What are the uses of electric power
The sequence is divided into the following sections:
- Coulomb's law
- Analogies to gravity
- Electric field
- Electric field strength
To display the measurement curve, please click on the magnifying glass
An experiment is used to investigate the dependence of the electric force on the distance between the two charges.
The evaluation of the measurement curve provides a 1 / r² dependency. It is plausible that the electric force is also proportional to each of the two charges q and Q and thus only the proportionality factor is missing for the force formula.
Theoretical derivation of the law of force (please click on the magnifying glass)
In another context, physicists introduced the electric field constant. A theoretical derivation of the law of force therefore provides the strange expression 1 / (4 π · ε0) for the proportionality factor. This law was found by the same physicist after whom the unit of charge is named. That is why one speaks of Coulomb forces.
2. Analogies to gravitation
It is no coincidence that the structure of Coulomb's law is completely analogous to the law of gravitation. Both times it is about the force effect of two bodies, which, in simplified terms, can be imagined as point-shaped. The product of charges or masses in the meters is plausible. The 1 / r² dependency can later be explained clearly with the concept of the electric field.
Using the example of a pair of elephants, the magnitudes of the electrical and gravitational forces are compared. Even with very large masses and comparatively low charges, the electrical force predominates. The reason lies in the different sizes for the factors: 1 / (4π · ε0) results in about 10 in the SI system10; on the other hand, the gravitational constant is much smaller at about 10ˉ¹º.
The fact that we rarely observe electrical forces in everyday life, but above all gravitational forces, suggests that the objects are mostly uncharged.
Example of an electric field
An experiment shows why the choice of words "field" is very appropriate. Plastic drinking straws are arranged around a strongly positively charged ball. In these, due to the forces acting on the spherical charge, the positive charges move outwards and the negative charges inwards. A so-called is created electric dipole, which shows the direction of the force. It looks like the stalks in a cornfield in which the wind has blown eddies.
If we now assume with Coulomb's law that one charge is much larger than the other, then we arrive at the concept of electric field. The small load q we refer to as Test chargethat are in the space around the big cargo Q felt a force. A field line shows the direction of the force, the density of the field lines is a measure of the strength of the electrical force in this area.
Basics about field lines
The electric field lines run at every point in the room in the direction of the force on a positive test charge.
If you double the radius, the area of a sphere around the center of the radially symmetrical field quadruples. This is the clear explanation promised above for the 1 / r² dependence of the electrical force.
With radial fields of positive and negative point charge as building blocks, the fields of any charge arrangement can be constructed, for example the field of a dipole.
Examples of different arrangements of field lines:
4. Electric field strength
Formula for the electric field strength
The strength of an electric field is naturally defined by the force acting on a test charge. However, so that the size of the test charge has no influence, the quotient of the force and the test charge is used. The unity of electric field strengthE. is by its definition equal to Newton through Coulomb.
There is a direct measuring device for electric field strengths. The way it works is a bit complicated: A metal impeller rotates in front of two nested wing surfaces that are electrically isolated from each other. In between, the actually constant field is periodically faded in and out. The resulting alternating current is a measure of the strength of the constant electric field.
Some measurements are carried out with this measuring device: Large values are obtained near a charged sphere and in front of a tube television set.
There are various important technical applications for strong electric fields.
It used to be difficult to paint a car in such a way that the same paint thickness was created in the grooves and on surfaces facing away from the vehicle. The usual today electrostatic painting a strong electric field is applied between the body and the spray guns. Therefore, the color pigments move approximately on field lines and also reach remote areas on these curved paths.
Another important application is that electrostatic flue gas cleaning.
Electrostatic flue gas cleaning
Soot particles are removed from the exhaust gas in a strong electric field. In the model experiment, smoke is passed through a pipe with a wire charged with high voltage stretched along its central axis.
Electric too Photocopying is an application of the effects of electric force. A model test shows that the black toner powder only adheres to the areas of the paper that have been electrically charged. In the copier, charge is first sprayed over the entire surface of the copy paper. The optical image of the original on the copy paper discharges these charges wherever light strikes. Therefore, the toner only sticks to the dark areas and a copy of the original is created.
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