State Biot-Savart law.Use it to derive an expression for the magnetic field at the centre of a circular loop of radius R carrying a steady current I.Sketch the magnetic field lines for such a current carrying loop.

iot-Savart law states that the magnetic field dB due to the current element dl at any point P is

(i) directly proportional to the current I, dB I

(ii) directly proportional to the length dl of the element, dB dl

(iii) directly proportional to sin, whereis the angle between dl and r, dB sin

(iv) inversely proportional to the square of the distance r from the current element AB,

From (i), (ii) , (iii), and (iv), we obtain

At centre, x = 0