Showing posts with label Class Notes: Physics II. Show all posts
Showing posts with label Class Notes: Physics II. Show all posts

## Value of Half-Life Period

From the law of radioactive disintegration, we know,

## The Law of Radioactivity Disintegration:

Let, N be the number of atoms present in the radio element at a given instant t. Then the rate of decrease,

Here, λ is the disintegration constant. It is defined as the ratio of the amount of the substance which disintegrates in a unit time to the amount of substance present.

## General Properties of Nucleus:

### (i) Nuclear Size:

From Rutherford’s work, the mean radius of nucleus is  and the radius of the atom is . Thus the radius of the nucleus is 10,000 times smaller than the radius of the atom.

The empirical formula for the nuclear radius is,

Here, A is the mass number,  is a constant.

From this formula the radius of the Carbon () nucleus is.

## The Required de Broglie Wavelength:

A photon of light of frequency  has the momentum,

But, . Therefore, the momentum of the photon can be expressed in terms of wavelength λ as,

The wavelength of a photon is, therefore, specified by its momentum according to the relation,

## Einstein’s Photoelectric Equation :

According to Einstein, light of frequency  consists of a shower of photons, is of energy . When a photon of light of frequency  is incident on a metal, a part of the energy acquired by the electron is used to pull out the electron from the surface of the metal and the rest of it is utilized in imparting K.E. to the emitted electron.

## Electric Flux

For an arbitrary closed surface, the net outward flow or flux is the product of the average outdrawn normal component of the vector and the area of surface. Electric flux is used to express the relation between  and its source. Flux is denoted by

= (average normal component)×(surface area)

The unit of electric flux is newton-meter2/coul.

## Flux

If  is a vector field, then the flux through any face is defined as the scalar product of the vector area of the face and the vector . That is,

Flux = (component of velocity normal to the face) × (area of the face)

The amount of flux per unit area is defined as the divergence of the vector

## Electric Charge

The reason present in a material causes static electricity, electric field in the material and the material become able to attract other materials is called electric charge. It may be positive or negative. Unit of electric charge is coulomb (C).