NEB Class 11 • Physics • Focused Revision

Electric Field Study Guide: NEB 11 Physics

Study electric fields by separating source, point and probe; predict directions before arithmetic; and use symmetry, vector components and field-line rules as independent checks.

Seven-session field revision sequence
Point-charge and superposition drills
Field-line, conductor and simulation checks

The field direction is defined for a positive test charge.

Revision boundary

Use three independent checks

Follow the CDC secondary curriculum and CDC Physics Grade 11 page. Study the paired Electric Field concept guide and compare it with OpenStax University Physics.

For every answer check: source-to-point directions, vector component sum and field-line or symmetry picture. Agreement is stronger than trusting one memorised sign.

Representation map

Keep source, field and force distinct

Sources

Charges and their positions create E.

Field point

The coordinate where E is evaluated.

Probe force

F=qE after a charge is placed.

Visual map

Vectors and field lines represent direction and relative strength.

Write the field without a test-charge factor. Only after E is known should you multiply by the placed charge and reverse the force direction for negative q.

Seven sessions

A spaced electric-field sequence

Session	Focus	Exit evidence
1	Definition, units, direction	Ten source–point arrows
2	Point-charge magnitude	Eight SI calculations
3	Collinear superposition	Five sign-safe problems
4	Two-dimensional components	Four vector maps
5	Field lines and symmetry	Six sketches with explanations
6	Conductors and uniform fields	Application cards
7	Timed integrated set	80% without repeated direction error

Use 55-minute sessions: closed-book arrows, correction, mixed calculations, then error logging. Repeat difficult vector maps after one, three and seven days.

Vector workflow

At each point, calculate one source at a time

Circle field point P.
Draw radial direction from every source.
Choose away from + and toward −.
Calculate k|Q|/r² using that source’s distance.
Resolve into x and y components.
Add and convert to magnitude–angle form.

Unequal like charges and zero field

+4Q at x=0 and +Q at x=d have a zero-field point between them. Set 4/x²=1/(d−x)², so 2/x=1/(d−x), giving x=2d/3 from +4Q, or d/3 from +Q. The point is closer to the smaller source.

Symmetric off-axis point

Equal positive charges at (±a,0) produce equal fields at (0,y). Horizontal components cancel and vertical components add: E_y=2kQy/(a²+y²)^3/2, pointing upward for y>0.

Field-line rehearsal

Draw rules, then explain why they exist

Start at + or infinity; end at − or infinity.
Arrow tangent gives E.
Density represents relative magnitude.
Line count represents relative source magnitude by convention.
No crossing because one point cannot have two E directions.
No closed electrostatic field-line loops.

Practise a single + charge, single − charge, dipole, equal like pair, unequal opposite pair and nearly uniform parallel-plate field. Under each drawing, mark one point and add the local E arrow tangent to the line.

Error correction

Repair the earliest model decision

Error	Code	Repair task
Field arrow follows negative test force	definition	Use positive probe first
Included q in source field	source/probe	Calculate E, then F
Used one common r	geometry	Label each source–P distance
Added magnitudes only	vector	Resolve components
Crossed field lines	representation	Check tangent uniqueness

Retest the same code with different signs or a rotated diagram after 48 hours. The goal is transfer, not recognising a stored page layout.

Simulation study

Use predict–observe–explain, not screen copying

In PhET Charges and Fields, place one positive source and predict four equal-radius vectors. Add a negative source and predict the midpoint before enabling field displays. Move one source and explain changes with direction, inverse-square distance and superposition.

Record one disagreement between prediction and display. Decide whether the cause was sign, distance, vector addition or screen-scale reading. A simulation is an ideal model; a physical probe can disturb charge and has finite resolution.

Forty-minute checkpoint

Integrated readiness tasks

Define field and distinguish it from force.
Calculate E from one positive and one negative source.
Find force on positive and negative test charges.
Solve like- and unlike-charge midpoint problems.
Find a zero-field point for unequal like sources.
Solve an off-axis symmetric pair.
Draw five field-line patterns.
Explain conductor equilibrium and shielding.
Critique a simulation as experimental evidence.

