Which in physics is denoted by the letter f. Notations in physics are units of measurement of physical quantities. Units temporarily approved for use

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"

Physical quantity	Symbol		Unit change physical led	Description	Notes
	l, s, d			The extent of an object in one dimension.
	S	square meter		The extent of an object in two dimensions.
Volume, capacity	V	cubic meter		The extent of an object in three dimensions.	extensive quantity
	t			Duration of the event.
Flat angle	α , φ			The amount of change in direction.
Solid angle	α , β , γ	steradian		Part of space
Linear speed	v	meter per second		The speed of changing body coordinates.
Linear acceleration	a,w	meters per second squared		The rate of change in the speed of an object.
Angular velocity	ω	radians per second	rad/s =	Angle change rate.
Angular acceleration	ε	radian per second squared	rad/s 2 =	Rate of change of angular velocity

Table of units of measurement "Mechanics"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
	m	kilogram		A quantity that determines the inertial and gravitational properties of bodies.	extensive quantity
Density	ρ	kilogram per cubic meter	kg/m 3	Mass per unit volume.	intensive quantity
Surface density	ρA	Mass per unit area.	kg/m 2	Ratio of body mass to surface area
Linear density	ρl	Mass per unit length.		Ratio of body mass to its linear parameter
Specific volume	v	cubic meter per kilogram	m 3 /kg	Volume occupied by a unit mass of a substance
Mass flow	Q m	kilogram per second		The mass of a substance that passes through a given area cross section flow per unit time
Volume flow	Q v	cubic meter per second	m 3 /s	Volume flow of liquid or gas
	P	kilogram-meter per second	kg m/s	Product of mass and speed of a body.
Momentum	L	kilogram-meter squared per second	kg m 2 /s	A measure of the rotation of an object.	conserved quantity
	J	kilogram meter squared	kg m 2	A measure of the inertia of an object during rotation.	tensor quantity
Strength, weight	F,Q			An external cause of acceleration acting on an object.
Moment of power	M	newton meter	(kg m 2 /s 2)	The product of a force and the length of a perpendicular drawn from a point to the line of action of the force.
Impulse force	I	newton second		Product of force and the duration of its action
Pressure, mechanical stress	p , σ		Pa = ( kg/(m s 2))	Force per unit area.	intensive quantity
	A		J= (kg m 2 /s 2)	Scalar product forces and movements.
	E,U		J =(kg m 2 /s 2)	The ability of a body or system to do work.	extensive, conserved quantity, scalar
Power	N		W =(kg m 2 /s 3)	Rate of change of energy.

Table of units of measurement "Periodic phenomena, oscillations and waves"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
	T			The period of time during which the system makes one complete oscillation
Batch Process Frequency	v, f			The number of repetitions of an event per unit of time.
Cyclic (circular) frequency	ω	radians per second	rad/s	Cyclic frequency of electromagnetic oscillations in an oscillatory circuit.
Rotation frequency	n	second to the minus first power		Batch process equal to the number full cycles committed per unit of time.
Wavelength	λ			The distance between two points in space closest to each other at which the oscillations occur in the same phase.
Wave number	k	meter to the minus first power		Spatial wave frequency

Units table " Thermal phenomena"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
Temperature	T			Average kinetic energy object particles.	Intensive value
Temperature coefficient	α	kelvin to the minus first power		Dependence of electrical resistance on temperature
Temperature gradient	gradT	kelvin per meter		Change in temperature per unit length in the direction of heat propagation.
Heat (amount of heat)	Q		J =(kg m 2 /s 2)	Energy transferred from one body to another by non-mechanical means
Specific heat	q	joule per kilogram	J/kg	The amount of heat that must be supplied to a substance taken at its melting point in order to melt it.
Heat capacity	C	joule per kelvin		The amount of heat absorbed (released) by a body during the heating process.
Specific heat	c	joule per kilogram kelvin	J/(kg K)	Heat capacity of a unit mass of a substance.
Entropy	S	joule per kilogram	J/kg	A measure of the irreversible dissipation of energy or the uselessness of energy.

