20. An emf of 12.0 mV is induced in a 500 turn coil when the current is changing at a rate of 10.0 A/s. What is the magnetic flux through each turn of coil at the instant when the current is 3.00 A? (A) 1.4 × 10⁻⁶ T·m² (B) 2.2 × 10⁻⁶ T·m² (C) 5.4 × 10⁻⁶ T·m² (D) 7.2 × 10⁻⁶ T·m² (E) 8.8 × 10⁻⁶ T·m²

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

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