TABLE 36.2 Relative Permeability, H, of Some Diamagnetic, Material Na cygan(s t.p.) permalloy: 79% Ni, 15% Fe Permendur: 49% Fe, 49% Ca, 2%6V Source: F Brailsford, Physical Principles of Magnetism, London: Van Nos- and, 1966. With permission. (b) FIGURE 36.2 Hall effect. A magnetic field B applied to a block of semiconducting material through which a current I is flowing exerts a force F=VX B on the current carriers(electrons or holes)and produces an electric charge on the right face of the block. The charge is positive if the carriers are holes and negative if the carriers are electrons Time-Varying Magnetic Fields In 1831, 11 years after Oersted demonstrated that a current produced a magnetic field which could deflect a compass needle, Faraday succeeded in showing the converse effect-that a magnetic field could produce a current. The reason for the delay between the two discoveries was that it is only when a etic field is anging that an emf is produce dΦ e 2000 by CRC Press LLC© 2000 by CRC Press LLC Time-Varying Magnetic Fields In 1831, 11 years after Oersted demonstrated that a current produced a magnetic field which could deflect a compass needle, Faraday succeeded in showing the converse effect—that a magnetic field could produce a current. The reason for the delay between the two discoveries was that it is only when a magnetic field is changing that an emf is produced. TABLE 36.2 Relative Permeability, mr , of Some Diamagnetic, Paramagnetic, and Ferromagnetic Materials Material mr Ms , A/m2 Diamagnetics Bismuth 0.999833 Mercury 0.999968 Silver 0.9999736 Lead 0.9999831 Copper 0.9999906 Water 0.9999912 Paraffin wax 0.99999942 Paramagnetics Oxygen (s.t.p.) 1.000002 Air 1.00000037 Aluminum 1.000021 Tungsten 1.00008 Platinum 1.0003 Manganese 1.001 Ferromagnetics Purified iron: 99.96% Fe 280,000 2.158 Motor-grade iron: 99.6% Fe 5,000 2.12 Permalloy: 78.5% Ni, 21.5% Fe 70,000 2.00 Supermalloy: 79% Ni, 15% Fe, 5% Mo, 0.5% Mn 1,000,000 0.79 Permendur: 49% Fe, 49% Ca, 2% V 5,000 2.36 Ferrimagnetics Manganese–zinc ferrite 750 0.34 1,200 0.36 Nickel–zinc ferrite 650 0.29 Source: F. Brailsford, Physical Principles of Magnetism, London: Van Nos￾trand, 1966. With permission. FIGURE 36.2 Hall effect. A magnetic field B applied to a block of semiconducting material through which a current I is flowing exerts a force F = V ¥ B on the current carriers (electrons or holes) and produces an electric charge on the right face of the block. The charge is positive if the carriers are holes and negative if the carriers are electrons. emf d d = - V F t