Compared to permanent magnets, why are electromagnets more useful in many modern technologies?
O A. In permanent magnets, the strength of the magnetic field is more
consistent.
O B. To use an electromagnet, a power supply is not necessary.
O C. Strong permanent magnets are too large to use.
O D. By controlling the current, electromagnets can be turned on and
off.

The lid of a pressure cooker forms a nearly airtight seal. steam builds up pressure and increases temperature within the pressure cooker so that food cooks faster than it does in an ordinary pot. the system is defined as the pressure cooker and the water and steam within it. if 2.0 g of water is sealed in a pressure cooker and then vaporized by heating, and 5127 j must be added as heat to completely vaporize the water, what is the change in the system’s internal energy? answer in units of j.