| Directions: In the following questions, a statement of Assertion [A] is followed by a statement of Reason (R). Mark the correct choice as: |
| Assertion [A]: When radius of circular loop carrying current is doubled, its magnetic moment becomes four times. |
| Reason (R): Magnetic moment depends on area of the Loop. |
A) Both Assertion [A] and Reason (R) are true and Reason (R) is the correct explanation of Assertion [A]
B) Both Assertion [A] and Reason (R) are true but Reason (R) is not the correct explanation of Assertion [A]
C) Assertion [A] is true but Reason (R) is false
D) Assertion [A] is false and Reason (R) is also false
Correct Answer: B
Solution :
(b) Magnetic dipole moment of the current loop \[\text{=Ampere turns }\!\!\times\!\!\text{ Area of the coil}\] Initially magnetic moment \[\overrightarrow{\text{M}}=l\,\pi {{r}^{2}}\], new magnetic moment \[\overrightarrow{\text{M}}=l\,\pi {{(2r)}^{2}}=4l(\pi {{r}^{2}})=4\overrightarrow{M}\] So magnetic moment becomes four times when radius is doubled.
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