Notation in physics - units of measurement of physical quantities

Each measurement is a comparison of the measured quantity with another homogeneous quantity, which is considered unitary. Theoretically, the units for all quantities in physics can be chosen to be independent of each other. But this is extremely inconvenient, since for each value one should enter its own standard. In addition, in all physical equations that reflect the relationship between different quantities, numerical coefficients would arise.

The main feature of the currently used systems of units is that there are certain relationships between units of different quantities. These relationships are established by the physical laws (definitions) that relate the measured quantities to each other. Thus, the unit of speed is chosen in such a way that it is expressed in terms of units of distance and time. When selecting speed units, the speed definition is used. The unit of force, for example, is established using Newton's second law.

When constructing a specific system of units, several physical quantities are selected, the units of which are set independently of each other. Units of such quantities are called basic. The units of other quantities are expressed in terms of the basic ones, they are called derivatives.

Table of units of measurement “Space and time”

Series and parallel connection of capacitors

Capacitors can be connected in series or in parallel, resulting in a set with new characteristics.

Parallel connection

If you connect capacitors in parallel, then the total capacity of the resulting battery is equal to the sum of all the capacitances of its components. If the battery consists of capacitors of identical design, this can be considered as adding the area of ​​all the plates. In this case, the voltage on each battery cell will be the same, and the charges will add up. For three parallel connected capacitors:

• U=U1=U2=U3;
• q=q1+q2+q3;
• C=C1+C2+C3.

Table of units of measurement "Mechanics"

Law of gravitation

Every object in the Universe is attracted to every other object with a force proportional to their masses and inversely proportional to the square of the distance between them.

${\large F = G \cdot \dfrac {m \cdot M}{R^2}}$

We can add that any body reacts to a force applied to it with acceleration in the direction of this force, in magnitude inversely proportional to the mass of the body.

${\large G}$ — gravitational constant

${\large M}$ — mass of the earth

${\large R}$ — radius of the earth

${\large G = 6.67 \cdot {10^{-11}} \left ( \dfrac {m^3}{kg \cdot {sec}^2} \right ) }$

${\large M = 5.97 \cdot {10^{24}} \left ( kg \right ) }$

${\large R = 6.37 \cdot {10^{6}} \left ( m \right ) }$

Within the framework of classical mechanics, gravitational interaction is described by Newton's law of universal gravitation, according to which the force of gravitational attraction between two bodies of mass ${\large m_1}$ and ${\large m_2}$ separated by a distance ${\large R}$ is

${\large F = -G \cdot \dfrac {m_1 \cdot m_2}{R^2}}$ Here ${\large G}$ is the gravitational constant equal to ${\large 6.673 \cdot {10^{- 11}} m^3 / \left ( kg \cdot {sec}^2 \right ) }$. The minus sign means that the force acting on the test body is always directed along the radius vector from the test body to the source of the gravitational field, i.e. gravitational interaction always leads to the attraction of bodies. The gravity field is potential. This means that you can introduce the potential energy of gravitational attraction of a pair of bodies, and this energy will not change after moving the bodies along a closed loop. The potentiality of the gravitational field entails the law of conservation of the sum of kinetic and potential energy, which, when studying the motion of bodies in a gravitational field, often significantly simplifies the solution. Within the framework of Newtonian mechanics, gravitational interaction is long-range. This means that no matter how a massive body moves, at any point in space the gravitational potential and force depend only on the position of the body at a given moment in time.

Table of units of measurement “Periodic phenomena, oscillations and waves”

Newton's second and third laws

The interaction of bodies can be described using the concept of force. Force is a vector quantity that is a measure of the influence of one body on another. Being a vector, force is characterized by its modulus (absolute value) and direction in space. In addition, the point of application of the force is important: the same force in magnitude and direction, applied at different points of the body, can have different effects. So, if you grab the rim of a bicycle wheel and pull tangentially to the rim, the wheel will begin to rotate. If you pull along the radius, there will be no rotation.

Newton's second law

The product of the body mass and the acceleration vector is the resultant of all forces applied to the body:

${\large m \cdot \overrightarrow{a} = \overrightarrow{F} }$

Newton's second law relates acceleration and force vectors. This means that the following statements are true.

1. ${\large m \cdot a = F}$, where ${\large a}$ is the acceleration modulus, ${\large F}$ is the resulting force modulus.
2. The acceleration vector has the same direction as the resultant force vector, since the mass of the body is positive.

