Horse Shoe Magnet

Plotting Mariner’s Compass for Physics Lab – Magnetic needle mounted in a circular dish, having printed scale at the inside of the bottom, fitted with glass on the top.
Diameter :
(a) 12mm
(b) 16mm
(c) 20mm
(d) 25 mm
(e) 38 mm
(f) 50 mm
(g) 75mm