Question

Explanation of Principal quantum Number!!
And Explain Photo electric Effect!!

Answer 1

Helloo!!

1. principal Quantum Number!!

This is the most important quantum number as it determines the size and to large extent the energy of the orbital for hydrogen and hydrogen like species energy and size of the orbital depend only on n the average energy of the electron is directly proportional to the principal quantum number that is E is directly proportional to n as a energy is required in moving away the negatively charged electron from the positively charged nucleus the energy of the orbital will increase in and the size of the orbital increase with an increase in the principal quantum number in other words for higher value of n the electron will be located away from the nucleus the principal quantum can assume any positive integral value of n it also identify the energy level or energy cell designated as K, L, M, N... corresponding to the number of and the maximum number of electron in a shelll is given by 2n²

PHOTOELECTRIC EFFECT!!

The phenomenon of ejection of electrons from the surface of a metal when light of Suitable frequency strike on it is called photoelectric effect. 
The emitted electrons are called photoelectrons.
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Explanation for photoelectric effect 

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Einstein by using planks quantum theory of electromagnetic radiation gave the explanation for photoelectric effect. 

when a photon having sufficient energy strikes on electrons on the metal atom. it transfers ita energy instantaneously to the electron during the collision and electrons gets ejected without any delay.

Greater the energy possessed by the photons, greater will be the transfer of energy to the electron and greater will be the K.E possessed by the photoelectrons. 

The energy which is supplied by the photon to the to the electron is used to set up to eject the electron from the metal atom and the remaining is used to eject electron with maximum K.E.

Energy of striking photon = threshold energy + K.E of the ejected electron 

Energy of striking photon = hv from planks quantum theory..
Binding energy = threshold energy (hv°) 

therefore, hv = hv° + 1/2 MeV^2

application for photoelectric effect 
1. used to produce sound in cinematography 
2. uesd in blugar alarms
3. used in automatic opening and closing of doors

hope this helps you....

Answer 2

Principal Quantum Number -

1) Given by Bohr.
2) Denoted by letter 'n'.
3) It determines the energy level or energy shell in which an electron occurs in an atom.
4) It also determines the energy associated with the energy level.
5) It determines the approximate distance between the electron of a particular shell and the nucleus.
6) Principal quantum number determines the energy of Hydrogen electron and other species like He+, Li2+ which have only 1 electron.
7) For a species containing more than 1 electron , it can only determine the probable energy associated with the electron


Photo electric effect --

This effect is defined as the ejection of electrons from the surface of metal after it is stricken with photons.

This effect can only be explained of we assume the particle nature of light.

Light has small particles called photons. Photon is a source of energy and the expression is given by E = hv.
h = Planck's constant
v (nu) = Frequency of light.

Now, every electron is held by the nucleus of the atom in which it occurs by some force which is called The binding force. For the electrons to escape this binding force some external energy has to be provided in order to overcome this binding force.

This escape energy is given by photons .It is given by E = hv° also known as threshold energy . Here v° is threshold frequency.

Sometimes the energy provided by the photons maybe greater than the minimum threshold energy needed. So the excess is given out as kinetic energy of electrons that are ejected out .

So, we get an expression as -->
hv = hv° + 1/2mv^2

Keeping some points in mind.

1) If the energy provided by photons is less than the threshold energy required then no electrons will be ejected.

2) If the energy is equal to the threshold energy required then electrons will be just emitted from the surface.

3) If the photons energy is more than threshold energy then the electrons ejected will have some kind of kinetic energy.

Hope This Helps You!