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JEE Main 20257 AprilMorning Shift
Exam
JEE Main
Year
2025
Date
7 April
Shift
Morning Shift
Subject
Physics
Chapter
Magnetic Properties of Matter

JEE Main 2025 · 7 April · Morning Shift · Physics · Magnetic Properties of Matter

The percentage increase in magnetic field (B) when space within a...

The percentage increase in magnetic field (B) when space within a current carrying solenoid is filled with magnesium (magnetic susceptibility χmg=1.2×10−5)\left.\chi_{\mathrm{mg}}=1.2 \times 10^{-5}\right) is :

Options

  1. A65×10−3%\frac{6}{5} \times 10^{-3} \%
  2. B56×10−5%\frac{5}{6} \times 10^{-5} \%
  3. C56×10−4%\frac{5}{6} \times 10^{-4} \%
  4. D53×10−5%\frac{5}{3} \times 10^{-5} \%

Correct answer

A. 65×10−3%\frac{6}{5} \times 10^{-3} \%

Step-by-step solution

% change in  B=Bnew −Bold Bold ×100%=μni−μ0niμ0ni×100%=(μ−μ0)μ0×100%=(μ0μr−μ0)μ0×100%=(μr−1)×100%=χn×100%=1.2×10−3%\begin{aligned} & \% \text{ change\text{ in } } B=\frac{B_{\text{new }}-B_{\text{old }}}{B_{\text{old }}} \times 100 \% \\ & =\frac{\mu \mathrm{ni}-\mu_0 \mathrm{ni}}{\mu_0 \mathrm{ni}} \times 100 \%=\frac{\left(\mu-\mu_0\right)}{\mu_0} \times 100 \% \\ & =\frac{\left(\mu_0 \mu_{\mathrm{r}}-\mu_0\right)}{\mu_0} \times 100 \% \\ & =\left(\mu_{\mathrm{r}}-1\right) \times 100 \% \\ & =\chi_{\mathrm{n}} \times 100 \% \\ & =1.2 \times 10^{-3} \%\end{aligned}
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