Units table " Molecular physics"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
Quantity of substance	v, n		mole	The number of similar structural units that make up a substance.	Extensive value
Molar mass	M , μ	kilogram per mole	kg/mol	The ratio of the mass of a substance to the number of moles of that substance.
Molar energy	H pier	joule per mole	J/mol	Energy of a thermodynamic system.
Molar heat capacity	with a pier	joule per mole kelvin	J/(mol K)	The heat capacity of one mole of a substance.
Molecular concentration	c, n	meter to the minus third power		The number of molecules contained in a unit volume.
Mass concentration	ρ	kilogram per cubic meter	kg/m 3	The ratio of the mass of a component contained in a mixture to the volume of the mixture.
Molar concentration	with a pier	mole per cubic meter	mol/m 3
Ion mobility	IN , μ	square meter per volt second	m 2 /(V s)	The proportionality coefficient between the drift velocity of carriers and the applied external electric field.

Units table " Electricity and magnetism"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
Current strength	I			Charge flowing per unit time.
Current Density	j	ampere per square meter		The strength of electric current flowing through a surface element of unit area.	Vector quantity
Electric charge	Q, q		Cl =(A s)	The ability of bodies to be a source of electromagnetic fields and to take part in electromagnetic interaction.	extensive, conserved quantity
Electric dipole moment	p	coulomb meter		Electrical properties of a system of charged particles in the sense of the field it creates and the effect of external fields on it.
Polarization	P	pendant per square meter	C/m 2	Processes and states associated with the separation of any objects, mainly in space.
Voltage	U			Change in potential energy per unit charge.
Potential, EMF	φ, σ			The work of external forces (non-Coulomb) to move a charge.
	E	volt per meter		The ratio of the force F acting on a stationary point charge placed at a given point in the field to the magnitude of this charge q
Electrical capacity	C			A measure of a conductor's ability to store electrical charge
Electrical resistance	R, r		Ohm =(m 2 kg/(s 3 A 2))	resistance of an object to the passage of electric current
Electrical resistivity	ρ			The ability of a material to prevent the passage of electric current
Electrical conductivity	G			The ability of a body (medium) to conduct electric current
Magnetic induction	B			A vector quantity that is power characteristic magnetic field	Vector quantity
Magnetic flux	F		(kg/(s 2 A))	A value that takes into account the intensity of the magnetic field and the area it occupies.
Magnetic field strength	H	ampere per meter		The difference between the magnetic induction vector B and the magnetization vector M	Vector quantity
Magnetic moment	p m	ampere square meter		A quantity characterizing the magnetic properties of a substance
Magnetization	J	ampere per meter		A quantity characterizing the magnetic state of a macroscopic physical body.	vector quantity
Inductance	L			Proportionality factor between electric shock, flowing in any closed loop, and the total magnetic flux
Electromagnetic energy	N		J =(kg m 2 /s 2)	Energy contained in an electromagnetic field
Volumetric energy density	w	joule per cubic meter	J/m 3	Electric field energy of a capacitor
Active power	P			AC power
Reactive power	Q			A quantity characterizing the loads created in electrical devices by energy fluctuations electromagnetic field in AC circuit
Full power	S	watt-ampere		Total power, taking into account its active and reactive components, as well as deviations of the current and voltage waveforms from harmonic

Units table " Optics, electromagnetic radiation"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
The power of light	J,I			The amount of light energy emitted in a given direction per unit time.	Luminous, extensive value
Light flow	F			Physical quantity characterizing the amount of “light” power in the corresponding radiation flux
Light energy	Q	lumen-second		Physical quantity characterizes the ability of energy transferred by light to cause visual sensations in a person
Illumination	E			The ratio of the luminous flux incident on a small area of ​​a surface to its area.
Luminosity	M	lumen per square meter	lm/m 2	Luminous quantity representing luminous flux
	L, B	candela per square meter	cd/m2	Luminous intensity emitted per unit surface area in a specific direction
Radiation energy	E,W		J =(kg m 2 /s 2)	Energy transferred by optical radiation

