Question

A magnetic field, strength 3T, has a direction out of the page. A loop of wire sits in the field and on the plane of the page (area vector of loop is out of page). The loop is much smaller than the extent of the field. The magnetic field starts to slowly change at a rate of -0.0001T/s. Looking down on the loop, which statement is correct?

A. Magnetic flux out of page decreasing; anti-clockwise current induced in loop

B. Magnetic flux out of page increasing; clockwise current induced in loop

C. Magnetic flux out of page decreasing; clockwise current induced in loop

D. Magnetic flux out of page increasing; anti-clockwise current induced in loop

Amy is standing on the positive x-axis, 2 m from the origin. River is standing on the positive y-axis, 2m from the origin. A charge moves at a high speed from left to right along the x-axis, and Amy and River measure the magnetic field when the charge passes through the origin. Which statement is true about the strength and direction of the magnetic fields that they measure? Take the +z-axis to be in a direction out of the page, when the x- and y-axis are in the plane of the page.

A. Amy: strength of magnetic field = 0; River: strength of magnetic field = 0Please give a thorough explanation for each

B. Amy: strength of magnetic field = 0; River: stength of magnetic field >0 and in +z direction

C. Amy: strength of magnetic field =0; River: strength of magnetic field >0 and in -z-direction

D. Amy: strength of magnetic field >0 and in +z-direction; River: strength of magnetic field =0

Two parallel wires carry currents in opposite directions. Wire 1 has a current of 12A, and Wire 2 has a current of 6A. What is the ratio of the magnetic force on Wire 1 to the magnetic force on Wire 2?

A. 1

B. 2

C. 4

D. 1/2

Under what circumstances is a current NOT induced in a coil of wire?

A. A magnet is held stationary near to the coil
B. A current carrying coil is moved rapidly towards the coil.

C. A magnet is moved rapidly towards the coil.

D. A magnet is moved rapidly away from the coil.

Answer 1

1)B (When the magentic field is in upward direction, then the current here will move in clockwise direction, and the flux incduced will be in opposit direction

so, e =-Ndfi/dt =-N(-d@/dt) =Nd@/dt therefore the agnetic flux out of page increasing; clockwise current induced in loop.

2)B (Amy: strength of magnetic field = 0; River: stength of magnetic field >0 and in +z direction)

3)A (because the force acting on the two wires will be the same then the ratio becomes =1)

4)A (When the magnet is held stationary then there will be no induced emf then automatically there will be no current induced in the coil)