Point P and every source are labelled.
Direction is predicted before magnitude.
Fields, not charges, are vector-added.
Negative test charge reverses force only.
Symmetry is stated explicitly.
Field lines remain a representation.

For online or physical NEB tuition, call 9846662070.

Frequently asked questions

Questions about studying electric fields

What should I draw first?

Mark the field point and draw one away/toward arrow for each source before writing any magnitude.

How do I know where fields cancel?

Directions must oppose and magnitudes must be equal. Use sign reasoning to choose a possible region before solving distances.

Why separate E and F?

E belongs to the source configuration; F also depends on the placed charge and reverses for a negative charge.

How do I practise field lines?

Draw six standard patterns from memory, then add a tangent vector and relative-density explanation at chosen points.

What score shows readiness?

Aim for 80% on a fresh mixed set with no repeated source/probe, distance, vector or field-line error.

Where can I get electric-field tuition?

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

References and next steps

Sources and related study guides

Use the Electric Field Practice Set and revisit Electric Charges Study Guide for Coulomb foundations. Curriculum scope and sources were checked on 2 August 2026; follow current CDC, NEB and college instructions if requirements change.

Symmetry workbook

Predict cancellation before calculation

For a pair symmetric about an axis, match source elements in pairs. Decide which components cancel and which add. Equal like charges on a perpendicular bisector cancel horizontal components and add perpendicular components; a dipole reverses that pattern.

Limiting checks

Very far from two equal charges, the system resembles a point source with total charge 2Q for leading-order field. Very far from a +Q/−Q dipole, net charge is zero and the field decreases faster than 1/r². These limits check whether a derived expression is plausible.

Create four cards: midpoint of like pair, midpoint of unlike pair, perpendicular bisector of like pair and perpendicular bisector of dipole. Draw arrows before reading any equations and explain the symmetry in one sentence.

Transfer workbook

Five situations that prevent formula matching

1. Negative probe

A field at P points east. Placing a negative charge produces westward force. The field does not reverse because the source arrangement did not change.

2. Zero field, nonzero sources

At the midpoint of equal positive charges, contributions cancel. Move slightly toward one source and its inverse-square contribution becomes larger, so cancellation is lost.

3. Impossible zero region

Between +Q and −2Q, both fields point toward the negative source, so no zero lies between them. Search outside on the side of the smaller magnitude +Q before solving.

4. Uniform-field force balance

A charged object at rest between plates still experiences electric force if another force balances it. Write ΣF=0 rather than F_electric=0.

5. Field-line claim

Closer drawn lines indicate stronger field only within a consistent diagram whose line count convention is controlled. Do not compare arbitrary drawings made with different numbers of lines.

Oral explanation test

For each situation, speak in this order: source configuration, field direction, magnitude relation, placed-charge force, and limiting assumption. Record one response and replace vague words such as “pull” or “cancelled charge” with vector language.

Finish with a 30-minute shuffled set containing one single source, one collinear pair, one off-axis symmetric pair, one field-line sketch, one conductor explanation and one uniform-field force balance. Mark the first decision separately from arithmetic.

Weekly transfer: choose a new three-charge diagram and predict the resultant quadrant without calculation. Estimate the dominant source using |Q|/r², then compute components. Compare prediction, arithmetic and a field-line sketch. If they disagree, identify whether the first error was direction, distance, symmetry or sign. Redo the same geometry with every source sign reversed; the field should reverse while its magnitude stays unchanged.

Also practise dimensional analysis: kQ/r² gives N/C, while qE gives N. If a result labelled electric field still contains the chosen test charge, revisit the source–probe separation. Write one unit line under every formula and estimate the dominant field before calculator work. These habits expose misplaced prefixes, squared distances and accidental magnitude addition before they reach the final answer.

Keep the corrected diagrams so recurring direction errors can be distinguished from isolated arithmetic slips during spaced review.

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