Table of units of measurement "Acoustics"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
Sound pressure	p			Variable excess pressure that occurs in elastic medium when a sound wave passes through it
Volume velocity	c, V	cubic meter per second	m 3 /s	The ratio of the volume of raw materials supplied to the reactor per hour to the volume of catalyst
Sound speed	v, u	meter per second		Velocity of propagation of elastic waves in a medium
Sound intensity	l	watt per square meter	W/m2	A quantity characterizing the power transferred by a sound wave in the direction of propagation	scalar physical quantity
Acoustic impedance	Z a , R a	pascal second per cubic meter	Pa s/m 3	The ratio of the amplitude of sound pressure in a medium to the vibrational speed of its particles when a sound wave passes through the medium
Mechanical resistance	R m	newton second per meter	N s/m	Indicates the force required to move a body at each frequency

Units table " Atomic and nuclear physics. Radioactivity"

Physical quantity	Symbol	Unit of measurement of physical quantity	Unit change physical led	Description	Notes
Mass (rest mass)	m	kilogram		The mass of an object at rest.
Mass defect	Δ	kilogram		A quantity expressing the influence of internal interactions on the mass of a composite particle
Elementary electric charge	e			The minimum portion (quantum) of electric charge observed in nature in free long-lived particles
Communication energy	E St		J =(kg m 2 /s 2)	The difference between the energy of a state in which the constituent parts of the system are infinitely distant
Half-life, average lifetime	T, τ			The time during which the system decays in the approximate ratio of 1/2
Effective cross section	σ	square meter		A quantity characterizing the probability of interaction of an elementary particle with atomic nucleus or another particle
Nuclide activity		becquerel		A value equal to the ratio of the total number of decays of radioactive nuclide nuclei in the source to the decay time
Energy of ionizing radiation	E,W		J =(kg m 2 /s 2)	Type of energy released by atoms in the form of electromagnetic waves (gamma or x-rays) or particles
Absorbed dose of ionizing radiation	D			The dose at which 1 joule of ionizing radiation energy is transferred to a mass of 1 kg
Equivalent dose of ionizing radiation	H , D eq			Absorbed dose of any ionizing radiation equal to 100 erg per 1 gram of irradiated substance
Exposure dose of X-ray and gamma radiation	X	pendant per kilogram	C/kg	ratio of the total electric charge of ions of the same sign from external gamma radiation

Physics notation with multiple letters

To designate some quantities, several letters or individual words or abbreviations are sometimes used. Thus, a constant value in the formula is often denoted as

The differential is indicated by a small letter

Before the name of the quantity, for example .

Special symbols

For ease of writing and reading, it is customary among physicists to use special symbols that characterize certain phenomena and properties.

In physics, it is customary to use not only formulas that are used in mathematics, but also specialized brackets.

Diacritics

Diacritics are added to the symbol of a physical quantity to indicate certain differences. Below, diacritics have been added to the letter x as an example.

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Books

• Hydraulics. Textbook and workshop for academic bachelor's degree, V.A. Kudinov. The textbook outlines the basic physical and mechanical properties of liquids, issues of hydrostatics and hydrodynamics, provides the basics of the theory of hydrodynamic similarity and mathematical modeling...
• Hydraulics 4th ed., trans. and additional Textbook and workshop for academic bachelor's degree, Eduard Mikhailovich Kartashov. The textbook outlines the basic physical and mechanical properties of liquids, issues of hydrostatics and hydrodynamics, provides the basics of the theory of hydrodynamic similarity and mathematical modeling...

