How sugar or oil gets heated in microwave although there is no moisture???

Dipole rotation is the mechanism normally referred to as dielectric heating, and is most widely observable in the microwave oven where it operates most efficiently on liquid water, and much less so on fats and sugars. This is because fats and sugar molecules are far less polar than water molecules, and thus less affected by the forces generated by the alternating electromagnetic fields. 

Outside of cooking, the effect can be used generally to heat solids, liquids, or gases, provided they contain some electric dipoles. While a much poorer microwave absorber than water, oils still do absorb microwave energy and heat, especially if the quantity of oil is large. Also, oils have a specific heat capacity of about 0.5, which is half that of water (1.0) and that means that for a given amount of microwave energy absorbed oil will heat twice as much as water. 

But be extraordinarily careful while heating oil inside a microwave oven because oils can easily reach temperatures of over 400 F. This can cause serious burns. So, it is best not to heat them inside a microwave oven. Heating in microwave is mainly for polar substances. So oil and sugar are polar but less than water. Hence their heating is possible taking precaution of their smoke pt. and flash pt. This is why sugar usually catches fire in microwave.




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