PH 1120                                                                                                                                                          Term B, 1997
STUDY GUIDE 1

1. What are study guides?

They are handouts that provide you with information indicating what is expected of you to pass the course and serve as an aid in using the textbook. 2. What is in them? The guides contain statements of the objectives around which the course is designed. They point to particularly important sections of the text. They single out especially valuable examples worked out in the text. They list problems that you should attempt in order to see if you satisfy the objectives of the course. 3. What are the objectives? They are statements indicating what we think you should be able to do to demonstrate that you have learned the material. 4. Are the study guides useful? If you use them, yes. They will help you pass the course and learn some physics. If you don't use them, they are of no use! Objective 1 State Coulomb's law. (This means write it out in symbolic form and make sure you can define each symbol used in the expression.)

Given a set of point charges (two or more) at rest at specified locations, calculate the resultant force (vector quantity) on one of the charges caused by the other charge(s).

 ALL VECTOR QUANTITIES MUST BE EXPRESSED EITHER IN COMPONENT FORM
( i,j,k NOTATION) OR IN TERMS OF A MAGNITUDE AND AN ORIENTATION RELATIVE TO WELL DESIGNATED COORDINATE AXES.

Suggested Study Procedures

Read Secs. 22-1 through 22-4. Study carefully Sec. 22-5. KNOW WHAT THE PRINCIPLE OF SUPERPOSITION MEANS AND HOW TO APPLY IT TO SOLVE PROBLEMS. Examples 22-1 through 22-4 are particularly important. Make sure you can solve problems similar to Example 22-4. Suggested Exercises and Problems Related to Objective 1:

Do this one first. Determine the unit vector directed

Objective 2 Suggested Study Procedures Study Secs. 22-6 and 22-7 paying particular attention to examples 22-5 through 22-9. You should examine Examples 22-10, 22-11, and 22-12 as we will refer to them later in the course. Suggested Exercises and Problems Related to Objective 2 Objective 3

Sketch qualitatively the electric field lines associated with: (see the rules below).

Suggested Study Procedures

Study Sec. 22-8.

One difficulty faced by students of electricity is that the electric field seems so abstract or ethereal; there's nothing solid to help get an idea of what is going on. Electric field lines form a useful way to picture how the electric field behaves in space. Rules for drawing electric field lines: 1. Field lines begin and end only on charges.
2. The number of lines beginning at a positive charge or ending at a negative charge is proportional to the charge.
3. At each point along a field line the direction of the field line is parallel to the direction of the force experienced by a small positive test charge placed at that point.
4. The density of field lines (the number of lines passing through an area of one square meter whose surface is perpendicular to the lines) is proportional to the magnitude of the field.
5. No two field lines can cross.
6. Under electrostatic conditions, field lines always meet the surface of a conductor perpendicularly; under electrostatic conditions no field lines penetrate a conductor. Suggested Problem Related to Objective 3

Sketch electric field line diagrams for each of the following configurations:

a) · +q                                                                   b) · -q

 

· -2q                                                                                                                     · 3q

 
                                                                -q
 
 

 

c) d)

Homework assignments

The homework assignments are an important part of the course and overall will count as 10% of your grade. While there will be no attempt to keep students from working with each other, blatant copying of the work of another will only lead to a sense of false security on examination work.

There will be an attempt to make the homework problems as realistic as possible, so you are encouraged to view them as something more than exercises to answer.

PLEASE NOTE THAT HOMEWORK SOLUTIONS WILL ONLY BE ACCEPTED IN LECTURE! ON THE DUE DATE.

 HOMEWORK ASSIGNMENTS FOR STUDY GUIDE 1

Homework Assignment #1 - due in lecture Friday, Oct. 31

A small charge of 5 x 10 -6 C is located at the point x = 2 m, y = 2 m in the x-y plane. A second small charge of - 3 x 10 -6 C is at the point x = 5 m, y = -2 m.

a) Draw a diagram showing the two point charges in the x-y plane.

b) Calculate the force that the first charge exerts on the second. Remember: FORCE IS A VECTOR so you must give a magnitude and direction or express your answer in vector notation (specifying the i and j directions).

c) Calculate the force that the second charge exerts on the first charge.

Suppose the second charge was moved from (x = 5m, y = -2m) to the point (x = 5m, y = 2m). Without detailed calculation, answer the following:

d) Would the magnitude of the force on the second charge be larger than, smaller than, or the same as before it was moved?

e) Would the direction of the force be the same or different?

 Homework Assignment #2 - due in lecture Monday, Nov. 3

For the problem in Homework #1:

c) Suppose the –2 x 10 –6 C charge at the origin is replaced by a +2 x 10 –6 C charge. Is the magnitude of the force on the +2 x 10 –6 C charge larger than, smaller than, or the same as it was on the –2 x 10 –6 C charge? Homework Assignment #3 - due in lecture Wednesday, Nov. 5 Homework Assignment #4 - due in lecture Friday, Nov. 7