In some Northern European nations, homes are being built without heating systems of any type. They are very well insulated and are kept warm by the body heat of the residents. However, when the residents are not at home, it is still warm in these houses. What is a possible explanation?

PHYS 242 BLOCK 2 NOTES Sections 23.1 to 23.5 → Rewriting GeneralPhysics I’s Eq. (6.14) as Eq. (23.1), the wora→b done by a force F in moving a b ⌠ b particle from pointa to pointb is defined toa→bW≡ F·dl = ⌡F cos φ dl . a a If the force is conservatia→bW= U a U ,bwhereU is the potential energy associated with that force. b ⌠ If we have a test chargeq outside a spherically-symmetric, same-sign chargeq,= F·dl = 0 a→b a b 1 qq0 ⌡F cos φ dl , whereF =4πε0 r2 and dl cos φ = dr (see Fig. 23.6).Then integrating aromb to r gives us a 1 qq 0 1 qq 0 1 qq 0 4πε0 ra – 4πε0r b = Ua– U b Thus the simplest choice for the potential energy expression 4πε 0 r . This equation also holds for opposite-sign charges. Any equation in this block cε0