Table 24.1 shows that the strength of the magnetic field 1 cm from a wire carrying a 10 A current is 4 times the earth's field. Referring to Figure 24. 18 for guidance, at what distance from the wire will the field equal that of the earth?

A. 2cm B. 4cm C. 8cm D. 16 cm

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TABLE 24.1 Typical magnetic field strengths Field source and location 10 cm from a wire with 1 A current Field strength (T) 2 x 10 Surface of the earth 5 x 10-5 1 cm from a wire with 10 A current 2 x 104 Refrigerator magnet 5 10 3 100-turn coil, 1 cm diameter, with 1 A current 1 X 10-2 Surface of the sun, in a sunspot 1 X 10-1 Near a rare-earth magnet 1 MRI solenoid 1