The electric field inside a uniformly charged sphere with positive charge Q and radius R points radially outward from the center of the sphere and has magnitude E=Qr/4πϵ0R3 at a distance r from the center. By integrating the electric field, find the potential difference between the center of the sphere and its surface. Which is at higher potential: the center or the surface?

Consider a 1000 w iron whose base plate is made of 0.5 cm thick aluminum alloy 2024-t6 (ρ = 2770 kg/m3 and cp = 875 j/kg°c). the base plate has a surface area of 0.03 m2. initially, the iron is in thermal equilibrium with the ambient air at 22°c. assuming 90% of the heat generated in the resistance wires is transferred to the plate, determine the minimum time needed for the plate temperature to reach 200°c.