2. (5 points) In magnetic property measurement, we need to correct an applied field to a true field. Which one is a correct true field? (a) Hự = Ha +

Ha, (b) Hµ = Ha - N¼M, (c) Hu = Ha - nHd, and (d)Hr = Ha - (T/2)Ha. (Ha = demagnetization field (=NaM). Ha = applied field. Hr = true field)