It's no secret that there are special notations for quantities in any science. Letter designations in physics prove that this science is no exception in terms of identifying quantities using special symbols. There are quite a lot of basic quantities, as well as their derivatives, each of which has its own symbol. So, letter designations in physics are discussed in detail in this article.

Physics and basic physical quantities

Thanks to Aristotle, the word physics began to be used, since it was he who first used this term, which at that time was considered synonymous with the term philosophy. This is due to the commonality of the object of study - the laws of the Universe, more specifically - how it functions. As you know, the first scientific revolution took place in the 16th-17th centuries, and it was thanks to it that physics was singled out as an independent science.

Mikhail Vasilyevich Lomonosov introduced the word physics into the Russian language by publishing a textbook translated from German - the first physics textbook in Russia.

So, physics is a branch of natural science devoted to the study of the general laws of nature, as well as matter, its movement and structure. There are not as many basic physical quantities as it might seem at first glance - there are only 7 of them:

• length,
• weight,
• time,
• current strength,
• temperature,
• amount of substance
• the power of light.

Of course, they have their own letter designations in physics. For example, the symbol chosen for mass is m, and for temperature - T. Also, all quantities have their own unit of measurement: the luminous intensity is candela (cd), and the unit of measurement for the amount of substance is mole.

Derived physical quantities

There are much more derivative physical quantities than basic ones. There are 26 of them, and often some of them are attributed to the main ones.

So, area is a derivative of length, volume is also a derivative of length, speed is a derivative of time, length, and acceleration, in turn, characterizes the rate of change in speed. Momentum is expressed through mass and speed, force is the product of mass and acceleration, mechanical work depends on force and length, energy is proportional to mass. Power, pressure, density, surface density, linear density, amount of heat, voltage, electrical resistance, magnetic flux, moment of inertia, moment of impulse, moment of force - they all depend on mass. Frequency, angular velocity, angular acceleration are inversely proportional to time, and electric charge is directly dependent on time. Angle and solid angle are derived quantities from length.

What letter represents voltage in physics? Voltage, which is a scalar quantity, is denoted by the letter U. For speed, the designation is the letter v, for mechanical work - A, and for energy - E. Electric charge is usually denoted by the letter q, and magnetic flux - F.

SI: general information

The International System of Units (SI) is a system of physical units that is based on the International System of Units, including the names and designations of physical quantities. It was adopted by the General Conference on Weights and Measures. It is this system that regulates letter designations in physics, as well as their dimensions and units of measurement. Letters of the Latin alphabet are used for designation, and in some cases - of the Greek alphabet. It is also possible to use special characters as a designation.

Conclusion

So, in any scientific discipline there are special designations for various kinds of quantities. Naturally, physics is no exception. There are quite a lot of letter symbols: force, area, mass, acceleration, voltage, etc. They have their own symbols. There is a special system called the International System of Units. It is believed that basic units cannot be mathematically derived from others. Derivative quantities are obtained by multiplying and dividing from basic quantities.

Constructing drawings is not an easy task, but without it modern world no way. After all, in order to make even the most ordinary item (a tiny bolt or nut, a shelf for books, the design of a new dress, etc.), you first need to carry out the appropriate calculations and draw a drawing of the future product. However, often one person draws it up, and another person produces something according to this scheme.

To avoid confusion in understanding the depicted object and its parameters, conventions for length, width, height and other quantities used in design are accepted all over the world. What are they? Let's find out.

Quantities

Area, height and other designations of a similar nature are not only physical, but also mathematical quantities.

Their single letter designation (used by all countries) was established in the mid-twentieth century by the International System of Units (SI) and is still used to this day. It is for this reason that all such parameters are designated by Latin, and not in Cyrillic letters or Arabic script. In order not to create individual difficulties, when developing design documentation standards in most modern countries it was decided to use practically the same symbols that are used in physics or geometry.

Any school graduate remembers that depending on whether a two-dimensional or three-dimensional figure (product) is depicted in the drawing, it has a set of basic parameters. If there are two dimensions, these are width and length, if there are three, height is also added.

