A charge q is enclosed by an imaginary Gaussian surface.

If radius of surface is increasing at the rate $\frac{\mathrm{dr}}{\mathrm{dt}}$ = K, then

flux linked with surface is increasing at the rate $\frac{\mathrm{d\varphi }}{\mathrm{dt}}=\mathrm{K}$

flux linked with surface is decreasing at the rate $\frac{\mathrm{d\varphi }}{\mathrm{dt}}=-\mathrm{K}$

flux linked with surface is decreasing at the rate $\frac{\mathrm{d\varphi }}{\mathrm{dt}}=\frac{1}{\mathrm{K}}$

flux linked with surface is $\frac{\mathrm{q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$