A Long Vertical Wire Carries a Steady 70 a Current

question 32

Multiple Choice

A long vertical wire carries a steady 70 A current. As shown in the figure, a pair of horizontal rails are 0.20 m apart. A 20-Ω resistor connects points a and b, at the end of the rails. A bar is in contact with the rails, and is moved by an external force with a constant horizontal velocity of 0.90 m/s to the right, as shown. The bar and the rails have negligible resistance. At the instant that the bar is 0.20 m from the wire, what are the induced current in the resistor and its direction through the resistor? (μ₀ = 4π × 10^-7 T ∙ m/A)

• A)0.63 μA, from a to b
• B)0.63 μA, from b to a
• C)0.32 μA, from a to b
• D)0.32 μA, from b to a
• E)1.9 μA, from b to a

---

Definitions:

Ribs

A series of curved bones that form the protective cage around the chest, supporting the upper body and protecting vital organs.

Sternoclavicular Joint

The joint connecting the clavicle (collarbone) to the sternum (breastbone) at the base of the neck.

Manubrium

The broad upper part of the sternum, with which the clavicles and the first two ribs articulate.

Clavicle

A long bone that serves as a strut between the shoulder blade and the sternum or breastbone.