NEB Class 11 • Physics • Focused Revision

Electric Potential, Potential Difference & Potential Energy Study Guide: NEB 11 Physics

Build a reliable sign-and-energy method: separate V from U, define endpoints, add scalar point potentials and connect potential maps to electric fields.

Seven-session revision sequence
Work, voltage and energy sign drills
Point potentials, equipotentials and timed test

Electric field crosses equipotentials at right angles.

Revision boundary

Study endpoints, signs and reference choices

Use the CDC secondary curriculum and CDC Physics Grade 11 page. Read the paired concept guide and OpenStax potential-difference treatment.

Every problem should name initial point, final point, source configuration, reference and sign of the moved charge.

Knowledge map

Use four linked representations

Scalar landscape

V at each point relative to a chosen zero.

Energy

U=qV and ΔU=qΔV.

Work

W_field=−ΔU.

Field map

E points across equipotentials toward lower V.

Do not merge the landscape and traveller: V is set by sources; U depends on the charge placed in that landscape.

Seven sessions

A spaced potential-and-energy plan

Session	Focus	Exit evidence
1	Definitions and units	Twelve classification cards
2	ΔV, ΔU and work signs	Eight endpoint problems
3	Point-charge potentials	Six scalar superpositions
4	Uniform field relation	Five plate calculations
5	Equipotential maps	Six contour interpretations
6	Energy conservation and eV	Six particle problems
7	Timed integrated set	80% without repeated sign error

Sign routine

Write final minus initial before substitution

Write ΔV=V_f−V_i.
Write the sign of moved q.
Calculate ΔU=qΔV.
Use W_field=−ΔU.
If only electrostatic force acts, set ΔK=−ΔU.
Translate the result into energy gain or loss.

Same voltage, opposite charges

Across ΔV=−50 V, +3 μC gives ΔU=−150 μJ and field work +150 μJ. A −3 μC charge gives ΔU=+150 μJ and field work −150 μJ.

Calculation practice

Switch between scalar potential and vector field

Potential from three sources

At P, +2 nC is 0.10 m away, −3 nC is 0.20 m away and +1 nC is 0.40 m away. V=k(2e−9/0.10−3e−9/0.20+1e−9/0.40)≈67.4 V.

Placed-charge energy

A −4 nC charge placed at V=67.4 V has U=qV≈−2.70×10⁻⁷ J relative to the same reference.

Uniform field

Moving 4.0 cm along a 1.5×10⁴ N/C field gives ΔV=−Ed=−600 V. Moving perpendicular gives ΔV=0.

Electron volt

3.0 keV=3000 eV≈4.81×10⁻¹⁶ J. The prefix belongs to the energy unit, not charge.

Equipotential rehearsal

Draw E arrows from contour spacing

At five points on a map, draw E perpendicular to the contour toward lower labelled V. Rank field strength by ΔV divided by perpendicular spacing. Moving along one contour requires zero electrostatic work; moving between contours changes U by qΔV.

Nonuniform map

Contours 10 V apart are 2 mm apart near A and 8 mm apart near B. The average local field estimate is about four times larger near A, assuming distances are measured perpendicular to contours.

Use PhET Charges and Fields only after drawing predictions.

Error log

Repair the first wrong definition

Error	Code	Repair
Used V=qU	definition	Write U=qV
Used initial minus final	endpoints	Label A→B
Vector-added potential	scalar	Add signed kQ/r
Equated V=0 with E=0	relationship	Draw dipole midpoint
Called eV a voltage	unit	Convert to joules

Thirty-five minute checkpoint

Integrated readiness tasks

Distinguish V, ΔV and U.
Solve positive/negative charge work problems.
Add three point-charge potentials.
Compare V and E at a dipole midpoint.
Use ΔV=−Ed in a plate field.
Convert eV and joules.
Use energy conservation for a charged particle.
Interpret an equipotential map.

Reference and endpoints are stated.
Potential is scalar.
Moved-charge sign is visible.
Field work has the opposite sign to ΔU.
Equipotential spacing is measured perpendicularly.
Every result has an energy interpretation.

For online or physical NEB tuition, call 9846662070.

Frequently asked questions

Questions about studying potential and energy

What should I write first?

Write the initial and final points, ΔV=Vf−Vi, and the sign of the moved charge.

Why is potential easier to add than field?

Potential is scalar, so point-source contributions add algebraically; field requires vector components.

