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Grade: 12
        
 the relaxation time t is nearly independent of applied E whereas it changes significantly with temprature  T. first fact is responsible for ohm’s law whereas second fact leads to variation of p with temprature. elaborat e why?
 
9 months ago

Answers : (3)

Arun
15066 Points
							
Dear student

Relaxation time is bound to depend on velocities of electrons and ions.

Applied electric field affects the velocities of electrons by speeds at the order of 1 mm/s, an insignificant effect.

Change in T, on the other hand, affects velocities at the order of 102 m/s. This can affect τ significantly.

[ρ = ρ (E, T) in which E dependence is ignorable for ordinary applied voltages.]

Regards

Arun (askIITians forum expert)

9 months ago
Ashutosh
12 Points
							Here T,m are relaxation time and mass of electronAs we know.....i=neAv v is drift velocityv=((-eE)/m)*TSince,E=-V/lOn putting these valuesi=(ne^2ATV)/(ml)As P=RA/lHere,P is resistivitySince,R=ml/(ne^2AlT)Therefore, P=m/(ne^2T)Thus,change in temperature implies change in T which implies change in resistivity (P)
						
8 months ago
Ashutosh
12 Points
							Here T,m are relaxation time and mass of electron As we know..... i=neAv v is drift velocity v=((-eE)/m)*T.  Since,E=-V/l. On putting these values. i=(ne^2ATV)/(ml). As P=RA/l. Here,P is resistivity Since,R=ml/(ne^2AlT) Therefore, P=m/(ne^2T) Thus,change in temperature implies change in T which implies change in  resistivity (P)
						
8 months ago
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