Electrostatic Fields Lab
Electrical Engineering I · Module 92315 · Chapter 1
Predict first, then watch. Every experiment starts with challenges: choose what you expect and how sure you are, and the simulation shows what really happens. When the challenges are done, the sandbox opens.
How the lab works
- Predict. Pick an answer before anything moves. A wrong guess still helps you learn, as long as you commit to it.
- Rate how sure you are. Being sure and wrong is the most useful thing to find out; those answers are listed under Your results.
- Watch the reveal. The simulation plays the true result, keeps your guess on screen, and links the matching section of the guide.
- Explore. Finishing an experiment opens its sandbox and ticks a lab skill on the hub.
1.2–1.9 Point charges: field, potential and work
Point charges, the field they make and the work it takes to move a probe charge through it. The picture is a flat slice through the real three-dimensional field, so it follows the 1/r2 law of the notes.
Analogy: a hiking map
Potential is altitude. Equipotential lines are the contour lines on the map. The field points straight downhill, and it is strongest where contour lines bunch together (a steep slope). Voltage is the height difference between two places.
| Picture | Electrostatics |
|---|---|
| altitude above sea level | potential φ |
| sea level | reference point (earth or ∞) |
| contour lines | equipotential lines |
| steepest downhill direction | field E |
| height gain between huts | voltage U |
Holds: the height gained from hut A to hut B is the same by the short steep path or the long gentle one. Walking a loop back to the start gains nothing. Moving the “sea level” changes every altitude but no height difference.
Breaks: everything rolls downhill on a real hill. A negative charge “rolls uphill” in φ, because the force on it is −|Q|E.
Grid: 5 cm · dashed: equipotentials · lines: field lines
1.10 Gauss’s law: a charged cylinder
The worked example from 1.10: an infinitely long, uniformly charged cylinder, seen end-on. Move the coaxial Gaussian surface and watch how much charge it encloses and what that does to D.
Analogy: a light bulb in the dark
A bulb sends out a fixed amount of light. Wrap it in an imaginary closed surface: all the light passes through it, whatever its size or shape. For a long tube light the same holds for a coaxial sleeve: the light through it depends only on the length of tube inside.
| Picture | Electrostatics |
|---|---|
| power of the bulb | charge Q inside |
| light arriving per m² | flux density D |
| total light through the surface | flux Ψ = Q |
| a second bulb inside adds its light | superposition |
Holds: total through any closed surface = what is inside, independent of the surface’s size or shape. A bulb outside adds nothing in total: its light goes in one side and out the other. Same for a charge outside a Gaussian surface.
Breaks: light really travels and carries energy away. In electrostatics nothing flows; “flux” is only a count of field lines, a historical name. And light has no “negative bulb”, while a negative charge is exactly where field lines end.
1.11 Interface conditions: field refraction
A uniform field crossing the flat boundary between two media. The bars compare both sides: which part keeps its value, which one jumps, and how that bends the field lines.
Analogy: light bending into water
A light ray entering water bends at the surface; the notes make the same comparison. Field lines bend at a jump in ε, and the amount follows from which component must stay continuous.
| Picture | Electrostatics |
|---|---|
| ray | field line |
| refractive index | permittivity ε |
| angle to the normal | α1, α2 |
Holds: a direction change at a boundary, set by a material property on each side, and no bending at normal incidence (α1 = 0).
Breaks: light obeys Snell’s law with sines and the refractive index; the field obeys a tangent law with ε. And at a water surface part of the light is reflected; the field has no reflected part.
1.12–1.14 Plate capacitor: gap, dielectric and energy
An ideal plate capacitor, drawn to scale. Field-line density shows E, the tint shows the energy density, and the signs on the plates grow with the charge. Watch what stays fixed: with the battery connected it is U, with it disconnected it is Q.
Analogy: a water tank filled from below
Pump water into a tank through a pipe at the bottom. The water level rises with the volume inside; a wider tank rises less for the same volume. Each new litre must be pushed against the pressure of the water already there.
| Picture | Electrostatics |
|---|---|
| volume of water | charge Q |
| water level (pressure) | voltage U |
| tank’s floor area | capacitance C |
| volume = area × level | Q = C U |
| energy ½ρgAh² | energy ½C U2 |
Holds: Q = C U, the ½ in the energy (the first water was lifted less), and tanks side by side at the same level add their areas (parallel).
Breaks: a capacitor holds +Q and −Q, so its total charge is zero; a tank really holds water. Series capacitors have no clean tank picture. The notes also use a spring (C ↔ 1/spring constant, U ↔ force), which carries the energy formula equally well.
1.13 Capacitor networks: series and parallel
Two or three capacitors on one source. The bars show each capacitor's voltage and charge: in series look for what they share, in parallel for what they split.
Your results
Personal study lab based on the supplied Electrical Engineering I Chapter 1 notes (WS 2026/27). Simulations use the notes' formulas and constants; check anything exam-relevant against the official course materials. Not an official FAU publication. Made by Thanate Amornjiraporn (Focus).