EMG-21

Point-charge field

Coulomb field of a point.

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GoverningPoint-charge field

Governing equation

E=kq/r^2

$r \in \left[0.02, 2\right]$

where

q: q (nC)
r: r (m)
E: Point-charge field (N/C)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

E=kq/r^2

$r \in \left[0.02, 2\right]$

$r = 0.02$ $E = 45000$

Along the curve

②

Domain of the variable — blue

r_{\min} = 0.02,\quad r_{\max} = 2

$r \in \left[0.02, 2\right]$

$r = 0.02$ $r = 0.02$

Along the curve

③

Response curve — green

E=kq/r^2

$r \in \left[0.02, 2\right]$

$r = 0.02$ $E = 45000$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}E}{\mathrm{d}r}

$r \in \left[0.02, 2\right]$

$r = 0.032$ $E^{\prime} = -1.45\times 10^{6}$

Along the curve

Lecture brief

Historical brief

Coulomb, Gauss, Ampère, Faraday and Maxwell (1861–65) unified charge, current and light. The lab computes fields, induction, Poynting flux and the electromagnetic wave in SI. This sheet (EMG-21 — Point-charge field) is the form associated with Point-charge field. Working symbols: $q$ , $r$ $\rightarrow$ $E$ . Coulomb field of a point. Pedagogical SI sheet with a live model and a swept parameter.

Purpose

Purpose: compute

E

from

q

r

in Electromagnetism via

E=kq/r^2

Coulomb field of a point. Use it when a real electromagnetism question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

q = 2.000\,\mathrm{nC}

r = 0.200\,\mathrm{m}

, the governing relation

E=kq/r^2

yields

E = 450.000\,\mathrm{N/C}

. One governing identity, SI units, a single sweep on the sheet. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

q q2 nCr r0.2 m

Outputs

Point-charge field E450.000 N/C

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Narration of this film

One governing identity, SI units, a single sweep on the sheet.

Coulomb field of a point. Pedagogical SI sheet with a live model and a swept parameter.

Reading speed

Watch on YouTube