What is an advantage of using an electromagnet rather than a regular magnet

Acertain radio station broadcasts radio waves that have a wavelength of 298cm what is its broadcast frequency?

Refrigerant-134a flows through a carnot heat pump cycle at 0.5 kg/s. it is known that the maximum absolute temperature in the cycle is 1.1 times the minimum absolute temperature, and the net power input to the cycle is 2.5 kw. if the refrigerant changes from a saturated vapor to a saturated liquid during the heat rejection process, determine the maximum magnitude of the enthalpy of vaporization for this process in kj/kg (with 3 significant figures).

Which is a substance that can be separated by physical means and is not the same throughout