CUET · PHYSICS · PYQ PAPER 2025
The electric current in a circular coil of 3 turns produces a magnetic field \( B_1 \) at its centre. The coil is unwound and is rewound into a circular coil of 6 turns. Now on passing the same current, the magnetic field produced is \( B_2 \) at its centre. The ratio \( B_1 : B_2 \) is
- A \(1: 1\)
- B \(1: 2\)
- C \(1: 4\)
- D \(4: 1\)
Answer & Solution
Correct Answer
(C) \(1: 4\)
Step-by-step Solution
Detailed explanation
\( N_1 R_1 = N_2 R_2 \Rightarrow 3 R_1 = 6 R_2 \Rightarrow R_1 = 2 R_2 \) \( B = \frac{\mu_0 N I}{2R} \) \( \frac{B_1}{B_2} = \frac{\frac{\mu_0 N_1 I}{2R_1}}{\frac{\mu_0 N_2 I}{2R_2}} = \frac{N_1}{R_1} \cdot \frac{R_2}{N_2} \)…
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