charge due to the -5C charge.

 

 

 

 

2-4.  Which way does it point?

 

 

 

 

2-5.  Although 7 out of 10 of your classmates will find these results very surprising (not kidding), this is an illustration of what fundamental law of physics?

 

 

 

 

2-6.  Does this result depend upon whether the objects are metal or plastic?

3.   Draw on the plastic sheet showing the polarization of the molecules in the plastic sheet caused by the charged rod.  Be very specific .

 

 

3-1                                                                 3-2. 

                                                             

 

3-3.                                                                                        3-4.  Draw the uniformly charged rod.

                                

     

4.  Find the magnitude and direction of the force on an electron located at points A, B, & C.

               

 

 

 

Use the figures below to answer the following questions.    

4-1.  If an electron were to be placed at position A, what would be the magnitude and direction of the net force acting on it due to the charged sphere?

4-2.  If an electron were to be placed at position B, what would be the magnitude and direction of the net force acting on it due to the charged sphere?

4-3 .  If an electron were to be placed at position C, what would be the magnitude and direction of the net force acting on it due to the charged sphere?

 

       

 

4-4.  If possible, draw an example of how the charge on the surface would be distributed so that the force on the electron located at A & B would not be zero.

       

Use the figures below to answer the following questions.   

4-5.  If an electron were to be placed at position A, what would be the magnitude and direction of the net force acting on it due to the charged sphere?

 

4-6.  If an electron were to be placed at position B, what would be the magnitude and direction of the net force acting on it due to the charged sphere?

 

4-7 .  If an electron were to be placed at position C, what would be the magnitude and direction of the

       

4-4.  If possible, draw an example of how the charge on the surface would be distributed so that the force on the electron located at A & B would not be zero.

5.     The charges in the diagram below are located on the corners of a rectangle whose dimensions are indicated in the figue.

 

5-1.  Find the x component of the electric field at P due to the 2C charge.

 

5-2.  Find the x component of the electric field at P due to the 3C charge.

 

5-3.  Find the x component of the electric field at P due to the-2C charge.

 

5-4.  Find the x component of the electric field at P due to the -3C charge.

 

5-5.  Find the y component of the electric field at P due to the 2C charge.

 

5-6.  Find the y component of the electric field at P due to the 3C charge.

 

5-7.  Find the y component of the electric field at P due to the-2C charge.

 

5-8.  Find the y component of the electric field at P due to the -3C charge.

 

5-9.  Find the x component of the electric field at the -3C position due to the 2C charge.

 

5-10.  Find the x component of the electric field at the -3C position due to the 3C charge.

 

5-11.  Find the x component of the electric field at the -3C position due to the-2C charge.

 

5-12.  Find the x component of the electric field at P due to the -3C charge.

 

5-13.  Find the y component of the electric force on the -3C charge due to the 2C charge.

 

5-14.  Find the y component of the electric force on the -3C position due to the 3C charge.

 

5-15.  Find the y component of the electric force on the -3C position due to the-2C charge.

 

5-16.  Find the y component of the electric field at the position of the -2C  due to the 3C charge.
6.  An electric field  of magnitude 500 N/C  is directed eastward in a particular location.  

 

6-1  Determine the magnitude and direction of  the acceleration of  an electron placed at this location.   (mass of an electron is 9x10 -31 kg, charge is 1.6x10-19C.)

 

6-2  Determine the magnitude and direction of  the force on  an electron placed at this location.   (mass of an electron is 9x10 -31 kg, charge is 1.6x10-19C.)

 

6-3.  Suppose the electron were accelerated westward at an acceleration of 3000 m/s2.  What would be the magnitude and direction of electric force acting on it ?

 

6-4.  6-3.  Suppose the electron were accelerated westward at an acceleration of 3000 m/s2.  What would be the magnitude and direction of electric field acting on it ?

 

7.  Two very thin plastic sheets are close to each other and carry equal and opposite uniform charge distributions.  Explain briefly why the field between the sheets is much larger than the field outside.  Illustrate your argument on a diagram

 

7-1.  How would the answer change if the thin sheets were of metal instead of plastic? 

 

8.  You are the captain of a spaceship. You need to measure the electric field in space in the vicinity of the spaceship.  You send a crew member outside with a meter stick, a stopwatch, and a small ball (of known mass M and net charge +Q (held by insulating strings while being carried). You must explain to the crew member what observations of the ball to make for you, and explain how you will use those observations to determine the magnitude and direction of the electric field at location P.

 

a)   Write down the instructions (in step by step form) you will give to the crew member.

 

b)   Explain how you will analyze the data that the crew member brings you, to determine the magnitude and direction of the electric field at location P.  Give the formula you will use to obtain the Electric field E in terms of the data obtained.