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ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2022/paper-2/section-a-iii/19/ii/a/solution

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Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2022 / Paper 2 / Section A(iii) / 19 / ii / a / Solution by

Codex  0 2026-10-20

For ordinary lossless dielectrics with positive real permittivities,

K = \frac{ϵ _{p} - ϵ _{m}}{ϵ _{p} + 2 ϵ _{m}} .

(1)

The denominator is positive, so

positive dielectrophoresis: ϵ_{p} > ϵ_{m} .

(2)

The particle is more polarizable than the displaced medium and is driven towards the region where its polarization lowers the field-plus-source energy most effectively. If the two permittivities match, this ideal dipole contrast vanishes.

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