A topic of physical electrostatic field in the first year of high school, a topic of physical electr

Consider the extreme cases:

The distance between the tentative charge and the positive charge on the left (or the negative charge on the right) is very small. The electric field must be too large, and the electrostatic force is also very large. Certainly bigger than the r 2 place.

Therefore, it is not right to say that the field is strong and the force is the largest. If it's a fill-in-the-blank multiple-choice question, write the minimum directly, but if it's a question and answer question, you have to prove it a little.

Proofing 1: Column equations.

Assuming that the distance between the tentative charge and the + charge is x, then the distance between it and the - charge is (r-x), and the combined field strength is kqq x +kqq (r-x), which can be found properly with two uniform inequalities and is the smallest only when x=r 2.

Method 2: Symmetry (this amount of thinking is relatively large).

Assuming that the middle field strength is not the smallest, then the field strength on the middle side is smaller than the middle field strength, and the field strength on the charge side is definitely very large, so the electric field strength will have at least 3 stations, which is impossible for the electric field strength that only contains 2 relationships. So the middle field strength is minimal.

The field strength is the smallest at this point in the straight line where the two charges are connected.

The field strength is greatest at this point over r 2 and perpendicular to the straight line.

And the electric field force is not only related to the field strength, but also to the magnitude of the charge in the electric field.

Therefore, the magnitude of the electric field force cannot be judged.

The equation in your problem, mechanical energy = kinetic energy + gravitational potential energy, uses conservation of mechanical energy.

The premise that conservation of mechanical energy is used is that no work is done by forces other than gravity.

In this problem, friction does the work, so the law of conservation of mechanical energy is not satisfied. Because a part of the energy is consumed by the work done by friction.

With conservation of mechanical energy, it is important to keep this premise in mind, this is an area where it is easy to make mistakes, and it is also where exams are often examined.

Friction produces internal energy, which is not mechanical energy.

The prerequisite for the conservation of mechanical energy is that only the work is done by gravity, there is f here, do you forget to bring f in, it should be the initial movement + initial potential = the last movement + the final potential + frictional force to do the work.

Because there's friction ... Energy is also consumed.

Apparently the ball is positively charged, which is obtained by the equilibrium condition

mgtan 37°＝eq①

Therefore e 3mg4q

2) After the direction of the electric field changes downward, the ball begins to swing in a circular motion, and the force of gravity and the electric field do positive work on the ball by the kinetic energy theorem:

mg qe)l(1 cos 37°) 12mv2 is known by circular motion, at the lowest point, f to ft(mg qe) mv2l

Coupling of the above formulas, the solution: ft 4920mg

Answer: (1) 3mg4q (2) 4920mg do not understand the question.

To require the strength of the electric field, the magnitude of the electric field force is required, and the force analysis of the ball in the shown state is carried out. The ball is subjected to a vertical downward gravitational force, a horizontal rightward electric field force (only horizontally to the right), and a rope pull diagonally to the upper left. The tension is broken down vertically and horizontally.

Because the force of the ball is balanced, it can be obtained: tensile force * cos37 = g, tensile force * sin37 = electric field force. The magnitude of the electric field force can be found, and then the electric field strength can be found.

When the direction of the electric field changes, the process of the ball falling to the lowest point is a circular motion, which requires the rope to pull force, and it is necessary to know the velocity of the ball at the lowest point. According to the conservation of energy, in this process, the electric field force and gravity do positive work, so the electric potential energy and gravitational potential energy are converted into kinetic energy. The kinetic energy obtained can be found from the conservation of energy, and the velocity at the lowest point can be obtained from the kinetic energy theorem.

The tension of the rope can then be found from the centripetal force formula.

Question 1: Analyze the force of the ball, a vertical downward gravity, a horizontal to the right electric field force, and a pulling force along the rope upward. The resultant force of the three forces is zero.

It can be obtained: f electricity = g*tan37. And because f = eq, g*tan37=eq, you can find e.

The second question: From the above question, it can be seen that the physical charge is positive. The direction of the electric field changes, using the kinetic energy theorem. From this point to the lowest point, w = ek2-ek1

Ek1=0, gravity, electric field force both do work, mg*(l-l*cos37)+eq*(l-l*cos37)=1 2mv(2). [2) means quadratic], you can find v(2), and then use the lowest point of circular motion to act as a centripetal force, t-f electricity-g=mv(2) l, you can find t

a A positively charged point charge.

At this time, the positive charge has an attraction effect on the negative charge, and this force can provide the centripetal force of the negative charge to move in a circle; The electric field line of the positive charge is a straight line pointing to infinity from the positive charge, and the negative charge can move in a straight line from rest.

A [Analysis] In the action of the electric field force only by the action of the electric field force on the electric field line, it is possible to achieve as long as the electric field line is straight, but in the uniform circular motion on the equipotential surface, it is necessary for the negatively charged particles to provide centripetal force by the electric field force in the electric field, according to the four electric fields given in the question, the answer A meets both conditions at the same time.

