Question

1. At a certain moment in time, two identical, positively charged particles are flying horizontally toward each other. Let the xx-axis be the axis along which the particles are moving, and let the origin lie directly between both particles. Let the yy-axis be oriented pointing vertically up and the zz-axis point directly out from the origin.
   
   1) Which combination of options below are the best combination of corrections that you might make to your friend's diagram? [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE"]
   
   A) The particles exert magnetic forces on each other.
   B) The magnetic fields of each particle reinforce each other at positions equidistant from each of the particles.
   C) The total magnetic field at points vertically above the positive xx-axis point in the positive zz direction.
   D) The total magnetic field at points vertically below the negative xx-axis point in the negative zz direction.
   E) None of the above
2. A circular loop of wire has current flowing through it. You are looking straight down at this loop from above. The flow of the current through the loop relative to you can be either clockwise or counter-clockwise around the loop. The options describe a series of experiments involving either a magnet or another current loop brought down toward the original. The current in the original loop can be changed between experiments. Choose the combination of options below are physically consistent. [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE"]
   
   A) A magnet's south pole is repelled as it is brought down to the loop from above. Therefore, the current flows clockwise.
   B) A magnet's north pole is repelled as it is brought down to the loop from above. Therefore, the current flows counter-clockwise.
   C) A counter-clockwise current loop above the original is attracted. Therefore, the current flows clockwise.
   D) A clockwise current loop above the original is repelled. Therefore, the current flows counter-clockwise.
   E) None of the above
3. Two positively charged particles are travelling through space in each others' vicinity. Using the standard xx-yy-zz coordinate grid, particle 1 travels along the positive xx direction while particle 2 travels along the positive yy direction, heading directly for the first particle from below.
   
   Which combination of options below are the most accurate combination of statements. [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE"]
   
   A) Particle 1's magnetic field at particle 2's location points in along the zz-axis.
   B) Particle 2 feels a magnetic force pushing down the negative yy direction.
   C) Particle 2's magnetic field at the location of particle 1 is zero.
   D) Particle 1 feels no magnetic force due to particle 2's magnetic field.
   E) None of the above
4. An electric motor is a device that transfers electrically stored energy into kinetic energy. A very crude one would consist of a conducting wire shaped as a loop with a steady electric current passing through it placed in a uniform magnetic field. Let's imagine that the magnetic field is directed along the positive xx-axis, which we'll set up as going from left to right. The yy-axis points up and the zz-axis points out. Assume an absence of any frictional effects.
   
   Which combination of options below are the most accurate combination of statements? [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE"]
   
   A) If the current loop's dipole moment is initially aligned with the field, there will be no resulting rotational motion.
   B) Maximum potential energy in this system occurs when the dipole moment points in the −i^−i^ direction
   C) If the dipole moment initially points along the k^k^ direction, it's left end will feel a force pushing up along the j^j^ direction.
   D) If the dipole moment initially points along the k^k^ direction, it's right end will feel a force pushing in along the −k^−k^ direction.
   E) None of the above
5. An electron gun sends out a beam of electrons whose kinetic energies are all about 54 μμeV. (1 μeV=1.6×10−25 J1 μeV=1.6×10−25 J.) You need to set up a magnetic field perpendicular to the beam that causes it to turn through a 90∘∘ circular arc of length 2 mm. How strong must the magnetic field be?
6. You take a wire and wind it into a circular loop (leaving the two ends free so that they can be connected to a power supply). You take a longer wire and wind it around making 6 turns of the same radius as your first single loop. If you run the same amount of current through both wires, compare the magnetic dipole moment magnitudes of the two setups. What is the ratio of the multi-loop current's dipole moment magnitude to that of the single loop current?
7. Two particles, both carrying charge 6 C are traveling parallel to each other with velocities of v⃗ =12000i^v→=12000i^ in m/s. They are positioned at the points (0,2,0)(0,2,0) and (0,−2,0)(0,−2,0). What is the magnitude and direction of the magnetic field at (0,2,0)(0,2,0) due to the particle located at (0,−2,0)(0,−2,0)? [Enter the magnitude in answer box 1 and the direction as one of either "in", "out", "up", "down", "left", or "right" in answer box 2. Assume that the xx-axis corresponds to left/right, the yy-axis corresponds to up/down, and the zz-axis corresponds to in/out.]
8. What is the force exerted by the magnetic field you calculated above on the particle at that location? Compare this to the direction of the electric force on the particle. [Enter the magnitude of the force in the first answer box and its direction in the second. Enter the direction of the electric force on the particle in the third box. For the directions enter either "in", "out", "up", "down", "left", or "right"]
9. How fast would the particles have to travel in order for there to be a balance between the magnetic and electric forces they exert on each other?
10. Geordi La Forge was born blind, but has a VISOR that allows him to perceive a broad range of the electromagnetic spectrum. Let's suppose that there's a setting that allows Geordi to distinguish electric and magnetic fields from one another. The VISOR also gives him readings on voltage differences between various points in space. If Geordi were to walk by a uniform magnetic field that was not moving relative to the ground, what would he see?
    
