A coil of wire of cross-section 0.50 mm2 weighs 75g in air and 65g in water. The length of the coil in cm is

Area =πr2=0.50mm2=0.0050 cm2 Let L be its length. So volume, V = 0.0050L cm3 Weight in air, Wa=75g Weight in water, WW=65g So buoyant force of water=Wa−WW=10g = V ×density of water ×g or 10=0.0050L×1 L=100.0050=10×10450=10550cm