Given, number of turns in the coil, w = 30
Current in the coil, / = 0.35A Radius of circular coil,
r = 12 cm = 0.12 m (i) Let N-S be the line of magnetic meridian, the coil is placed at an angle of 45° with the magnetic meridian the planes of coil. The needle point towards from West to East. The magnetic field produced due to the coil is B and the direction of magnetic field B is along the axis of coil, i.e. it makes an angle of 45° with East. The needle points towards from West to East only if the direction of magnetic field B is at an angle 45° from East.
Use the formula of magnetic field produced by a current carrying coil,
As the direction of current in the coil is reversed and the coil is turned by 90° anti-clockwise, the direction of needle will reverse, i.e. it points from East to West.