How do I remember work signs?

The electric field does positive work when electric potential energy decreases: Wfield=−ΔU.

How do equipotentials help?

Their labels show ΔV, their tangent path has zero work, and E crosses them toward lower potential.

What score shows readiness?

Aim for 80% on a fresh set with no repeated endpoint, charge-sign, scalar or unit error.

Where can I get potential tuition?

Call 9846662070 for current online or physical NEB tuition options and fees.

References and next steps

Sources and related study guides

Continue to Capacitors and revisit Electric Field Study Guide. Curriculum scope and sources were checked on 2 August 2026; follow current CDC, NEB and college instructions if requirements change.

Transfer workbook

Five sign and reference drills

Reference: changing zero shifts all V values by a constant but leaves ΔV and measurable work unchanged. Negative charge: higher V can mean lower U. Scalar cancellation: V may cancel where E does not. Endpoint reversal: reversing A→B changes signs of ΔV, ΔU and field work. Uniform field: only displacement parallel to E changes V.

Reference shift

If V_A=20 V and V_B=−10 V, ΔV=−30 V. Adding 100 V to the reference makes them 120 V and 90 V, but ΔV remains −30 V.

Write two versions of each problem, one with +q and one with −q. Highlight which quantities belong to sources and which change with the traveller.

Worked revision workbook

Seven problems that change the relationship

1. Endpoint reversal

A +5 μC charge moves A→B where V_A=80 V and V_B=20 V. ΔV=−60 V, ΔU=−300 μJ and W_field=+300 μJ. Reversing B→A changes all three signs.

2. Negative traveller

For q=−5 μC on the same A→B path, ΔU=+300 μJ and field work is −300 μJ. Source potentials do not change because the traveller sign changed.

3. Scalar cancellation

At a point equidistant from +4 nC and −1 nC, V=3k nC/r, not zero. For field, direction and components must be calculated separately.

4. Zero-potential location

Between +4Q at x=0 and −Q at x=d, set 4/x=1/(d−x), giving x=4d/5 from +4Q. This potential-zero point is not generally a field-zero point.

5. Uniform plate map

Contours 100 V apart and 5.0 mm apart give E≈2.0×10⁴ V/m perpendicular toward lower V. Moving 2.0 cm along E changes potential by about −400 V.

6. Electron energy

An electron accelerated through a 2.5 kV rise gains 2.5 keV of kinetic energy if released appropriately. In joules this is 2.5×10³×1.602×10⁻¹⁹≈4.01×10⁻¹⁶ J.

7. Three-charge energy

Write all three pair terms once. Predict which attractive negative terms and repulsive positive terms dominate before summing.

Timed oral defence

Explain each answer in the order: source landscape, reference, endpoints, traveller sign, energy change and work. Then draw the corresponding field direction. If the field and potential statements disagree, inspect the negative gradient and charge sign rather than changing the final answer by intuition.

Retest four problems after 48 hours with endpoints or charge signs changed. Keep an error code for reference, endpoints, scalar sum, traveller sign, work sign, unit and model limit.

Timed mixed paper

Twenty-five minute transfer test

Find work moving +3 μC from 40 V to −20 V.
Repeat for −3 μC and compare signs.
Find V from +2 nC and −5 nC at unequal distances.
Locate a zero-potential point between unequal opposite charges.
Find E from a linear V–x graph.
Convert 4.5 keV to joules.
Find speed from electrostatic energy gain.
Explain why an equipotential path has zero field work.

Mark one point each for reference, endpoints, traveller sign, scalar sum, work sign, unit and interpretation. A correct magnitude without endpoint language is incomplete.

After marking, reverse each path and predict changes without recalculation. Shift every potential label by +100 V and verify that differences and work remain unchanged. Finally compare a zero-V point with a zero-E point using one dipole diagram.

Keep a three-column record: error, repaired rule and contrast problem. Retest after two days from an empty page. Use the point-source formula only when the source geometry supports it and state the zero-at-infinity reference.

Weekly transfer: draw a V–x graph with flat, rising and falling regions. Infer E in each region from the negative slope, then place positive and negative charges and predict force directions. Add a vertical shift to the whole graph and explain why E is unchanged. Finally choose two points and calculate ΔV, ΔU and field work for both charge signs. This single page tests reference, derivative, endpoint and traveller concepts together.

Keep every corrected attempt for later comparison.

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