    Choose the best combination of options below. [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE"]
    
    A) Identical magnetic field vectors at every point in space.
    B) There would only be magnetic field vectors since their are no electric field sources.
    C) Non-zero voltage differences along displacements perpendicular to the magnetic field vectors.
    D) Non-zero voltage differences along displacements parallel to the magnetic field vectors.
    E) None of the above
11. A loop of copper (a conducting material) is carried across a region of space with a non-zero uniform magnetic field so that the area surrounded by the loop is perpendicular to the field direction. Imagine the situation is oriented so that the magnetic field is coming out of the screen toward you, and the loop is being pulled toward the right.
    
    Which combination of options below is most accurate? [Enter your answer as a string of the letter options you believe are correct. For instance, if you think options A, D, and E are correct, then enter "ADE"]
    
    A) The magnetic flux through the loop is decreasing.
    B) The induced current flows clockwise.
    C) Nothing would be changed if the field were not uniform.
    D) Turning the loop around would induce a current.
    E) None of the above

Answer 1

At a certain moment in time, two identical, positively charged particles are flying horizontally toward each other. Let the xx-axis be the axis along which the particles are moving, and let the origin lie directly between both particles. Let the yy-axis be oriented pointing vertically up and the zz-axis point directly out from the origin.

A charged particle moving , makes a current I = dq/dt = qv. The magnetic field is perpendicular to the direction of velocity CCW. Field from each particle is opposite in direction. The resultant field magnitude is the difference of the two.

CD

A circular loop of wire has current flowing through it. You are looking straight down at this loop from above. The flow of the current through the loop relative to you can be either clockwise or counter-clockwise around the loop. The options describe a series of experiments involving either a magnet or another current loop brought down toward the original. The current in the original loop can be changed between experiments.

CW current loop is equal to a bar magnet with south pole up, magnetic field is downward. south pole repels and north pole attracted.

AB

Two positively charged particles are travelling through space in each others' vicinity. Using the standard xx-yy-zz coordinate grid, particle 1 travels along the positive xx direction while particle 2 travels along the positive yy direction, heading directly for the first particle from below.

As explained earlier a moving charged particle produces magnetic field around it. magnetic field from 1 is in zz -direction. magnetic force on the 2nd particle is in xx direction ( vXB) . The same is true of the for the magnetic field of 2 at 1. Both influence each other.

A

An electric motor is a device that transfers electrically stored energy into kinetic energy. A very crude one would consist of a conducting wire shaped as a loop with a steady electric current passing through it placed in a uniform magnetic field. Let's imagine that the magnetic field is directed along the positive xx-axis, which we'll set up as going from left to right. The yy-axis points up and the zz-axis points out. Assume an absence of any frictional effects.

magnetic field along xx -axis , dipole is aligned with field, like poles repel and the coil rotates. when the dipole is aligned with -i,-i , the potential energy is minimum. when the dipole is aligned in kk direction. it will experience a force in -kk direction

D