So, first, let's find out how to correctly indicate length, width, height in the drawings.

Width

As mentioned above, in mathematics the quantity in question is one of the three spatial dimensions of any object, provided that its measurements are made in the transverse direction. So what is width famous for? It is designated by the letter “B”. This is known all over the world. Moreover, according to GOST, it is permissible to use both capital and lowercase Latin letters. The question often arises as to why this particular letter was chosen. After all, the reduction is usually made according to the first Greek or English name of the quantity. In this case, the width in English will look like “width”.

Probably the point here is that this parameter was initially most widely used in geometry. In this science, when describing figures, length, width, height are often denoted by the letters “a”, “b”, “c”. According to this tradition, when choosing, the letter "B" (or "b") was borrowed from the SI system (although symbols other than geometric ones began to be used for the other two dimensions).

Most believe that this was done so as not to confuse width (designated with the letter "B"/"b") with weight. The fact is that the latter is sometimes referred to as “W” (short for the English name weight), although the use of other letters (“G” and “P”) is also acceptable. According to international standards of the SI system, width is measured in meters or multiples (multiples) of their units. It is worth noting that in geometry it is sometimes also acceptable to use “w” to denote width, but in physics and other exact sciences such a designation is usually not used.

Length

As already indicated, in mathematics, length, height, width are three spatial dimensions. Moreover, if width is a linear dimension in the transverse direction, then length is in the longitudinal direction. Considering it as a quantity of physics, one can understand that this word means a numerical characteristic of the length of lines.

IN English language this term is called length. It is because of this that this value is denoted by the capital or lowercase initial letter of the word - “L”. Like width, length is measured in meters or their multiples (multiples).

Height

The presence of this value indicates that we have to deal with a more complex - three-dimensional space. Unlike length and width, height numerically characterizes the size of an object in the vertical direction.

In English it is written as "height". Therefore, according to international standards, it is denoted by the Latin letter “H” / “h”. In addition to height, in drawings sometimes this letter also acts as a designation for depth. Height, width and length - all these parameters are measured in meters and their multiples and submultiples (kilometers, centimeters, millimeters, etc.).

Radius and diameter

In addition to the parameters discussed, when drawing up drawings you have to deal with others.

For example, when working with circles, it becomes necessary to determine their radius. This is the name of the segment that connects two points. The first of them is the center. The second is located directly on the circle itself. In Latin this word looks like "radius". Hence the lowercase or capital “R”/“r”.

When drawing circles, in addition to the radius, you often have to deal with a phenomenon close to it - diameter. It is also a line segment connecting two points on a circle. In this case, it necessarily passes through the center.

Numerically, the diameter is equal to two radii. In English this word is written like this: "diameter". Hence the abbreviation - large or small Latin letter “D” / “d”. Often the diameter in the drawings is indicated using a crossed out circle - “Ø”.

Although this is a common abbreviation, it is worth keeping in mind that GOST provides for the use of only the Latin “D” / “d”.

Thickness

Most of us remember school lessons mathematics. Even then, teachers told us that it is customary to use the Latin letter “s” to denote a quantity such as area. However, according to generally accepted standards, a completely different parameter is written in drawings in this way - thickness.

Why is that? It is known that in the case of height, width, length, the designation by letters could be explained by their writing or tradition. It’s just that thickness in English looks like “thickness”, and in Latin it looks like “crassities”. It is also not clear why, unlike other quantities, thickness can only be indicated in lowercase letters. The notation "s" is also used to describe the thickness of pages, walls, ribs, etc.

Perimeter and area

Unlike all the quantities listed above, the word “perimeter” does not come from Latin or English, but from Greek. It is derived from "περιμετρέο" ("measure the circumference"). And today this term has retained its meaning (the total length of the boundaries of the figure). Subsequently, the word entered the English language (“perimeter”) and was fixed in the SI system in the form of an abbreviation with the letter “P”.

