Download Chapter 27 The Electric Field

Chapter 27 The Electric Field
1.
The electric field of a point charge is _____________________, but realworld charged objects have vast numbers of charges arranged
___________________________.
2.
Look at figure 27.1, Notice that no matter the size or shape of the charged
object, charges seem to be evenly spaced.
3.
The electric field of a point charge is defined by formula 27.1. Write that
formula here and define all variables:
4.
Equation 27.2 ( F= Eq), tells us that the net electric field is the vector sum of
the electric field due to each charge. In other words, electric fields obey
______________________________.
5.
Looking at figure 27.3, it is clear to see that the net electric field is the result
of _______________________________________.
6.
Copy down the “Typical electric field strengths” from table 27.1. These
numbers should help you identify if the answers you get for problems in
chapter 27 are logical!!!
7.
Use example 27.1 to support the steps of the electric field of multiple point
charge strategy from page 820.
8.
Two equal but opposite charges separated by a small distance form an
___________________________.
9.
Explain the difference between a permanent and induced electric dipole:
10.
Look at figure 27.7,explain in your own words the electric dipole created on
each point charge due to the + and – charges. You may want to include sketch
and colored pencil lines to help with your explanation.
11.
It is useful to define the dipole moment shown as the variable __________.
Look at equations 27.11 and 27.12, notice the difference not only in the
numerator of these to equations. Note each equation here, define the variables
and describe under which situations each equation is used.
12.
In chapter 26 we used vectors to show “fields” at different points in space.
Now we will start using “electric field lines.” The four steps in the tactics box
on page 824 will help you draw/understand electric field lines. Copy the four
rules here:
13.
Look at figures 27.9b and 27.10, how do these sketches differ? How are they
similar?
14.
Complete the Stop and Think form page 825 here:
15.
If a charged object contains a large number of excess electrons, it is not
practical to track every electron. So…the charge is considered ____________
and ____________________.
16.
A charged rod has a linear charge density which is defined by the equation:
17.
A charged two dimensional surface has a charge density which is defined by
the equation:
18.
The equations above assume that the object is uniformly charged which means
______________________________________________________________.
19.
Complete the Stop and Think from page 825 here:
20.
Use example 27.3 to help you understand the steps in the strategy box on page
827. I suggest writing each step in the strategy with figure 27.13!!
21.
Notice in example 27.4 the equation for electric field of a rod. Copy that
formula here and define each variable:
22.
Read the section titled “An Infinite Line of Charge” and then complete the
Stop and Think 27.3 here:
23.
Complete Conceptual Questions 2 and 3 here:
24.
Complete Exercises 1,3,6,7,8 and 10 from pages 844-845 here:
25.
The electric field of a ring can be calculated just like two point charges placed
on an axis separated by a distance equal to the radius of the ring. Example
27.5 follows the five step strategy of 1) choose axis set up 2) identify the point
at which to calculate the field 3) divide the segments into segments 4)draw the
field vectors and 5) make any cancellations that are possible.
This example also clearly shows the z axis for the third dimension. Notice
that the field in the y cancels leaving only the Ez to calculate.
Complete #11 from page 845 here. Use example 27.5 to guide you.
26.
Looking at figure 27.16, explain why there is no electric field in the center of
the ring:
27.
A charged disk needs to be thought of as a series of rings which conbine to
make a solid or continuous surface.
The surface charge of a disk is described by equation 27.16. Write that
equation here and define all variables:
28.
The electric field created by a charged disk is closely related to the surface
charge through equation 27.22. Write that equation here and define each
variable:
29.
Use example 27.6 to help you complete # 13a from page 845:
30.
An electrode is a _________________________ which is used to “steer”
electrons along desired paths.
31.
Electric field strength of a charged plane is directly proportional to
___________, which means the more charge, the ______________the field.
The other important fact is that the field strength is the __________at all pints
in space around the plate independent of the distance to z.
32.
Looking at figure 27.18, a positively charged plane has an electric field on
both sides which points ___________________ from the plate. If the plate
where negatively charged, the field lines would _______________________
on both sides of the plate.
33.
A sphere charge distribution can be compared to gravitation fields of planets!!
It will not matter if the object is a hollow or solid sphere, as long s the charge
distribution is uniform. The electric field created by a sphere is calculated via
equation 27.28. Write that equation here and define each variable:
34.
Complete the Stop and Think on page 833 here:
35.
A capacitor is made of ________ electrodes placed a distance apart. These
plates are so equally but _______________ and known as a
_________________________.
36.
The net charge of the capacitor is ____________ and charged by transferring
electrons from one plate to the other. Because opposite charges attract, all of
the charge is on the ____________ surfaces of the two plates and can be
modeled as charged planes with opposite surface charge densities.
37.
Inside the capacitor the field points from the _____________ plate to the
_______________plate. BUT outside of the capacitor the field is 0. Explain
in your own words why this happens:
38.
The electric field within the capacitor can be defined by equation 27.29.
Write both variations of this equation and define each variable:
39.
What is a fringe field?
40.
Does the shape of the electrodes matter? Explain your response:
41.
Read the section on “uniform electric fields” and then complete the Stop and
Think 27.5 from page 835.
42.
Now it is time to define the motion of a charged particle in an electric field
calculated through the equation F=qE. Notice in figure 27.24 that if a proton
is placed in the electric field it moves ______________________ but an
electron placed in the electric field moves
____________________________________.
43.
If F is the only force action on the charged particle, the particle can accelerate
due to Newton’s ____________ Law. Acceleration can be defined as force
divided by mass OR (charge times electric field) divided by mass.
44.
Will a proton and a sodium ion experience the same acceleration when placed
in an electric field? Explain:
45.
A charged particle in a uniform electric field will move with constant
________________________ but the direction of motion must be determined.
46.
What are some uses for particle acceleration between capacitor gaps?
47.
The force created by an electric force is (qE) OR charge times electric field
force. Remember from objects in circular motion that F= mv2/r. So looking
at figure 27.27, an electron moving in a circular path around a proton is driven
by the force of attraction.
qE= mv2/r
48.
Complete the Stop and Think from page 838 here:
49.
In a uniform electric field the net force on a dipole is ___________________.
Also, the electric field will cause the dipole to rotate until the net torque is
_____________________________ and the dipole is at its equilibrium
position. According to figure 27.28b, the ______________ end of the dipole
points in the direction of the electric field.
50.
As a dipole turns into its equilibrium position it will “feel” torque forces.
Torque is defined by the angle which it turns through as it moves into its
equilibrium position. Torque is defined in several terms via equations 27.34
and 27.35…but notice these are basic trig relations.
51.
If a dipole is placed by a point charge, such as in figure 27.32, the net force is
toward the strongest area of the field…where the lines are closest together.
The dipole will just “flip” so that it will move into that part of the field.
52.
Complete the following exercises from pages 845-847 here: #17,19,21,22,25
and 27.