A straight wire of diameter 0.5 mm carrying a current of 1A is replaced by another wire of 1mm diameter carrying the same current. The strength of magnetic field far away is

# A straight wire of diameter 0.5 mm carrying a current of 1A is replaced by another wire of 1mm diameter carrying the same current. The strength of magnetic field far away is

1. A

twice the earlier value

2. B

half the earlier value

3. C

quarter of its earlier value

4. D

unchanged

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### Solution:

we know $B=\frac{{\mu }_{0}i}{2\mathrm{\pi r}}$, B is independent of diameter. So the strength of magnetic field remain unchanged

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