Newton's third law

Two bodies act on each other with forces equal in magnitude and opposite in direction. These forces have the same physical nature and are directed along a straight line connecting their points of application.

Table of units of measurement “Thermal phenomena”

What is n equal to in physics if it is the refractive index?

Typically, tables give values ​​for the absolute refractive indices of various substances. Do not forget that this value depends not only on the properties of the medium, but also on the wavelength. Table values ​​of the refractive index are given for the optical range.

So, it became clear what n is in physics. To avoid any questions, it is worth considering some examples.

Table of units of measurement "Molecular physics"

What physical quantity can be denoted by n and N?

Its name comes from the Latin word numerus, translated as “number”, “quantity”. Therefore, the answer to the question of what n means in physics is quite simple. This is the number of any objects, bodies, particles - everything that is discussed in a certain task.

Moreover, “quantity” is one of the few physical quantities that do not have a unit of measurement. It's just a number, without a name. For example, if the problem involves 10 particles, then n will simply be equal to 10. But if it turns out that the lowercase “en” is already taken, then you have to use a capital letter.

Table of units of measurement "Electricity and magnetism"

Table 3 IMPORTANT SI DERIVATIVE UNITS

APPLICATIONS

Appendix A The most common stylistic mistakes.

Appendix B Norms of Russian-language technical literature.

Appendix B Examples of translation of some frequently used terms.

Appendix D “False friends” of the translator.

Appendix E Presentation of numbers, monetary amounts and dates

Appendix E Additional requirements for translations that require notarization of the authenticity of the translator's signature.

Appendix G Features of translating descriptions of software products.

Appendix 3 Recommendations for setting up MS Word before starting translation.

Appendix I Some features of typing in foreign languages.

Appendix K Directory of units of measurement. part 2 part 3 part 4

Appendix L Transliteration rules.

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Table of units of measurement “Optics, electromagnetic radiation”

Tasks for the circulation period

No. 4. The blades of a windmill rotate with a period of 5 seconds. Calculate the number of revolutions of these blades in 1 hour.

You only need to convert time to SI units for 1 hour. It will be equal to 3,600 seconds.

Selection of formulas. The period of rotation and the number of revolutions are related by the formula T = t: N.

Solution. From the above formula, the number of revolutions is determined by the ratio of time to period. Thus, N = 3600: 5 = 720.

Answer. The number of revolutions of the mill blades is 720.

No. 5. An airplane propeller rotates at a frequency of 25 Hz. How long will it take the propeller to make 3,000 revolutions?

All data is given in SI, so there is no need to translate anything.

Required formula: frequency ν = N: t. From it you only need to derive the formula for the unknown time. It is a divisor, so it is supposed to be found by dividing N by ν.

Solution. Dividing 3,000 by 25 gives the number 120. It will be measured in seconds.

Answer. An airplane propeller makes 3000 revolutions in 120 s.

Table of units of measurement "Acoustics"

Some practical capacitor designs

In practice, various designs of flat capacitors are used. The design of the device determines its characteristics and scope of application.

Variable capacitor

A common type of variable capacitor (VCA) consists of a block of moving and fixed plates separated by air or a solid insulator. The moving plates rotate around an axis, increasing or decreasing the overlap area. When the moving block is removed, the interelectrode gap remains unchanged, but the average distance between the plates also increases. The dielectric constant of the insulator also remains unchanged. The capacity is adjusted by changing the area of ​​the plates and the average distance between them.

KPI in the position of maximum (left) and minimum (right) capacity

Oxide capacitor

Previously, such a capacitor was called electrolytic. It consists of two strips of foil separated by a paper dielectric impregnated with electrolyte. The first strip serves as one plate, the second plate serves as the electrolyte. The dielectric is a thin layer of oxide on one of the metal strips, and the second strip serves as a current collector.

Table of units of measurement “Atomic and nuclear physics. Radioactivity"

Formulas containing capital N

The first of them determines power, which is equal to the ratio of work to time:

N = A: t.

In molecular physics there is such a thing as the chemical amount of a substance. Denoted by the Greek letter "nu". To count it, you need to divide the number of particles by Avogadro's number:

ν = N:NA.

By the way, the last value is also denoted by the so popular letter N. Only it always has a subscript - A.

To determine the electric charge, you will need the formula:

q = N × e.

Another formula with N in physics is oscillation frequency. To count it, you need to divide their number by time:

ν = N : t.

The letter “en” appears in the formula for the circulation period:

T = t: N.