a sunlight consists of seven colours (violet,indigo,blue,green,yellow,orange,red) VIBGYOR.The wavelength of the violet colour is lowest amongst this seven colour and the wavelength of the red colour is highest.Our atmosphere consists of many particles ,gases etc.We know when a particular light collides with a particle it gets scattered and the phenomnon is called scattering.This scattering is related to wavelength by the given relation.......
degree of scattering is inversely proportinal to the 4th root of wavelength.So when a sunlight comes to our earth , the violet colour of it having the lowest wavelength gets highly scattered while the red colour gets scattered to a small degree.So when a person see towards sky neither the violet nor the red colour reaches his eye only blue colour which has got medium wavelength gets scattered to some degree such that it reaches the earth and so it appears blue to us. Thus sky appears blue to us.
Thursday, February 14, 2008
Monday, February 4, 2008
Photo electric effect
whenever a light of high frequency strikes a metal surface then outer electron of that metal gets ejected .This phenomenon is known as photoelectric effect and the electrons emitted is known as photoelectrons.
Let us a take a evacuated tube consisting of a two electrode anode and cathode connected to a variable voltage . when a light falls of sufficient frequecy falls on cathode electrons are emitted and it is attracted towards poitive terminal i.e anode .If both the electrodes are externally connected current flows through it and it is called photo electric current.
This photoelectric current depends on following condition.
1)if we increase the intensity of incident light i.e increase the number of photons per unit area more electron get emitted due to more collision of photons withelectron of that anode.2)If we make the anode more positive more emitted electron from cathode gets attracted towards anode, so more is the current.3)if we increase the frequency of the incident light (i.e energy) more is the energy of the emitted electron and it moves easily towards the anode due to its K.E and more is the current.
Now if we make the anode negative then ejected eletron gets repelled but the emitted electron with sufficent energy overcome this rpulsion and make its way towards anode and reach there.IF we make the anode more negative then for some particular negative voltage on this anode no electron can reach it due to repulsion.This negative voltage is known as stopping potenial
Let us a take a evacuated tube consisting of a two electrode anode and cathode connected to a variable voltage . when a light falls of sufficient frequecy falls on cathode electrons are emitted and it is attracted towards poitive terminal i.e anode .If both the electrodes are externally connected current flows through it and it is called photo electric current.
This photoelectric current depends on following condition.
1)if we increase the intensity of incident light i.e increase the number of photons per unit area more electron get emitted due to more collision of photons withelectron of that anode.2)If we make the anode more positive more emitted electron from cathode gets attracted towards anode, so more is the current.3)if we increase the frequency of the incident light (i.e energy) more is the energy of the emitted electron and it moves easily towards the anode due to its K.E and more is the current.
Now if we make the anode negative then ejected eletron gets repelled but the emitted electron with sufficent energy overcome this rpulsion and make its way towards anode and reach there.IF we make the anode more negative then for some particular negative voltage on this anode no electron can reach it due to repulsion.This negative voltage is known as stopping potenial
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