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SCIENCE · INVESTIGATE AND EXPLAIN

Compare path integrals with endpoint energy

Integrate field components along each displacement and test path independence.

Learning outcome: Change B through −2, 0 and +2 while holding A fixed. Predict segment integrals, compare both cumulative curves, and independently integrate the straight path. Reverse the path and explain which signs reverse. Do not interpret the displayed segment parameter as physical distance or travel time.

Starting recap

Keep source normalization, potential reference, signed energy and evidence independence explicit.

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Try

For A = 2 and B = 1, delta V = 13 V. Horizontal-first work per charge is −8 − 5 = −13 J/C; vertical-first gives −3 − 10 = −13 J/C. For q = −2 nC, field work is +26 nJ and delta U = −26 nJ.

Open the experiment

Predict

Two different paths connect the same endpoints in this static electrostatic field. Which quantity must agree?

Experiment

Change B through −2, 0 and +2 while holding A fixed. Predict segment integrals, compare both cumulative curves, and independently integrate the straight path. Reverse the path and explain which signs reverse. Do not interpret the displayed segment parameter as physical distance or travel time.

Compare two paths through one electrostatic field

Worked teaching model · synthetic values · V = Ax² + Bxy + 3y² in SI units. Static field is negative spatial gradient. Compare paths from (0,0) to (2,1) m, one horizontal then vertical and one vertical then horizontal, plus straight path. Work per positive unit charge is integral E dot dr.

Reset keeps your prediction, captures and practice history.

Cumulative horizontal-first integral

integral E dot dr (J/C)path parameter 0..2 (not distance)020-13

Axes rescale independently. Curves join sampled coordinates; a joining segment is not additional measured evidence. Read physical units rather than screen angles or apparent slopes.

Cumulative horizontal-first integral: numerical coordinates
path parameter 0..2 (not distance)integral E dot dr (J/C)
00
0.0333333-0.00888889
0.0666667-0.0355556
0.1-0.08
0.133333-0.142222
0.166667-0.222222
0.2-0.32
0.233333-0.435556
0.266667-0.568889
0.3-0.72
0.333333-0.888889
0.366667-1.07556
0.4-1.28
0.433333-1.50222
0.466667-1.74222
0.5-2
0.533333-2.27556
0.566667-2.56889
0.6-2.88
0.633333-3.20889
0.666667-3.55556
0.7-3.92
0.733333-4.30222
0.766667-4.70222
0.8-5.12
0.833333-5.55556
0.866667-6.00889
0.9-6.48
0.933333-6.96889
0.966667-7.47556
1-8
1.03333-8.07
1.06667-8.14667
1.1-8.23
1.13333-8.32
1.16667-8.41667
1.2-8.52
1.23333-8.63
1.26667-8.74667
1.3-8.87
1.33333-9
1.36667-9.13667
1.4-9.28
1.43333-9.43
1.46667-9.58667
1.5-9.75
1.53333-9.92
1.56667-10.0967
1.6-10.28
1.63333-10.47
1.66667-10.6667
1.7-10.87
1.73333-11.08
1.76667-11.2967
1.8-11.52
1.83333-11.75
1.86667-11.9867
1.9-12.23
1.93333-12.48
1.96667-12.7367
2-13

Cumulative vertical-first integral

integral E dot dr (J/C)path parameter 0..2 (not distance)020-13

Axes rescale independently. Curves join sampled coordinates; a joining segment is not additional measured evidence. Read physical units rather than screen angles or apparent slopes.

