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Current Electricity — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsCurrent Electricity1 Mark
Question
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, and R is also false.
Assertion: The current flowing through a conductor is directly proportional to the drift velocity.
Reason: As the drift velocity increases the current following through the conductor decreases.
✓

Answer

  1. A is true, but R is false.

Explanation:

Consider a conductor of length l and area of cross section A. Time taken by the free electrons to cross the conductor, $\text{t}=\frac{\text{l}}{\text{v}_\text{d}}$

Hence, current, I = Anevd

Or $\text{I}\propto\text{v}_\text{d}$

Thus current is directly proportional to drift velocity.

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