A circular coil of radius 20 cm and 20 turns, is mounted vertically with its plane in the magnetic meridian. A small magnetic needle (free to rotate about vertical axis) is placed at the centre of the coil. It is deflected through 45 o when a current passes through the coil and is in equilibrium (Horizontal component of earth's field is B H = 0.34 × 10 − 4 T ). The current in the coil is

Question

A circular coil of radius 20 cm and 20 turns, is mounted vertically with its plane in the magnetic meridian. A small magnetic needle (free to rotate about vertical axis) is placed at the centre of the coil. It is deflected through 45 o when a current passes through the coil and is in equilibrium (Horizontal component of earth's field is B H = 0.34 × 10 − 4 T ). The current in the coil is, 1 7 1 0 π A, 6 A, 6 × 10 − 3 A, 3 5 0 A

MARKS App · Accepted Answer

WWe know magnetic field due to coil B = μ 0 Ni 2 r The needle is in equlibrium , B H tan θ = μ 0 Ni 2 r the current in the coil , i = 0.34 × 1 0 - 4 × 2 × 0.2 4 π × 1 0 - 7 × 2 0 = 1 7 1 0 π A

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