This is a problem of three charge balances, which follows: the large clamp is small, and the same clamp is different (the large amount of charge is on both sides, and the same kind of charge is on both sides), so the C charge is positive, and the charge of C is Q, and the distance R from the B charge is R, then the gravitational force of B on C is equal to the repulsion of A to C, i.e., (KQQ) (R 2)=(4KQQ) [R+L) 2], the gravitational force of C on B is equal to the gravitational force of A on B, i.e., (KQQ) (R 2)=(4KQQ) (L 2), and the solution of the two equations gives R=L, Q=4Q, Therefore, the net charge of the electric limb of c is +4q, which is l away from b

After analysis, it can be seen that to achieve the C charge, it must be located on the right side of the -q shirt. Let the C distance A be R1, let the C distance B be R2, 4KQQ (R1)2=KQQ (R2)2, R1+R2=L. It can be counted as a silver outbreak.

The first point charge c should be in the same line as a and b, otherwise it would be impossible for any of the charges to be in equilibrium by two non-zero non-collinear forces. If you analyze it carefully, you will find that if C is negatively charged, then A is between B and C, but at this time, Ca sets B, C spacing is X, then A,C spacing is X+LLet the charge of c be q again. There are according to the equilibrium conditions.

Upstairs is a fool - petting the dog's head on the 2nd floor and laughing without saying a word.

1.The Coulomb force and the gravitational force are both interaction forces, and they are always reversed, so the momentum is conserved and goes back at the same time, and the neutralization of a p ah emphasizes that the upstairs is a stupid opposite charge before neutralizing it After the collision, the Coulomb force decreases and the kinetic energy will not change back when you go back at the same distance.

2.Conservation of energy, large kinetic energy, small potential energy, and small velocity change after the point q, so the acceleration is very small, so the field strength is small.

3.Examination of questions, examination of topics is very important, and the consequences are serious. As for catching up with this wave or something, it won't be cheap, since I know that it is a kind of oblique throw, then the problem will be solved

The first question is neutralized because of the collision charge, and then analyzed.

I've done it all, but I haven't studied it for half a year, and I've forgotten all the knowledge points...

The answer is to solve 1 4t time from a quarter of a period. We know that at -x0 the velocity of the ball is 0, and then under the action of the electric field force, the acceleration is a=f m=qe m=q 0 md (equation) uniform acceleration linear motion reaches x=0, so there is 1 2a* =x0 so the time to solve t is 1 4t, and t can be solved by bringing in the x0 solved earlier.

If you don't understand it, don't think about it, the finale question is not for everyone, and if you understand one, it will basically not help the next finale question.

Newton's second law, because the field strength is constant, he does a linear motion with uniform variable speed.

bThe magnitude of the increase in gravitational potential energy is equal to the work done by gravity.

The magnitude of the increase in electric potential energy is equal to the work done by the electric field force.

Therefore, the increment of gravitational potential energy and electric potential energy is equal to the total work done by gravity and electric field force according to the kinetic energy theorem, the magnitude of the work done by the external force is equal to the amount of kinetic energy change, and the combined external force contains gravity, tension, and electric field force, obviously, the pulling force is always perpendicular to the direction of motion, so the work done by the pulling force is 0, so the combined external force is equal to the gravity and electric field force to do the attack size, since the initial and termination state velocity of the ball is 0, that is, the kinetic energy change is 0, so the total work done by gravity and electric field force is 0, and the increment of gravitational potential energy and electric potential energy is 0.

c Please follow the analogy of a pendulum.

Position A is the equilibrium position, which is the lowest point of the pendulum, at this time, the direction of the resultant force of gravity and electric field force is exactly along the cycloid.

When moving from B to position A, the single pendulum is at the lowest point and the kinetic energy is maximum.

According to the kinetic energy theorem, the combined external force does positive work, i.e., the potential energy decreases.

c is conserved according to energy.

After release, the ball accelerates.

When the kinetic energy increases, the total energy remains the same, so the other energies decrease.

This ball should do pendulum motion, and both gravitational potential energy and electric field potential energy are conservative energies that are only related to position, so the increase in gravitational potential energy is equal to the decrease in electric field potential energy, b

Choose C, the ball will swing in the equilibrium position at point A, and the ball only has the gravitational electric field force to do work, the sum of gravitational potential energy and electric potential energy and kinetic energy is certain, when the motion reaches point A, the kinetic energy of the ball is the largest, so the gravitational force potential energy and electric potential energy are the smallest, and the kinetic energy increment is greater than zero, so the increment of gravitational potential energy and electric potential energy is negative.

The ball should always be on the equipotential plane, the electric potential energy should not change, and the gravitational potential energy increment is also zero, because the initial and final states are all stationary, theoretically it is the potential kinetic energy potential energy, the external force does not do work, and the energy is not lost halfway. Pick B. It should be...

What I learned five or six years ago...

The ball is acted on by three forces, gravity, tension and electric field force, only gravity and electric field force do work, these two forces do work only change the potential energy and will not change the mechanical energy, because the kinetic energy increases the mechanical energy and does not change, so the potential energy should be reduced, choose c

What is the formula for that computing power, I forget, but the principle is that the same charge is attracted, the heteroelectric charge is repulsed, and the force of q is calculated.