Question: Q. 11. Write the expression for the drift velocity of charge carriers in a conductor of length $l$ across which a potential difference $V$ is applied.
R [O.D. Comptt. I, II, III 2014]
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Solution:
Ans. $\quad v_{d}=\frac{-e V}{m l} \tau$
[CBSE Marking Scheme 2014]
Detailed Answer :
Since drift velocity, $v_{d}=\frac{-e E}{m} \tau$
But,
Now, from equation (i)and (ii),
Drift velocity, $\quad \nabla_{d}=\frac{-e V}{m l} \tau$
[AT Q. 12. How does one explain increase in resistivity of a metal with increase in temperature?
U [O.D. Comptt. I, II, III 2014]
Ans. With increase in temperature, the relaxation time (average time between successive collisions) decreases and hence resistivity increases.
Alternatively,
Resistivity, $\rho=\left(\frac{m}{n e^{2} \tau}\right)$ increases as $\tau$ decreases with increase in temperature.
[CBSE Marking Scheme 2014]