Area is a quantity showing a quantitative characteristic geometric figure having two dimensions (length and width). Unlike everything listed earlier, it is measured in square meters (as well as in submultiples and multiples thereof). As for the letter designation of the area, it differs in different areas. For example, in mathematics this is the Latin letter “S”, familiar to everyone since childhood. Why this is so - no information.

Some people unknowingly think that this is due to the English spelling of the word "square". However, in it the mathematical area is "area", and "square" is the area in the architectural sense. By the way, it is worth remembering that “square” is the name of the geometric figure “square”. So you should be careful when studying drawings in English. Due to the translation of “area” in some disciplines, the letter “A” is used as a designation. In rare cases, "F" is also used, but in physics this letter stands for a quantity called "force" ("fortis").

Other common abbreviations

The designations for height, width, length, thickness, radius, and diameter are the most commonly used when drawing up drawings. However, there are other quantities that are also often present in them. For example, lowercase "t". In physics this means “temperature”, but according to GOST Unified system design documentation, this letter is a step (coil springs, etc.). However, it is not used when it comes to gears and threads.

The capital and lowercase letter “A”/“a” (according to the same standards) in the drawings is used to denote not the area, but the center-to-center and center-to-center distance. In addition to different sizes, in drawings it is often necessary to indicate angles of different sizes. For this purpose, it is customary to use lowercase letters of the Greek alphabet. The most commonly used are “α”, “β”, “γ” and “δ”. However, it is acceptable to use others.

What standard defines the letter designation of length, width, height, area and other quantities?

As mentioned above, so that there is no misunderstanding when reading the drawing, representatives of different nations have adopted common standards for letter designation. In other words, if you are in doubt about the interpretation of a particular abbreviation, look at GOSTs. This way you will learn how to correctly indicate height, width, length, diameter, radius, and so on.

Studying physics at school lasts several years. At the same time, students are faced with the problem that the same letters represent completely different quantities. Most often this fact concerns Latin letters. How then to solve problems?

There is no need to be afraid of such a repetition. Scientists tried to introduce them into the notation so that identical letters would not appear in the same formula. Most often, students encounter the Latin n. It can be lowercase or uppercase. Therefore, the question logically arises about what n is in physics, that is, in a certain formula encountered by the student.

What does the capital letter N stand for in physics?

Most often in school course it occurs in the study of mechanics. After all, there it can be immediately in spirit meanings - the power and strength of a normal support reaction. Naturally, these concepts do not overlap, because they are used in different sections of mechanics and are measured in different units. Therefore, you always need to define exactly what n is in physics.

Power is the rate of change of energy in a system. This is a scalar quantity, that is, just a number. Its unit of measurement is the watt (W).

The normal ground reaction force is the force exerted on the body by the support or suspension. In addition to the numerical value, it has a direction, that is, it is a vector quantity. Moreover, it is always perpendicular to the surface on which the external influence is made. The unit of this N is newton (N).

What is N in physics, in addition to the quantities already indicated? It could be:

Avogadro's constant;

magnification of the optical device;

substance concentration;

Debye number;

total radiation power.

What does the lowercase letter n stand for in physics?

The list of names that may be hidden behind it is quite extensive. The notation n in physics is used for the following concepts:

refractive index, and it can be absolute or relative;

neutron - a neutral elementary particle with a mass slightly greater than that of a proton;

rotation frequency (used to replace the Greek letter "nu", since it is very similar to the Latin "ve") - the number of repetitions of revolutions per unit of time, measured in hertz (Hz).

What does n mean in physics, besides the quantities already indicated? It turns out that it hides the fundamental quantum number (quantum physics), concentration and Loschmidt constant (molecular physics). By the way, when calculating the concentration of a substance, you need to know the value, which is also written with the Latin “en”. It will be discussed below.

What physical quantity can be denoted by n and N?

