Why wouldn't you use a steel core as an electromagnet?

this is because Steel is more difficult to magnetise and demagnetise but an iron core makes a temporary electromagnet because its lose its magnetism when the switch is open and and steel core is used to make a permanent electromagnet

what's the rest of the question

relative humidity, temperature and dew point -- are bound together in the mathematical relationship below. relative humidity changes when temperatures change. because warm air can hold more water vapor than cool air, relative humidity falls when the temperature rises if no moisture is added to the air. so i would say a