Question: Q. 5. The following table gives the length of three copper wires, their diameters, and the applied potential difference across their ends. Arrange the wires in increasing order according to the following :

(i) The magnitude of the electric field within them,

(ii) The drift speed of electrons through them, and

(iii) The current density within them.

R] [CBSE SQP 2017-18]

Wire No. Length Diameter Potential
Difference
1 $L$ $3 d$ $V$
2 $2 L$ $d$ $V$
3 $3 L$ $2 d$ $2 V$
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Solution:

Ans. (i)

$$ \begin{aligned} & E_{1}=\frac{V}{L}, E_{2}=\frac{V}{2 L}, E_{3}=\frac{2 V}{3 L} 1 / 2 \ & E_{2}<E_{3}<E_{1} \end{aligned} $$

(ii)

$$ v_{d} \propto E $$

$$ v_{d 2}<v_{d 3}<v_{d 1} $$

$$ \begin{align*} & I=n e A v_{d} \tag{iii}\ & J=n e v_{d} \end{align*} $$

$$ J_{2}<J_{3}<J_{1} $$

[CBSE Marking Scheme 2017]



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