Cumulative vertical-first integral: numerical coordinates
path parameter 0..2 (not distance)integral E dot dr (J/C)
00
0.0333333-0.00333333
0.0666667-0.0133333
0.1-0.03
0.133333-0.0533333
0.166667-0.0833333
0.2-0.12
0.233333-0.163333
0.266667-0.213333
0.3-0.27
0.333333-0.333333
0.366667-0.403333
0.4-0.48
0.433333-0.563333
0.466667-0.653333
0.5-0.75
0.533333-0.853333
0.566667-0.963333
0.6-1.08
0.633333-1.20333
0.666667-1.33333
0.7-1.47
0.733333-1.61333
0.766667-1.76333
0.8-1.92
0.833333-2.08333
0.866667-2.25333
0.9-2.43
0.933333-2.61333
0.966667-2.80333
1-3
1.03333-3.07556
1.06667-3.16889
1.1-3.28
1.13333-3.40889
1.16667-3.55556
1.2-3.72
1.23333-3.90222
1.26667-4.10222
1.3-4.32
1.33333-4.55556
1.36667-4.80889
1.4-5.08
1.43333-5.36889
1.46667-5.67556
1.5-6
1.53333-6.34222
1.56667-6.70222
1.6-7.08
1.63333-7.47556
1.66667-7.88889
1.7-8.32
1.73333-8.76889
1.76667-9.23556
1.8-9.72
1.83333-10.2222
1.86667-10.7422
1.9-11.28
1.93333-11.8356
1.96667-12.4089
2-13
Calculated values under the declared model
QuantityValueUnit
Endpoint potential difference13V
Horizontal-first path segment 1 work per charge-8J/C
Horizontal-first path segment 2 work per charge-5J/C
Vertical-first path segment 1 work per charge-3J/C
Vertical-first path segment 2 work per charge-10J/C
Total work per charge on either path-13J/C
Closed-loop work per charge0J/C

The segments differ, but the two complete electrostatic path integrals agree.

Integrate the field component along each displacement, not the field magnitude times path length. For the straight path (x,y) = (2t,t), E dot dr/dt = −(8A + 4B + 6)t, giving the same endpoint result. Time-dependent induction later requires revisiting the electrostatic premise.

Derive before checking. Retain contrasting captures and explain one assumption that could fail; calculated evidence is not actual laboratory work.

The segments differ, but the two complete electrostatic path integrals agree.

Integrate the field component along each displacement, not the field magnitude times path length. For the straight path (x,y) = (2t,t), E dot dr/dt = −(8A + 4B + 6)t, giving the same endpoint result. Time-dependent induction later requires revisiting the electrostatic premise.

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Derive the field before selecting a path

For V = Ax² + Bxy + 3y², E = (−2Ax − By, −Bx − 6y). The electrostatic work per charge is integral E dot dr = −delta V. This result uses a static conservative field. A changing magnetic environment later can require a different account; it is not justified to impose electrostatic path independence on every electric field.

Keep segment limits and directions

From (0,0) to (2,1), horizontal-first work per charge is −4A on y = 0, then −2B − 3 on x = 2. Vertical-first gives −3 on x = 0, then −4A − 2B on y = 1. Both totals equal −4A − 2B − 3. The paths have different intermediate accumulations, not different final electrostatic work.

Check a third parameterization

Along (x,y) = (2t,t), 0 ≤ t ≤ 1, dr/dt = (2,1). The dot product is −(8A + 4B + 6)t; integrating gives the same total. Integrating the field magnitude instead would discard signs and perpendicular components. Joining one forward path to the reverse of another produces zero closed-loop electrostatic work.

Worked original case

For A = 2 and B = 1, delta V = 13 V. Horizontal-first work per charge is −8 − 5 = −13 J/C; vertical-first gives −3 − 10 = −13 J/C. For q = −2 nC, field work is +26 nJ and delta U = −26 nJ.

Investigation

Change B through −2, 0 and +2 while holding A fixed. Predict segment integrals, compare both cumulative curves, and independently integrate the straight path. Reverse the path and explain which signs reverse. Do not interpret the displayed segment parameter as physical distance or travel time.

Changed-case practice

Try a new practice case

Set A = 3 and B = −1. What is field work per positive unit charge from (0,0) to (2,1), in J/C?

This public, unsaved check is not a secure assessment. Explain the source integral, symmetry or charge boundary in the retained course evidence workspace.

Sources and evidence boundary

Original teaching and cases checked 30 October 2026 against the current official framework, Unit 9 and OpenStax electric potential. All records are supplied or generated, not measured by a learner. No physical charging, battery connection, high-voltage equipment or particle experiment is requested. Retain predictions, derivations and critique in the course evidence workspace; public feedback is not independent mastery or performed laboratory time.

Apply

Two different paths connect the same endpoints in this static electrostatic field. Which quantity must agree?

Public practice checks a specific claim. It does not establish independent mastery.

Which reference, source geometry or evidence-independence assumption limits your inference?

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