Current and voltage

Содержание и основные понятия

The electric current is the directional movement of charged particles, which requires free carriers, electric field, and a closed circuit.
GEF · Grade 8
PIF · Baseline
Interactive model
Electrical current
current
voltage
current source
01
The physical picture
What happens and what boundaries the model has.
Main message
The electric current is the directional movement of charged particles, which requires free carriers, electric field, and a closed circuit.
The current force is equal to the charge passing through the cross section per unit of time.
The voltage characterizes the field's transport of a single charge.
The amperometer is set in sequence, and the voltmeter is parallel to the section.
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.
I
=
q
t
I=\frac{q}{t}
I
=
t
q
​
current
U
=
A
q
U=\frac{A}{q}
U
=
q
A
​
Electrical voltage
Review of the situation
The current of 0.5 A means that the cross section of the conductor passes through a charge of 0.5 Kl every second.
04
Links and application
In the real world
The current of 0.5 A means that the cross section of the conductor passes through a charge of 0.5 Kl every second.
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 "Took and voltage" through the model, not just through the formula.
Outcome 2
Distinguish and correctly use terms: electric current, current, voltage.
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.
Electrical current
Ordered movement of electrically charged particles.
current
A charge passing through the cross-section of the conductor per unit of time.
voltage
The difference between the capabilities of the two points is equal to the field's work in carrying the single charge.
current source
A device in which the external forces separate the charges and maintain the different capabilities.
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.
I
=
q
t
I=\frac{q}{t}
I
=
t
q
​
definition
The power of current.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
I
ср
=
Δ
q
Δ
t
I_{\text{ср}}=\frac{\Delta q}{\Delta t}
I
cf
​
=
Δ
t
Δ
q
​
The average current shall be introduced as a charge passing through the cross section of the conductor per unit of time.
I
=
q
t
I=\frac{q}{t}
I
=
t
q
​
For constant current, the charge q passes over the t interval, so the ratio does not depend on the choice of the interval.
Conditions:
The non-addition formula refers to DC; q is the charge that passed through the selected section over time t > 0.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
U
=
A
q
U=\frac{A}{q}
U
=
q
A
​
definition
Electrical voltage.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
A
∼
q
A\sim q
A
∼
q
The electrical field is proportional to the charge value when the charge is carried between the two points.
U
=
A
q
U=\frac{A}{q}
U
=
q
A
​
The voltage shall be applied as a field per positive charge unit.
Conditions:
Consideration shall be given to the transfer of the charge between the two specified electrostatic field points or the chain section; q × 0, the operating mark is aligned with the direction of transport.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
!
Model boundaries and typical errors
Error: Forget model condition
The key condition of this topic is that the current is equal to the charge going through the cross section per unit of time.
How to Check the Mind
The voltage characterizes the field's transport of a single charge. Then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
Current and voltage
The electric current is the directional movement of charged particles, which requires free carriers, electric field, and a closed circuit.
The current force is equal to the charge passing through the cross section per unit of time.
The voltage characterizes the field's transport of a single charge.
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.