Question

1) Describe what polarization means in the context of electric charges. Generally, under what circumstances would I see polarization happen? (describe how the charges are distributed pre- and post- polarization). Water is said to be a polar molecule; what does that mean in this context?

2) Plasma is a state of matter that has been completely ionized; meaning that there are no electrons bound to protons, and both the electrons and protons are able to move about freely. If I have a positively charged surface and bring it near to a plasma, what would happen? Will both the electrons and protons behave in the same way? (compare their accelerations).

Answer 1

1. Polarization means slight separation between the centre of mass of positive charge (protons) from the centre of mass of negative charges (electrons) within the atoms of an insulating or dielectric material.

Polarization occurs when the dielectric is placed in an external electric field.

The electric field exerts forces on the charges of the atoms of the dielectric material, causing the negative charges to move slightly from positive charges in a direction opposite to the direction of the electric field. Thus, each atom of the dielectric now become an induced dipoles having a net dipole moment along the direction of the external electric field.

Water is said to be a polar molecule, because in case of a water molecule, the centre of mass of positive charges (two hydrogen atoms) does not coincide with the centre of mass of the negative charge (oxygen atom). This makes the water molecule to posses an inherent dipole moment.