Its name comes from Latin word numerus, translated it sounds like “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.

Formulas containing capital N

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

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 should divide the number of particles by Avogadro's number:

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:

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

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

Formulas containing lowercase n

In a school physics course, this letter is most often associated with the refractive index of a substance. Therefore, it is important to know the formulas with its application.

So, for the absolute refractive index the formula is written as follows:

Here c is the speed of light in a vacuum, v is its speed in a refractive medium.

Formula for relative indicator refraction is somewhat more complicated:

n 21 = v 1: v 2 = n 2: n 1,

where n 1 and n 2 are the absolute refractive indices of the first and second medium, v 1 and v 2 are the speeds of the light wave in these substances.

How to find n in physics? A formula will help us with this, which requires knowing the angles of incidence and refraction of the beam, that is, n 21 = sin α: sin γ.

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.

Power task

№1. During plowing, the tractor pulls the plow evenly. At the same time, he applies a force of 10 kN. With this movement, it covers 1.2 km within 10 minutes. It is necessary to determine the power it develops.

Converting units to SI. You can start with force, 10 N is equal to 10000 N. Then the distance: 1.2 × 1000 = 1200 m. Time left - 10 × 60 = 600 s.

Selection of formulas. As mentioned above, N = A: t. But the task has no meaning for the work. To calculate it, another formula is useful: A = F × S. The final form of the formula for power looks like this: N = (F × S) : t.

Solution. Let's first calculate the work and then the power. Then the first action gives 10,000 × 1,200 = 12,000,000 J. The second action gives 12,000,000: 600 = 20,000 W.

Answer. The tractor power is 20,000 W.

Refractive index problems

№2. The absolute refractive index of glass is 1.5. The speed of light propagation in glass is less than in vacuum. You need to determine how many times.

There is no need to convert data to SI.

When choosing formulas, you need to focus on this one: n = c: v.

Solution. From this formula it is clear that v = c: n. This means that the speed of light in glass is equal to the speed of light in a vacuum divided by the refractive index. That is, it decreases by one and a half times.

Answer. The speed of light propagation in glass is 1.5 times less than in vacuum.

№3. There are two transparent media available. The speed of light in the first of them is 225,000 km/s, in the second it is 25,000 km/s less. A ray of light goes from the first medium to the second. The angle of incidence α is 30º. Calculate the value of the angle of refraction.

Do I need to convert to SI? Speeds are given in non-systemic units. However, when substituted into formulas, they will be reduced. Therefore, there is no need to convert speeds to m/s.

Selecting the formulas necessary to solve the problem. You will need to use the law of light refraction: n 21 = sin α: sin γ. And also: n = c: v.

Solution. In the first formula, n 21 is the ratio of the two refractive indices of the substances in question, that is, n 2 and n 1. If we write down the second indicated formula for the proposed media, we get the following: n 1 = c: v 1 and n 2 = c: v 2. If we make the ratio of the last two expressions, it turns out that n 21 = v 1: v 2. Substituting it into the formula for the law of refraction, we can derive the following expression for the sine of the refraction angle: sin γ = sin α × (v 2: v 1).

We substitute the values ​​of the indicated speeds and the sine of 30º (equal to 0.5) into the formula, it turns out that the sine of the refraction angle is equal to 0.44. According to the Bradis table, it turns out that the angle γ is equal to 26º.

Answer. The refraction angle is 26º.

Tasks for the circulation period

№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.

№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.

Let's sum it up

When a student encounters a formula containing n or N in a physics problem, he needs deal with two points. The first is from what branch of physics the equality is given. This may be clear from the title in the textbook, reference book, or the words of the teacher. Then you should decide what is hidden behind the many-sided “en”. Moreover, the name of the units of measurement helps with this, if, of course, its value is given. Another option is also allowed: look carefully at the remaining letters in the formula. Perhaps they will turn out to be familiar and will give a hint on the issue at hand.