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# Tag Archives: dipole

## How does a microwave oven work?

Now, microwave oven is so popular that majority of houses have one. Many use it mainly to reheat food without loss of nutrient. The advantage is that the microwave heats up the food very fast.

Some observations made on microwave oven are,

• It does not heat up the vessels directly
• It is not able to cook food contained inside metal vessels
• If the turn table does not work, cooking will not be even.

So, it is pertinent to ask how the mechanism of heating in a microwave oven is different from other heating devices?

Here the water molecules, which are polar in nature play the magic. (A polar molecule is one in which the centre of mass of positive charges and the centre of mass of negative charges do not coincide and have a net dipole moment.) When microwaves are passed through food materials, the water molecules contained in them tends to turn and this rapid churning of water molecules develops a lot of heat. The turn-table adds to the churning and randomization developing heat more rapidly.

The food materials contained in a closed metal vessel will not be heated up by the microwave oven as they do not allow microwaves to pass through them. The metals are opaque to microwaves.

Why the food materials heated using microwave dry up and become stiff when cool?

In a microwave oven, the water molecules are heated very fats that the water is converted readily into steam. If kept open, the steam will escape and the material will become hard when cooled due to the decrease in the water content.

## Concept of magnetic dipoles

“Can u explain Concept of magnetic dipoles” – Sam Asked

Answer: A magnet always exist in pairs. A magnetic dipole consists of two equal and opposite poles separated by a small distance. The magnetic poles cannot exist alone. Monopoles does not exist.

A single current carrying loop is a simple practical  example for a magnetic dipole.

## Why does magnet attract only some of the materials like iron why not plastic ? What is the absolute reason behind it?

Why does magnet attract only some of the materials like iron why not plastic ? What is the absolute reason behind it? (Ankit Gururani posted in facebook)

The cause of magnetism is revolution of electrons. A revolving electron acts like a tiny magnet just like a current carrying coil does. If the magnetic moments of all the electrons nullify the effect of each other, it is non magnetic else it is a magnetic substance.

A magnetic substance consists of atoms or molecules having a net magnetic dipole moment. When an external magnetic field is applied or another magnet is brought near, the magnetic dipole moments get aligned and this results in the attraction of the magnetic substance by the magnet.

When the magnetic substance have their dipole moments aligned, it is said to be magnetised.

## How does dielectric constant depend on nature of medium?

How does dielectric constant depend on nature of medium?
Does this have any relation with free electrons and force between molecules?

Dielectric Constant, also called relative permitivity of a medium depends on the electric susceptibility of it, the ease with electric flux lines can pass through it.

The susceptibility depend on molecular polarization, the electric dipole moment acquired per unit volume in an external electric field.

So, the thing to note is that, dielectric constant is a physical quantity measured as a comparison of the strength of electric field in vacuum to that inside the material.

Dielectric constant can be defined in terms of electrostatic force

$K=\frac{F_{0}}{F_{m}}$

Dielectric Constant can also be defined in terms of capacitance.

$K=\frac{C_{m}}{C_{0}}$