When measuring the electric field, why is it required to test the electricity of the test and replac

Electric field lines can never cross like magnetic field lines, an electron with a radiant electric field, if put into a uniform electric field, then the electric field of this space will change, there is only one electric field in a space, it is produced after the interaction of all charges in space, it is not that there is a uniform electric field A and a small radiated electric field B in this space at the same time, and they do not interfere with each other.

For example, if you use a chopstick to touch the water surface and then stand still, you will find that the water surface is not flat, and the circle near the toothpick is protruding, if you want to measure the length of the chopsticks dipped in the water to detect the depth of the water, the height of the wet chopsticks is obviously a few microns higher than the normal water surface height. This is the same concept as electrons being placed in a uniform electric field. There is some impact, and of course try to have as little impact as possible.

It's not something you don't think! The fact is that too much charge will affect the original electric field! And at the same time, the volume should be small, so that it is accurate to describe the electric field strength at a certain point!

The electric field you measure is actually the strength of the electric field. is a vector. It's not just size.

What's more important is to have direction! If the charge carried by the measured charge is too large. What happens when the electric field it produces is superimposed on the original electric field?

The direction has changed, and the size has changed. So this requirement is necessary!

The small amount of charge can be used as a perfect model for the physical unit electron, which would otherwise be neutralized by electricity or a single electromagnetic field would form to interfere with the test.

The electric field is subject to a reaction force, and the mass of the tentative charge is small enough to be negligible.

1. Your formula is wrong, e is the formula, but from the formula, the charge is removed, but in fact, when there is no charge, the electric field is like this, that is, the difference of the electric field in space is only related to the original charge, if you put another charge in this field, no matter how small it is, he will definitely destroy the electric field formed by the original charge, which is not reflected in the formula, so the test charge is required to be as small as possible! to minimize the impact!

2. The point charge can achieve as little damage to the original field as possible, if it is a parallel plate capacitor, the effect on the detection electric field will even make him rearrange it from a new arrangement to a parallel field strength! For non-point charges, just integrate the detected charges in the formula, and there is no inapplicability!

3. The difference is that the influence of a small charge on the original electric field is negligible, and a large charge will seriously destroy the original field!

4. In a word, although it is required that the tentative charge is small enough, according to the calculation formula e=(kq r 2), the accurate electric field strength can be calculated, but if the tentative charge is not small enough and the actual deviation is there?

In a word, yes, the calculation formula is right, the calculation results of the test charge are all right, the actual situation is that no matter how small the test charge is, he forms his own electric field, superimposes with the original electric field, destroys the original electric field, and makes the actual value deviate from the counting value, but the power is small, the deviation is small, and it can be ignored!

The electric field of the original charge will not affect the electric field of the original charge.

When studying the properties of the electric field, such as the small and direction of the field strength at a certain point in the electric field, the electric potential of a certain point in the electric field, etc., it is often necessary to put a tentative charge at a certain point in the electric field, and then determine the properties of the point in the electric field (the nature of the force - field strength, the nature of energy - electric potential) according to the electric field force and the electric potential energy of the tentative charge at that point. Because the tentative charge is used to determine the properties of a point in the electric field, it is characterized by its small size and small amount of charge (which does not affect the field strength distribution of the original electric field). In addition, the test charge is also called the test charge.

The test charge is the ideal charge introduced when describing the electric field. We know that there is an electric field around an electric charge, and in order to describe an electric field that already exists, it is necessary to take advantage of one of the fundamental properties of the electric field: the strong effect on the charge placed in the electric field.

However, an electric field is also generated on the charge placed in the electric field, so that the original electric field is destroyed. Therefore, in order to study the original electric field, it is necessary to have requirements for putting in the electric field, that is, the electric field generated by this charge must have no effect on the original electric field, so it is required that the amount of charge of this charge should be as small as possible, and the most ideal situation is that this charge must have an amount of charge, so as to study the original electric field, but this charge cannot produce an electric field by itself. Then such a charge is practically non-existent.

This charge is called an ideal charge, or a test (i.e., a test of the electric field) charge. According to such a requirement, of course, there are also positive and negative charges to be tested.

Knowledge is ultimately applied to practice, and the formula requires a point charge, which is similar in size to a unit, and is mainly convenient to use. It's okay to use a small amount of electricity, but you're not good at it. With a lot, you understand, there will be an impact. Also, you are wrong in the formula.

If it weren't for the point charge Coulomb's law, it wouldn't work.

One may not have much impact, but several?

In order not to affect the electric field it is intended to detect, it is required to have a small amount of charge.

For example, in order to measure the field strength of a uniform electric field, if the amount of tentative charge is very large, the electric field itself cannot be ignored, and the electric field to be measured is changed, for example, the shape of the electric field line becomes curved and is no longer a parallel straight line.

Similarly, the mass of the ball is very small (compared with the earth) when the gravitational acceleration of the earth's surface is measured by the motion of the free fall, otherwise, if a small ball (such as a black hole) with a similar mass of the earth is used for experiments, the area of the experiment is no longer a gravitational field source of the earth, but the gravitational field caused by the small black hole and the earth, so the measured gravitational acceleration is not the gravitational field of the earth.

The charge used to detect the electric field is called the test charge, also called the test charge.

It must be required that the amount of tentative charge to detect the strength of the electric field be sufficiently small. Specifically, there are two requirements:

First, the introduction of a test charge into the electric field does not change the distribution of the original electric field. This cannot be done if the charge of the tentative charge is not small enough.

Second, the test charge must be able to look at the point of action. to test the field strength at each point in the electric field.

The magnitude and direction of the electric field at a point is measured.

If the volume is very large, how do you call it a point?

The electric power is small, that is, the electric field generated by the test charge itself should be small, so as not to affect the electric field to be measured.

What is tested is an electric field, and as for what this electric field is made of, feel free.

The test charge is a positive charge, and the direction of the force is the direction of the electric field.

Although you have to use a negative charge, then it is not bad to use the opposite direction of the force as the direction of the electric field. But why bother?

We know that the electric field is formed by a point charge with a large amount of charge, and if the amount of tentative charge is very large, then it can generate a new electric field that can be compared with the original electric field, resulting in inaccurate measurements.

Since the electric fields of the two charged bodies will affect each other, in order to minimize the influence of the tentative charge on the original electric field, the tentative charge must carry a sufficiently small amount of electricity (meta-charge) and at the same time have a sufficiently small linearity.