You decide to build your own RC circuit out of scrap. To build the capacitor you use two square sheets of aluminum foil 10cm on a side) with cellophane sandwiched between them (e.g., Saran Wrap). Your cellophane has a dielectric constant K=3.5 and a thickness 0.0125mm. You also connect the plates together with 25m of 30 gauge (0.255mm diameter) copper wire (of resistivity rho=1.72×10^−8Ωm). Required:

Find the RC~time constant τ that describes how a charge on the capacitor would decay with time. (You may ignore resistance within the aluminum foil. The vacuum permittivity of free space is ϵ0=8.854×10−12C^2/Nm^2.)