Question

a) Water makes life possible. The cells of your body could not function without water in which to dissolve essential biological molecules. What electrical properties of water make it such a good solvent? b) When a credit card is “swiped” through a card reader, the information coded in a magnetic pattern on a back of the card is transmitted to the card holder’s bank. Why? Is it necessary to swipe the card rather than holding it motionless in card reader slot? Which of the Maxwell’s equation explains how a credit card reader works? c) Is it possible to have a purely electric wave propagate through empty space which is a wave made up of an electric field but no magnetic field? What about purely magnetic wave, with a magnetic field but no electric field? Please explain your answer by using Maxwell’s equation concept

Answer 1

(a) Water molecules have a permanent electric dipole moment: One end of the molecule has a positive charge and the other end has a negative charge. These ends attract negative and positive ions, respectively, holding the ions apart in solution. Water is less effective as a solvent for materials whose molecules do not ionize (called nonionic substances), such as oils.

(b) A magnetic stripe card is a type of card capable of storing data by modifying the magnetism of small iron-based magnetic particles on a band of magnetic material on the card. The magnetic stripe, sometimes called swipe card or magstripe, is read by swiping past a magnetic reading head.

Yes, it is necessary to swipe the card because then only the magnetic flux will change and emf is induced.

3rd Maxwell's equation explains the working of credit card reader which is based on Faraday's law of electromagnetic induction.

(c) No, it isn't possible to create magnetic waves without an electric field being present.

While electric charges can create E-fields, magnetic fields can also create E-fields. Similarly, E-fields can also create magnetic fields. In fact, every time you change a magnetic field, you create an electric field. This is called Faraday's Law of Induction.

​​​​​​Similarly, every time you change an electric field, you create a magnetic field. This is called the Maxwell-Ampere Law.

The interesting thing is that a changing electric field creates a changing magnetic field, which creates a changing electric field, which creates a changing magnetic field, and so on.