Try these "busters" to exercise your brain ... they should help you grasp the concepts underlying magnetic fields and charges, etc. To gain the maximum effect you should attempt to answer them before looking at the answers!
[1] Does a wire carrying a current exert a force on a magnet? Explain your reasoning.
[2] Can an electron that it stationary in a magnetic field be set into motion by the magnetic field? Compare and contrast the behavior of an electron in an electric field.
[3] A charged particle, passing through a certain region of space, has a velocity whose magnitude and direction remain constant. (a) If it is known that the external mmagnetic field is zero everywhere in this region can you conclude that the external electric field is zero also? (b) If it is known that the external electric field is zero everywhere, can you conclude that the external magnetic fiels is zero also? Explain your answers.
[4] Three paricles have identical charges and masses. They enter a magnetic field and follow the paths as shown below. Which particle is moving the fastest and which is moving the slowest.
[5] The drawing below shows a top view of 4 interconnected chambers. A negative charge is fired into chamber #1 and your job is to steer it through chambers #2, #3 and out the exit in #4. (a) Describe how the magnetic field in each of the chambers should be directed. (b) If the speed of the particle when in enters #1 is v, what is its speed when it exits #4? Explain your answer.
[6] The drawing shows a positively charged particle (+q) at the origin and a target in the third quadrant. A uniform magnetic field is directed into the plane of the paper. The charge can be projected in the plane of the diagram only and along the positive or negative x and y axes. Thus, there are only 4 possible initial trajectories. The particle can be made to hit the target using only two of the four possible directions. Work out which two they are and sketch the path of the particle.
[7] A positive charge is moving in a circular path under the influence of a magnetic field that is perpendicular to its motion:
If the velocity of the particle is reversed at some point along the path, does the particle retrace its original path? If not, why?
[8] A wire carries a current in a magnetic field as shown below:
If the wire is free to rotate, in which direction will it move? Explain your answer.
[9] A rectangular loop is placed in a uniform magnetic field with the plane of the loop pependicular to the direction of the field.
If a current flows through the loop as shown above, does the field exert a force and/or a torque on the loop? What will happen, if anything?
[10] A square coil is placed in a uniform magnetic field with its plane parallel to the field, as shown below.
If a current flows through the coil, as shown, does the field exert a force and/or a torque on the loop? What will happen, if anything?
[11] In a certain computer monitor, electrons are accelerated through a potential difference of 10,000V towards the screen. What is the maximum deflection the electrons experience if the Earth's magnetic field is 0.6G? Is it negligible?
[12] A moving charged particle enters a region where there is a "field" that deflects it, perpendicular to its motion. