點解水可以吸microwave & ultrasound??

1. Water molecules are in the form of dipoles, i.e. because the electrons are unevenly distributed so that one end of the molecule is positively charged and the other end negatively charged.

Microwave is electromangetic wave that propagates with changing electric and magnetic fields. When water molecules interact with microwave, the electric filed component of the wave casues the dipole to vibrate. Such vibration takes away (i.e. absorb) energy from the microwave to become the kinetic energy of vibration for the water molecules.

2. Generally, when waves, irrespective it is electromagnetic in nature (e.g. light, radio wave, or even X or gamma rays... etc) or mechanical in nature (e.g. sound wave) will be absorbed by water as water dipole molecules are forced to vibrate by the wave that passes through.

1. water molecules vibrate at a certain frequency.
any waves that have similar frequency will be absorbed
by water molecules. microwave and ultrasound have frequency
similar to water molecules. so the energy of the waves can be
absorbed by water molecules.
2. so any waves that have similar frequency to water molecules
can transfer energy to water molecules.

Because water molecules are special, with oppsite charges each end. This is why they can absorb energy from mircowave