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Electric Charges and Fields — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsElectric Charges and Fields1 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 (A): If a point charge be rotated in a circle around a charge, the work done will be zero.
Reason (R): Work done is equal to dot product of force and distance.
✓

Answer

  1. Both A and R are true, and R is the correct explanation of A.

Explanation:

Work done will be zero because in rotating the charge in a circle, force is along the radius, and direction of motion is perpendicular to it.

$\therefore$ Work done, $\text{W}=\vec{\text{F}}\cdot\vec{\text{S}}=\text{FS}\cos\theta=\text{FS}\cos90^\circ=0$

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