Electromagnet Magnetic force calculation problem? Ask the experts for help!

Many of them are empirical formulas. I am not sure whether the formulas are correct or not, but from the perspective of influencing factors, they are still consistent with the rules.

Questions 1 and 4 are the same. The problem, simply put, is the lifting distance between the magnet and the object. For question 2, just choose the unit of the International System of Units. For question 3, the magnetic force is related to the magnetic flux, and the magnetic flux is related to the area and has nothing to do with the length. Naturally, it has nothing to do with the length of the iron core

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Attached is the International System of Units:

Convened in 1948 The Ninth International Conference on Weights and Measures made a decision, requiring the International Committee on Weights and Measures to create a simple and scientific practical unit system that can be used by all member countries of the metric convention organization. In 1954, the 10th International Conference on Weights and Measures decided to adopt the meter (m), kilogram (kg), second (s), ampere (A), Kelvin (K) and candela (cd) as the basic units. In 1960, the Eleventh International Conference on Weights and Measures decided to name the practical system of measurement with these six units as the "International System of Units" and stipulated that its symbol be "SI". Later, in 1974, the 14th International Congress of Weights and Measures decided to add the unit mole (mol) as the basic unit for the quantity of matter. Therefore, there are currently seven basic units in the International System of Units.

The International System of Units has two auxiliary units, radians and steradians.

SI derived units are derived from SI basic units according to definitions. There are many of them. Three categories are listed here: some SI derived units represented by SI basic units; SI derived units with special names. Unit; a portion of SI derived units expressed in SI auxiliary units.

Among them, there are a total of 19 SI export units with special names. There are 17 named after outstanding scientists, such as Newton, Pascal, Joule, etc., to commemorate their contributions in the field of this subject. At the same time, for convenience of expression, these derived units can also be combined with other units to represent other more complex derived units.

The International System of Units is the foundation and core of metrological research. In particular, the reproduction, preservation and value transfer of the seven basic units are the most fundamental research topics in metrology.

SI basic unit

Unit name unit name unit symbol

Length meter m

Mass kilogram kg

Time seconds s

Current ampere [ampere] A

Thermodynamic temperature open [irvin] K

Luminous intensity candela [dera] cd

Amount of substance mole [mol] mol

SI auxiliary unit

Name of the unit Unit name Unit symbol

Plane angle rad

Solid angle steradian sr

SI derived unit

Quantity name unit name unit symbol

Frequency Hertz [tz] Hz

Force; gravity Newton [ton] N

Pressure, pressure Pa [scal] Pa

Energy; work; thermal joule [ear] J

Power; radiant flux Watts [Special] W

Charge Coulomb [Lun] C

Potential; Voltage; Electromotive Force Volts [Special] V

Capacitance Far [Rad] F

Resistance Ohm [M] Ω

Conductance Siemens [Menzi] S

Magnetic Flux Weber [Both] Wb

Magnetic flux density, magnetic induction intensity special [SiLa] T

Inductance Henry [Li] H

Celsius temperature Celsius ℃

Light flux flow [Ming] lm < /p>

Illuminance lux [x] lx

Radioactivity Becquer [ler] Bq

Absorbed dose Gray [ray] Gy

Dose equivalent Sievert [Sv]

Definition of SI basic unit

Length: meter (m)

1. May 1790 by a French scientist A special committee formed by the United Nations recommended that one 40 millionth of the total length of the Earth's meridian passing through Paris be used as the unit of length - meter

2. The 11th International Congress of Weights and Measures in 1960: "The length of the meter It is equal to 1650763.73 times the wavelength of the radiation transitioning between the 2P10 and 5d1 energy levels of the krypton-86 atom in vacuum."

3. The 17th International Congress of Weights and Measures held in Paris in October 1983: "The meter is the length of the journey of light in a vacuum within the time interval of 1/299792458 seconds"

Mass: kilogram (kg)

The kilogram is defined as the mass of the international prototype of the kilogram.

Time: second (s)

In 1967, the 13th International Conference on Weights and Measures passed a resolution to adopt the following definition to replace the astronomical definition of the second: One second is cesium- The duration of the transition radiation between the two hyperfine energy levels of the 133 atom ground state is 9,192,631,770 cycles.

International Atomic Time is an international reference time scale based on the above definition of second and belongs to the International System of Units (SI).

Current: Ampere (A)

Ampere is a constant current, if it is maintained in two infinitely long parallel lines 1 meter apart in a vacuum, and the circular cross-section can be ignored In a straight wire, the force generated between the two wires is equal to 2×10-7 Newtons per meter of length. This definition was approved at the 9th CGPM in 1948, and at the 11th CGPM in 1960, the ampere was officially adopted as one of the basic units of the International System of Units. Ampere was named in honor of the French physicist A.-M. Ampere.

Thermodynamic temperature: Kelvin [Kelvin] (K)

Kelvin in English is Kelvin, abbreviated as Kelvin, the international code is K, the unit of thermodynamic temperature. Kelvin is one of the seven basic units in the International System of Units (SI). With absolute zero (0K) as the lowest temperature, the temperature of the triple point of water is stipulated as 273.16K. 1K is equal to 1/273.16 of the triple point temperature of water. The relationship between thermodynamic temperature T and the commonly used Celsius temperature t is T = t + 273.15, because the freezing point temperature of water is approximately equal to 273.15K, and the unit of thermodynamic temperature (K) is exactly the same as the unit of Celsius temperature (℃). . Kelvin was named in honor of the British physicist Lord Kelvin.

