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crc press - E-Lib FK UWKS

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196 Cell-Penetrating Peptides: Processes and Applications<br />

FIGURE 9.3 Schematic model for calculation of the electric intensity at P in the presence<br />

of a superficial density of charge δ.<br />

and at point P, a field dE, has a magnitude of<br />

The field can be solved into two components dE x and dE z. By symmetry, the<br />

components dE x will sum to zero for the entire sheet of charge. The resultant field<br />

at P is therefore in the z-direction, perpendicular to the sheet of charge. It is seen<br />

from the diagram that<br />

and hence<br />

dq<br />

dλ<br />

= = δdx<br />

L<br />

dE k dx<br />

q = 2 δ<br />

r<br />

dE z = dE sin θ<br />

E = dEz = 2kδ q<br />

+∞<br />

∫ ∫ −∞<br />

sin θ.<br />

dx<br />

r

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