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Define relaxation time of the free electrons drifting in a conductor: How is it related to the drift velocity of free electrons? Use this relation to deduce the expression for the electrical resistivity of the material.
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Relaxation time is the time interval between two successive collisions of electrons in a conductor, when current flows. I=current n = no. of free electrons a=area of conductorv=drift velocity e=charge of electron v=(eEm)T E= field m=mass of electron T= Relaxation timeFrom this, you can find expression of relaxation time
T=vmeEField is VL L=Length and V=IR.From this you can modify the expression in terms of resistivity.
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Q4
(i) Define the term drift velocity.
(ii) On the basis of electron drift derive an expression for resistivity of a conductor in terms of number density of free electrons and relaxation time. On what factors does resistivity of a conductor depend?
(iii) Why alloys like constantan and maganin are used for making standard resistors?
OR
(i) State the principle of working of a potentiometer.
(ii) In the following potentiometer circuit AB is a uniform wire of length 1m and resistance 10 Ω. Calculate the potential gradient along the wire and balance length AO(=1).
(ii) On the basis of electron drift derive an expression for resistivity of a conductor in terms of number density of free electrons and relaxation time. On what factors does resistivity of a conductor depend?
(iii) Why alloys like constantan and maganin are used for making standard resistors?
OR
(i) State the principle of working of a potentiometer.
(ii) In the following potentiometer circuit AB is a uniform wire of length 1m and resistance 10 Ω. Calculate the potential gradient along the wire and balance length AO(=1).
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