Answer the following:
$(i)$ How electromagnetic waves are produced by an oscillating charge?
$(ii)$ State clearly how a microwave oven works to heat up a food item containing water molecules.
$(iii)$ Why microwaves are found useful for the radar system in aircraft navigation?

Hint: An electromagnetic wave is a propagating wave which travels in space with the speed of light and having both electric and magnetic field components. Microwave is a form of electromagnetic radiation whose wavelength lies in the region of $1m - 1mm$.Radar is a detection system which is used to find velocity or range of particular bodies.

Complete answer:
$(i)$ As we know, a charge produces an electric field around it and when this charge oscillates it also produces an magnetic field but when this charge starts to move in space it continuously produces oscillating electric and magnetic fields hence propagation of electromagnetic waves takes place. These electromagnetic waves travel with the speed of light in free space.

$(ii)$ Microwaves are designed in such a way that their frequency must be equals to the frequency of water molecules which is present in the food and this makes a resonance condition and hence the energy from waves get transferred to the water molecules results in increase in temperature of the food and hence food get heated.

$(iii)$ Since, In aircraft navigations waves need to travel much longer so we need a such type of waves which can travel much longer without losing their much energy so, microwaves as thy having short wavelength which means they have very low energy dissipation along the journey so, they are best to use in radar system communications.

Note:Microwaves have wavelength in the order of $1m - 1mm$ and their high frequency lies in the range of $300MHz - 300GHz$ . Due to their high frequency and low wavelength they are much widely used in other sectors like wireless networks or communication links cancer treatment and radio astronomy.