Question

Problem 27.69 3 of 15 The rectangular loop of wire shown in the figure (Figure 1) has a mass of 0.11 g per centimeter of length and is pivoted about side ab on a frictionless axis. The current in the wire is 8.1 A in the direction shown Part A Find the magnitude of the magnetic field parallel to the y-axis that will cause the loop to swing up until its plane makes an angle of 30.0° with the yz-plane Express your answer using two significant figures Figure 1 of 1 Submit revious Answe equest Answer X Incorrect; Try Again; 5 attempts remaining 6.00 cm Part B Find the direction of the magnetic field parallel to the y-axis that will cause the loop to swing up until its plane makes an angle of 30.0with the yz-plane 0. 8.00 -y-direction cm +y-direction PreviOUS Answers

Answer 1

Part A

For the loop to swing upward, magnetic force on cd must be towards right as shown in the figure above. Thus magnetic field must be in the positive y-axis according to Flemings left hand rule. (If the middle finger represents the current from c to d, thumb represents the motion of the conductor (F_m), then fore finger represents the direction of magnetic field positive y axis)

Taking moments about ab, (Refer Side view diagram)

Sum of clockwise moments = sum of anticlockwise moments

(moment = force times perpendicular distance)

Thus the magnitude of the magnetic field is B = 1.34 x 10^-2 T

Part B

The direction of the magnetic field parallel to y-axis that will cause the loop to swing up until its plane makes an angle of 30^o with the yz plane.

Magnetic field must be in the positve y-axis according to Flemings left hand rule.

da - magnetic field is in the +z direction.

bc - magnetic field is in the -z direction.

ab is the pivot.