According to Laplace's Law of Magnetic Circuits, the magnetic field strength H in a core is directly proportional to the magnetomotive force (MMF) and inversely proportional to the length of the magnetic path. If the MMF is increased by a factor of 2, and the length of the magnetic path is halved, what will be the change in the magnetic field strength H?

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RRB JE ECE 22 Apr 2025 Shift 1 CBT 2 Official Paper

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Answer 1

Concept:

According to Laplace's Law for Magnetic Circuits, the magnetic field strength H is given by:

\( H = \frac{\text{MMF}}{l} \)

Where:

Given:

MMF is increased by a factor of 2 → \( \text{MMF}_{\text{new}} = 2 \cdot \text{MMF} \)

Length is halved → \( l_{\text{new}} = \frac{l}{2} \)

Calculation:

\( H_{\text{new}} = \frac{2 \cdot \text{MMF}}{l/2} = \frac{2 \cdot \text{MMF} \cdot 2}{l} = \frac{4 \cdot \text{MMF}}{l} = 4H \)

Conclusion:

Correct Answer: Option 4) It will increase by a factor of 4.