A physics problem that uses the superposition of electric fields and symmetry is in doubt, doubt, an

Field strength of a point charge: It doesn't make much sense to say that the field strength of a point charge is divergent or convergent if it is not said at which point. If point A is specified, then the field strength of the point charge is along the direction of the line between point A and the point charge (positive charge outward, negative charge inward).

The field strength of the two point charges can probably be represented by my drawing. Then the combined field strength of AD can be seen to be significantly smaller than that of BC (EA, EB, EC, ED, etc.).

4.If an equal amount of positive charge is fixed at e, then it is equivalent to having an equal amount of positive charge at all 5 corners of a regular 5-sided shape! Then the combined field strength at its center must be 0 (i.e., if there is a charge in the middle, it must be balanced).

For example, the combined field strength of the three vertices of a regular triangle must be 0There are also regular 4-sided, regular 5-sided, regular 6-sided... And so on!

The first diagram is for the second question, and the second diagram is for the third question.

<> spear is a kind of vector, that is to say, some components of the singing voice can be offset to a certain extent, to give you a hanging chart, many field strengths can be synthesized with each other, here the ABCD four points are symmetrical, the symmetry line passes through E, that is to say, the final combined field strength of the ABCD four points points to E, and the field strength of E itself points to E

<> electric field strength is a vector, and the return satisfies the parallelogram brother Minyou's rule! As shown in the envy picture!

Point A is negatively charged and point B is positively charged.

The general process of this conclusion: to a

b. Various situations of electrification.

Make assumptions. Pick out the reasonable.

Like hypothesis. Both are negatively charged, then the vector ca+

The direction of the composite vector of cb must be in ca

and CB. Another example.

A with positive and B with negative, then vector AC+

The direction of the cb and the vector must be in.

The outer corner of the ACB may be with.

AB is parallel, but it is from A direction.

B direction. And so on, only A

Negative b is positive, it will be formed.

b A direction.

The combined electric field is easy to judge according to the law of vector synthesis.

EAEB and combined field strength e

Form a right triangle. Thereinto.

EB is hypotenuse, EB with. The angle is.

degrees therefore ea=

sin60*eb

qa/ac^2

sin60qb/bc^2

qa/qbsin60

bc/ac)^2

sin60(1/sin60)^2

1/sin60=2:√3

The same field strength requires the same magnitude and direction.

To determine the direction of the field strength, just put a positive charge at that point and look at the direction of the force.

Judging from this:

The field strength of A is upward, the field strength of B is downward, the field strength of B A is in the upper right, the field strength of B is lower to the right, the field strength of C A is to the right, the field strength of B is to the right, the field strength of D A is upward, and the field strength of B is downward, only C is correct.

Answer: C First of all, we need to know that the field strength is a vector quantity, not only in magnitude but also in direction, so just judging the direction of the electric field can exclude the three options a, b, and d, where a is in the opposite direction, b is perpendicular to each other, and d is in the opposite direction.

It's easy to have different field strength directions for options a, b, and d.

You just need to know what the electric field lines look like.

College Entrance Examination Physics Hot Spots: Skillfully use "symmetry thinking" to deal with the problem of superposition of point charge field strength.

To master the methods of physical problem solving, here are a few introductions to you:

1. Isolation analysis method and integral analysis method (mechanics solves the problem of connectors).

Isolation analysis is a method of extracting selected research objects from the physical context in which they are located and conducting research and analysis. Problems that need to be analyzed by the isolation method often have several research objects, and they should be isolated and analyzed one by one. It is also necessary to find out the connections between these isolators so that they can be solved together.

To summarize the gist of this, it is as follows: first isolate the analysis, and then solve it jointly.

2. Extreme value method and end value method (the intermediate process is difficult to analyze, but the initial and final states can be known, so as to analyze the changes in the intermediate process).

Extremum problems are a common type of problem in middle school physics. In the process of changing the physical state, the change function of a certain physical quantity may not be monotonic, it may have a maximum or minimum value. There are two ways to analyze the extreme value problem:

One is to transform a physical problem into a mathematical problem, and discuss or solve the extreme value of a physical function purely from a mathematical point of view. The methods it uses are also mathematical methods such as algebra, trigonometry, geometry, etc.; The other is to find the extreme value according to the constraints and limitations of the physical laws that the object is subject to in the process of state change. The method it uses is physical analysis.

3. Equivalence method (converting multiple into one for easy analysis).

The equivalence method is an important method of physical thinking, and its main point is to transform a more complex problem into a simpler or common problem without the same effect. The key to applying the equivalence method is to be good at analyzing which problems in the problem (such as the object of study, the motion process, the state, or the circuit structure, etc.) can be equivalent.

Fourth, the micro-element method (generally used for curvilinear motion, without displacement with distance, using this method to divide it into a number of small pieces).

All macroscopic quantities can be seen as being made up of a number of tiny units. In the whole process of the motion of an object, these tiny units are an arbitrary and representative small part of the amount of time, space, and matter. Through the study of these tiny units, we can often discover the characteristics and laws of the motion of objects.

The micro-element method is a method of studying problems based on this idea.

5. Graphing method (similar to the idea of combining numbers and shapes in mathematics, images can facilitate problem solving and make the problem clear, and are generally used in kinematics).

Graphing is a method of solving problems by analyzing or solving the size and change trend of a certain physical quantity through graphing. Revealing physical processes and laws through drawing has the advantages of intuitive image, simplicity and clarity.

Hope it helps.

The electric field formula for point charge excitation is e=kq r 2p, and the electric field at the point is e=kq r1 2

The electric field at the q point is 2e=kq (l-r1) 2

Comparing the two equations, we get r1=2 (2 + root number 2).

l It's not good to play the formula here, go back and calculate Q yourself)

If you don't understand, ask me.