15. At what distance from a long straight wire carrying a current of 5.0 A is the magnetic field due to the wire equal to the strength of the earth's field, 5.0 × 10⁻⁵ T? (A) 0.02 m (B) 0.2 m (C) 2 m (D) 20 m (E) 200 m

10. A copper telephone wire has essentially no sag between poles 35.0 m apart on a winter day when the temperature is -20.0°C. How much longer is the wire on a summer day when Tc = 35.0°C? Assume that the thermal coefficient of copper is constant throughout this range at its room temperature value. The average coefficient of linear expansion for copper is 17 × 10⁻⁶ (°C)⁻¹. (A) 3.27 cm (B) 4.12 cm (C) 1.00 cm (D) 12.04 cm (E) 8.40 cm

15. At what distance from a long straight wire carrying a current of 5.0 A is the magnetic field due to the wire equal to the strength of the earth's field, 5.0 × 10⁻⁵ T?
(A) 0.02 m
(B) 0.2 m
(C) 2 m
(D) 20 m
(E) 200 m

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