Question

define magnetic field lines?​

Answer 1

Your answer:-

The area surrounding a magnet, in which the force of the magnet can be detected, is said to have a magnetic field.

Answer 2

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Magnetic field lines are imaginary lines around the magnet. The magnitude of a field is indicated by its line's density. Near to South and North Pole of a magnet, the magnetic field is stronger and will get weaker when it moves away from the poles.

FORMULA OF MAGNETIC FIELD- The Biot-Savart Law can be used to determine the magnetic field strength from a current segment. For the simple case of an infinite straight current-carrying wire it is reduced to the form B=μ0I2πr B = μ 0 I 2 π r .