Magnetic current field

Содержание и основные понятия

The electric current creates a magnetic field; its direction around the direct conductor is defined by the right hand rule, and the field painting is examined by magnetic arrow or iron sawdust.
GEF · Grade 8
PIF · Baseline
Interactive model
Magnetic field
magnetic line
solenoid
Right-hand rule
01
The physical picture
What happens and what boundaries the model has.
Main message
The electric current creates a magnetic field; its direction around the direct conductor is defined by the right hand rule, and the field painting is examined by magnetic arrow or iron sawdust.
Magnetic lines are closed and have no beginning or end.
The field is reinforced by increasing current and approaching the conductor.
In the solenoid, the fields of turns fold, creating an almost homogeneous field inside.
How to reason
First, name the system and the interaction, then select the values, and only then write down the law. The formula works within the model's assumptions.
02
Laws and values
Symbols should be read as a relationship of values, not as a recipe for substitution.
B
∼
I
r
B\sim\frac{I}{r}
B
∼
r
I
​
the quality of the conductor field
B
∼
N
I
l
B\sim\frac{NI}{l}
B
∼
l
N
I
​
Long coil field
Review of the situation
If you change the direction of the current in the coil, its northern and southern magnetic poles will change.
04
Links and application
In the real world
If you change the direction of the current in the coil, its northern and southern magnetic poles will change.
Model verification
Compare the prediction with observation, evaluate the units, the order of magnitude and the influence of the factors not taken into account. Disparity does not always mean an error of law: often idealization is no longer sufficient.
C
What needs to be understood
Outcome 1
Explain the physical meaning of the topic "Magnetic current field" through the model, not just the formula.
Outcome 2
To distinguish and correctly use terms: magnetic field, magnetic line, solenoid.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
Magnetic field
Composing an electromagnetic field that operates on moving charges and magnetic moments.
magnetic line
An imaginary line to which the tangent matches the direction of the magnetic induction vector.
solenoid
A long cylindrical coil that creates an almost homogeneous magnetic field in the current.
Right-hand rule
A mnemonic rule to determine the direction of magnetic current lines or induction current.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
B
∼
I
r
B\sim\frac{I}{r}
B
∼
r
I
​
empirical law
The quality of the field of wire.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
B
∼
I
B\sim I
B
∼
I
The measurements near the straight wire shall be fitted with magnetic field reinforcement proportional to current.
B
∼
1
r
B\sim\frac{1}{r}
B
∼
r
1
​
The same measurements show the inverse proportionality of the field of distance from the long wire.
B
∼
I
r
B\sim\frac{I}{r}
B
∼
r
I
​
The proportionality mark emphasizes that the factor depending on the environment and geometry is not recorded here.
Conditions:
A very long straight thin wire, an observation point far from its end, a homogeneous linear environment; a high-quality dependence.
Monitoring:
The proportionality shall be verified; the dimension of full equality shall restore the factor omitted.
B
∼
N
I
l
B\sim\frac{NI}{l}
B
∼
l
N
I
​
model effect
Long coil field.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
n
=
N
l
n=\frac{N}{l}
n
=
l
N
​
The density of the long coil is equal to the number of turns per unit length.
B
∼
n
I
B\sim nI
B
∼
n
I
Fields of close turns inside the long solenoid are folded, so the field is proportional to the density of the turns and current.
B
∼
N
I
l
B\sim\frac{NI}{l}
B
∼
l
N
I
​
The replacement of n with N/l gives a qualitative relationship to the coil field.
Conditions:
Long, tight-wrapped solenoid away from the creeks, the same current in all turns, linear heart, no environmental factor specified.
Monitoring:
The proportionality shall be verified; the dimension of full equality shall restore the factor omitted.
!
Model boundaries and typical errors
Error: Forget model condition
The key condition of this topic is that the magnetic lines are closed and have no beginning or end.
How to Check the Mind
The field is reinforced by increasing current and approaching the conductor. Then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
Magnetic current field
The electric current creates a magnetic field; its direction around the direct conductor is defined by the right hand rule, and the field painting is examined by magnetic arrow or iron sawdust.
Magnetic lines are closed and have no beginning or end.
The field is reinforced by increasing current and approaching the conductor.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.