JEE MAIN - Physics (2022 - 25th June Evening Shift - No. 11)
A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of magnetic field will be equal to
B
2B
4B
$${B \over 2}$$
Explanation
$$B = {\mu _0}ni$$
Now $$i \to 2i$$
And $$n \to {n \over 2}$$
$$B' = {\mu _0}{n \over 2} \times 2i = {\mu _0}ni = B$$
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