SCIENCE · INVESTIGATE AND EXPLAIN

Keep electric and magnetic forces signed at entry

Electric and magnetic forces must be added as vectors before a cancellation is claimed. The supplied entry velocity is along +x, electric field .6 N/C along +y and magnetic field .2 T along +z. A right-handed coordinate system gives v cross B along −y. Therefore the net entry force is q(.6−.2v) in the y direction, with charge in coulombs.

Learning outcome: Compare speeds2,3,4 m/s for both charge signs and neutral charge. Retain component forces before summing. Explain why a neutral undeflected record and a nonzero-charge balanced record support different inferences.

Starting recap

Use a right-handed coordinate system, oriented surface normal, signed charge/current and declared energy boundary. Separate an entry force from a trajectory, emf from current, and rms from signed average.

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Try

At v=2 m/s and q=+1 µC, electric force is +.6 µN and magnetic force −.4 µN, leaving +.2 µN. At q=−1 µC both reverse and net force is −.2 µN. At v=3 m/s either nonzero sign balances.

Open the experiment

Predict

A neutral particle with zero entry deflection establishes:

Your prediction and reason

Experiment

Compare speeds2,3,4 m/s for both charge signs and neutral charge. Retain component forces before summing. Explain why a neutral undeflected record and a nonzero-charge balanced record support different inferences.

Keep electric and magnetic forces signed at entry

Worked teaching model · synthetic values · Uniform E=.6 N/C along +y and B=.2 T along +z at entry. Velocity has only +x component. Calculate entry forces, not finite-aperture transmission or a complete later trajectory. Fictional passive particle, virtual only.

Entry velocity along +x: 3 m/s Passive particle charge: 1 µC

Reset keeps your prediction, captures and practice history.

Signed entry force versus speed

Unlike graph quantities rescale independently; read units and values, not screen angles. 1: same fields and charge (solid). Joined curves show the supplied model, not additional observations.

Equivalent numerical coordinates for Signed entry force versus speed

same fields and charge

entry speed (m/s)	net y force (N)
1	4e-7
1.1	3.8e-7
1.2	3.6e-7
1.3	3.4e-7
1.4	3.2e-7
1.5	3e-7
1.6	2.8e-7
1.7	2.6e-7
1.8	2.4e-7
1.9	2.2e-7
2	2e-7
2.1	1.8e-7
2.2	1.6e-7
2.3	1.4e-7
2.4	1.2e-7
2.5	1e-7
2.6	8e-8
2.7	6e-8
2.8	4e-8
2.9	2e-8
3	0
3.1	-2e-8
3.2	-4e-8
3.3	-6e-8
3.4	-8e-8
3.5	-1e-7
3.6	-1.2e-7
3.7	-1.4e-7
3.8	-1.6e-7
3.9	-1.8e-7
4	-2e-7
4.1	-2.2e-7
4.2	-2.4e-7
4.3	-2.6e-7
4.4	-2.8e-7
4.5	-3e-7
4.6	-3.2e-7
4.7	-3.4e-7
4.8	-3.6e-7
4.9	-3.8e-7
5	-4e-7

At most 82 representative computed coordinates including endpoints; the plotted curve can use a finer grid. A table of a revealed generator is not independent measurement evidence.

Calculated quantities under the declared measurement model
Quantity	Value	Unit
Electric force y	6e-7	N
Magnetic force y	-6e-7	N
Net entry force y	0	N
Nonzero-charge balanced entry speed	3	m/s
Entry magnetic power	0	W
Entry electric power	0	W

Charge sign reverses both entry forces; the nonzero-charge balance speed depends on the field ratio.

For velocity +x and field +z, v cross B points −y. Add qE and q(v cross B) as vectors. At balanced entry v=E/B=3 m/s, nonzero charges have zero net entry force. A neutral particle has zero force at every speed and therefore does not test that ratio. Both forces are transverse at this instant, but a later deflected velocity can allow electric work; this entry calculation does not certify finite-aperture transmission.

Predict before inspecting the values. Save contrasting records with assumptions and one alternative explanation. This virtual display does not certify practical measurement technique.

Charge sign reverses both entry forces; the nonzero-charge balance speed depends on the field ratio.

Observation to attach to a capture

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

Understand

Define vectors, source and system boundary

Derive the quantitative comparison

For a nonzero charge, the balance speed is E/B=3 m/s. Changing the sign of charge reverses both force contributions, leaving that nonzero-charge balance speed unchanged. A neutral particle has zero electric and magnetic force at every speed in this passive model, so its undeflected entry cannot measure E/B. Field magnitudes alone do not determine the result without the declared directions.

Separate physical evidence from a model extension

At the entry instant both forces are perpendicular to velocity, so both instantaneous powers F dot v are zero. Magnetic force remains perpendicular to the instantaneous velocity and never does work. Electric force can do work later if the particle develops a component of velocity along E. An entry balance does not by itself establish transmission through a finite apparatus: field extent, fringe effects, initial position and aperture geometry would also be needed. This is a virtual local-force comparison, not a particle-selector construction task.

Worked original case

At v=2 m/s and q=+1 µC, electric force is +.6 µN and magnetic force −.4 µN, leaving +.2 µN. At q=−1 µC both reverse and net force is −.2 µN. At v=3 m/s either nonzero sign balances.

Investigation

Changed-case practice

Try the changed case before feedback

Keep the stated fields but use v=4 m/s and q=−2 µC. Find net y force in µN.

Numerical result in the requested units

This practice is public and unsaved. A matching number does not verify understanding. Retain your explanation, assumptions and changed-case evidence in the separate course workspace.

Sources and evidence boundary

Original prose and numerical cases checked 30 October 2026 against the relevant primary explanation. All records and diagrams are virtual. No real coil, powered wire, high-field exposure, motor, transformer, mains connection or inductor switching is requested. Retain first predictions, contrasting recipes and independent criterion review; public agreement is not practical certification or demonstrated mastery.

Apply

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

Which independent observation could reject this model rather than merely refit its parameters?

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

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