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GUJCET · Physics · Current Electricity
As following figure 2 A current passing through a conducting wire, radius of cross-sectional of wire at point A is 3r and point B is r respectively. Then find the ratio of drift velocity at point A and B.
- A 3
- B \(\frac{1}{9}\)
- C \(\frac{1}{3}\)
- D 9
Answer & Solution
Correct Answer
(B) \(\frac{1}{9}\)
Step-by-step Solution
Detailed explanation
(B)
from I \(=n A v_d e\)
\(v_d=\frac{ I }{n A e}\)
\(\begin{array}{l}\therefore \quad v_d \propto \frac{1}{A} \propto \frac{1}{r^2} \\ \therefore \quad \frac{\left(v_d\right)_{ A }}{\left(v_d\right)_{ B }}=\frac{(r)^2}{(3 r)^2}=\frac{1}{9}\end{array}\)
from I \(=n A v_d e\)
\(v_d=\frac{ I }{n A e}\)
\(\begin{array}{l}\therefore \quad v_d \propto \frac{1}{A} \propto \frac{1}{r^2} \\ \therefore \quad \frac{\left(v_d\right)_{ A }}{\left(v_d\right)_{ B }}=\frac{(r)^2}{(3 r)^2}=\frac{1}{9}\end{array}\)
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