Luminous intensity: candela (cd)

Candela is the luminous intensity in a given direction of a light source that emits a monochromatic light with a frequency of 540 × 1012 Hz Radiation, and the radiation intensity in this direction is 1/683 watt per steradian.

The wavelength of 540×1012 Hz radiation in the definition is approximately 555nm, which is the wavelength that the human eye is most sensitive to.

Amount of substance: mole (mol)

A physical quantity indicating the number of particles that make up a substance (the amount of substance is a special noun, indivisible and omitted)

Mole is the unit of physical quantity of matter

According to scientific determination, the number of C atoms contained in 12 grams of 12C is 6.0220943×1023, represented by the symbol NA, which is called Avogadro’s constant

Avogadro’s constant (NA) approximate value 6.02×1023

Definition: Any substance containing Avogadro’s constant structural particles (about 6.02×1023), its substance The amount is 1 mol.

Definition of SI auxiliary units

Plane angle: radians (rad)

The central angle subtended by an arc whose length is the circumference of the circle (2∏r) is 2π radians, and the central angle subtended by an arc half the circumference of a circle is ∏ radians.

Solid angle: steradian (sr)

With the center of a sphere with radius r as the vertex, the spherical surface area corresponding to the expanded solid angle is r^2. The solid angle The size of is the sphericity.

Definition of SI derived units

Frequency: Hertz (Hz)

The frequency of a periodic process occurring within a time interval of 1 second, that is, 1Hz =1s^-1

Force; gravity: Newton [ton] (N)

The force that causes an object with a mass of one kilogram to produce an acceleration of 1 meter per square second, that is, 1N =1kg·m/s^2

Pressure, pressure: Pa[scal] (Pa)

Equal to 1 Newton per square meter, that is, 1Pa=1N/m

Energy; work; heat: Joule (J)

The work done when the point of action of 1 Newton force moves 1 meter in the direction of the force, that is, 1J=1N·m

Power; radiant flux watt [special] W

The power that produces 1 joule of energy within a time interval of 1 second, that is, 1W=1J/s

Charge: Coulomb (C)

The amount of electricity transported by one ampere of current in a time interval of 1 second, that is, 1C=1A·s

Potential; voltage; electromotive force: Volt [ter] (V)

In a wire flowing with a constant current of 1 ampere, if the power consumed between two points is 1 watt, the potential difference between the two points is 1 volt [ Special], that is, 1V=1W/A

Capacitance: Fara [Ra] (F)

When the capacitor is charged with 1 coulomb of electricity, a voltage of 1 volt appears between its two plates. Potential difference, that is, 1F=1C/V

Resistance: Ohm (Ω)

The resistance between two points of a conductor, when 1 is added between the two points When the potential difference is constant in volts, a current of 1 ampere is generated in the conductor, but there is no electromotive force in the conductor, that is, 1Ω=1V/A

Conductance: Siemens (S)

Conductance is numerically equal to the reciprocal of resistance, that is, 1S=1/Ω

Magnetic flux: Weber (Wb)

A physical quantity that characterizes the distribution of magnetic field.

The magnetic flux dΦB passing through the surface element dS somewhere in the magnetic field is defined as the product of the magnitude of the magnetic induction intensity B and the projection dScosθ of dS in the direction perpendicular to B, that is, 1Wb=1T·m^2

Magnetic flux Density, magnetic induction intensity: Tesla (T)

When a 1-meter-long wire perpendicular to the direction of the magnetic field passes through a current of 1 ampere, and the force exerted by the magnetic field is 1 Newton, the position of the energized wire The magnetic induction intensity at is 1 Tesla, that is, 1T=1N/(A·m)

Inductance: Henry (H)

The inductance of a closed loop, when When the current flowing through the circuit changes uniformly at a rate of 1 ampere per second, an electromotive force of 1 volt is generated in the loop, that is, 1H=1V·s/A

Celsius temperature: degrees Celsius (℃)

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The boiling point is set to 100 degrees, the freezing point is set to zero degrees, which is divided into one hundred equal parts, and one equal part is divided into one degree, that is, 1℃=1K-273.15

Luminous flux: lumen [light] ( lm)

A point light source with a luminous intensity of 1 candela (cd) emits a luminous flux of 1 lumen within a unit solid angle (1 steradian), that is, 1lm=1cd/sr

Illuminance: lux [x] (lx)

The illuminance of 1 lumen of luminous flux evenly distributed over an area of ??1 square meter is one lux, that is, 1lx=1lm/m^2

< p>Radioactive activity: Becquer [Ler] (Bq)

Equal to 1 activity per second, that is, 1Bq=1s^-1

Absorbed dose: Gray ](Gy)

Equal to the absorbed dose of 1 joule per kilogram, that is, 1Gy=1J/kg

Dose equivalent: Sievert (Sv)

Equal to the dose equivalent of 1 joule per kilogram, that is, 1Sv=1J/kg