If a long wire carrying current is going into the page of the two loops, what force would it require? Why is the answer 0 and why is the angle 180 degrees, and not 90 degrees.

A solenoid has length L, total number of turns N and current I. What happens to the magnitude of the magnetic held (B) inside the solenoid if the number of turns is doubled, with the length and current remaining the same? It becomes four times larger. It becomes one-fourth as large. It is unchanged. O It becomes one-half as large. O It becomes twice as large.

Two coplanar and concentric circular loops of wire carry currents of I, = 5.90 A and I, = 2.30 A in opposite directions as in the figure below. Let r, = 12.0 cm and r, = 8.60 cm. (Assume the positive direction along the axis perpendicular to the faces of the loops is out of the screen (towards you) and assume the positive vertical direction is toward the top of the screen.) (a) What is the magnitude of the net magnetic field (in µT) at the center of the two loops? PT (b) What is the direction of the net magnetic field at the center of the two loops? out of the screen O into the screen O toward the top of the screen O toward the bottom of the screen (c) Let r, remain fixed at 12.0 cm and let r, be a variable. Determine the value ofr, (in cm) such that the net field at the center of the loops is zero. cm

A battery is connected to wires that hand vertically (gravity acts down in the diagram).  Hooks at the ends of the wires hold a horizontal copper bar (the thick bar) of mass 0.6 kg and length 0.5 meters.  Another apparatus (not shown) can create a uniform magnetic field in the region of space given by the dashed rectangle.  The total resistance of the circuit is 1.20 Ohms and the battery supplies 24 Volts.  The magnetic field can be adjusted in strength until the bar lifts off of the hooks and levitates magnetically – not moving just above the hooks as shown. a) Determine the necessary direction of the magnetic field in the dashed rectangle. b) Calculate the required magnitude of the magnetic field.