Magnetic effect of current– If current flows through a conductor setup magnetic field around it is first observed by Oersted in 1820 . After that Biot-savart established a formula for magnetic field due to small current carrying conductor. Direction of magnetic field can be found using right hand thumb rule . If current is flowing through st. line and thumb shows the direction of current flowing through it then curled finger gives the direction of magnetic field. If current flowing through a circular coil ,and curled finger shows the direction of current then thumbs gives the direction of magnetic field.