JEE MAIN - Physics (2024 - 5th April Evening Shift - No. 30)
Explanation
The magnetic field inside a solenoid can be calculated using the formula:
$$B = \mu_0 n I$$
where:
- $B$ is the magnetic field in teslas (T),
- $\mu_0$ is the permeability of free space ($4\pi \times 10^{-7} \mathrm{~Tm/A}$),
- $n$ is the number of turns per unit length of the solenoid (turns/m),
- $I$ is the current in amperes (A).
Given:
- The magnetic field $B = 6.28 \times 10^{-3} \mathrm{~T}$,
- The current $I = 5 \mathrm{~A}$,
- The length of the solenoid $L = 0.5 \mathrm{~m}$,
First, let's calculate the number of turns per unit length $n$, which is $n = \frac{m}{L}$ where $m$ is the total number of turns and $L$ is the length of the solenoid.
Rearrange the formula for $B$ to solve for $m$:
$$B = \mu_0 \frac{m}{L} I$$
Therefore,
$$m = \frac{B L}{\mu_0 I}$$
Substituting the values we have:
$$m = \frac{(6.28 \times 10^{-3} \mathrm{T}) (0.5 \mathrm{m})}{(4\pi \times 10^{-7} \mathrm{Tm/A}) (5 \mathrm{A})}$$
$$m = \frac{6.28 \times 10^{-3} \times 0.5}{4\pi \times 10^{-7} \times 5}$$
$$m = \frac{6.28 \times 0.5 \times 10^{-3}}{20\pi \times 10^{-7}}$$
$$m = \frac{3.14 \times 10^{-3}}{20 \pi \times 10^{-7}}$$
$$m = \frac{3.14 \times 10^{-3}}{20 \times 3.14 \times 10^{-7}}$$
$$m = \frac{1}{20 \times 10^{-4}}$$
$$m = \frac{1 \times 10^4}{20}$$
$$m = 500$$
Therefore, the value of $m$ is 500 turns.
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