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Electrophoretic mobility is the drift velocity of a charged particle per unit electric field strength.
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Formula
μep in m2/(V·s) · v in m/s · E in V/m
| Symbol | Meaning | Unit |
|---|---|---|
| Signed electrophoretic mobility for a stated direction convention | m2/(V·s) | |
| Particle drift velocity | m/s | |
| Electric field strength | V/m |
\mu_{ep}=\frac{v}{E}Mobility is the signed particle velocity divided by the applied field strength. Its sign depends on charge and the chosen axis; in porous gels, measured apparent mobility can also reflect friction and sieving. Temperature, viscosity, buffer and ionic strength influence the value. This is a transport quantity, not a cell voltage or an electrode-potential difference.
Particles move with a defined drift velocity and measured field strength in the considered range.
Mobility is signed drift velocity per electric field strength.
Drift velocity
The sign follows charge and axis direction.
Given v=2.0×10−4 m/s and E=100 V/m, find the mobility magnitude.
|μep|=2.0×10−4/100=2.0×10−6 m2/(V·s).
Interpreting the sign without charge and field direction.
First define the positive axis, then use signed velocity.
Formula cluster
magnitude and direction depend on charge, medium and applied field.
An ion drifts at v=2.0×10−4 m/s in a field E=100 V/m. Then μep=v/E=2.0×10−6 m2/(V·s). Check: (m/s)/(V/m)=m2/(V·s). A negative ion has a negative sign for a fixed field direction, even if only the magnitude was calculated here.
Describe charge-dependent separation and migration times in capillary and gel electrophoresis
Here is how to work through a typical Electrophoretic Mobility (μep = v/E) task step by step:
Task
Given v=2.0×10−4 m/s and E=100 V/m, find the mobility magnitude.
Solution path
|μep|=2.0×10−4/100=2.0×10−6 m2/(V·s).
The relation describes how fast a charged particle drifts per unit field strength. Its output is mobility in m2/(V·s), including a sign convention.. magnitude and direction depend on charge, medium and applied field. It answers a bounded question and places Electrophoretic Mobility in a defined measurement or model context. It does not replace a complete process or system description. State the reference quantity and conditions before interpreting the number; only then can you tell whether it represents an amount, correction or efficiency.
The quantities are v is drift velocity and E is local electric-field strength. Their units are Dividing m/s by V/m gives m2/(V·s).. Use values on the same reference basis; a ratio across inconsistent phases, time intervals or standards would not be meaningful. Check the dimension of every term before calculating and keep conversions visible. This shows whether the result should be dimensionless or carry a unit. Dimensional analysis cannot repair a bad measurement, but it catches many calculation errors early.
The stated validity is: mobility can be influenced by viscosity, temperature and sieving. The calculation requires v and E are measured at the same location and under the same buffer conditions.. Outside this range, additional interactions, changed reference states or different geometries can alter the relation. If an assumption fails, do not transfer the result without qualification; name the limitation and use a more suitable model or measurement. This matters especially when comparing metrics collected under different experimental conditions. This assumption determines which samples and states the calculated value actually represents, so report it alongside the numerical result.
A representative case is: 2.0×10−4 m/s divided by 100 V/m gives 2.0×10−6 m2/(V·s). The check gives: Check dimensions and whether the sign matches charge direction.. Write substituted values with units, then put the result back into the original relation or balance. A successful check still depends on the model assumptions. Also test whether limiting cases behave plausibly, for example whether an ideal limit is recovered or a balance returns the overall composition. These checks are more informative than merely rounding to several decimal places. For an additional plausibility check, change one input at a time and confirm that the result moves in the expected direction.
A nearby concept is the cell potential of a galvanic cell.. The key difference is that Mobility describes particle motion per field; cell potential is a voltage between electrodes. Both relations may appear in related problems, but they answer different questions and do not automatically use the same data. Choose the equation by the requested output: magnitude and direction depend on charge, medium and applied field. If a problem asks for the cell potential of a galvanic cell. instead, use that definition. This distinction prevents similarly named metrics or models from being treated as interchangeable. This distinction also determines which measurements, reference states and intermediate steps must be documented for a reproducible analysis.
Quanta exam set
Curated exam set for "Electrophoretic Mobility":
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Which formula describes Electrophoretic Mobility?
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Question (front)
How do you rearrange Electrophoretic Mobility for Drift velocity?
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Which common mistake happens with Electrophoretic Mobility?
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Create a curated FSRS exam set for μep = v/E: formula recall, variables, derivation, rearrangement, worked example, common mistakes and exam context.
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