A tightly wound solenoid is 15 cm long, has 350 turns, and carries a current of 3.0 A. If you ignore end effects, you will find that the value of the vector B at the center of the solenoid when there is an iron core of magnetization M = 1.4 × 10^6 A/m is approximately a) 8.8 mT
b) 1.8 mT
c) 7.0 mT
d) 6.2 mT

A47.2 g block of copper whose temperature is 480 k is placed in an insulating box with a 91.8 g block of lead whose temperature is 200 k. (a) what is the equilibrium temperature of the two-block system? (b) what is the change in the internal energy of the two-block system between the initial state and the equilibrium state? (c) what is the change in the entropy of the two-block system? the heat capacities of copper and lead are 386 j/kg·k and 128 j/kg·k, respectively.