Which combination of a wire coil and a core would make the weakest electromagnet?
O A. 20 coils of bare wire around a steel core
B. 20 coils of insulated wire around a hollow cardboard core
O C. 50 coils of insulated wire around a hollow cardboard core
D. 50 coils of bare wire around a steel bolt

An insulated thermos contains 148 g of water at 72.7 ˚c. you put in a 11.7 g ice cube at 0.00 ˚c to form a system of ice + original water. the specific heat of liquid water is 4190 j/kg•k; and the heat of fusion of water is 333 kj/kg. what is the net entropy change of the system from then until the system reaches the final (equilibrium) temperature?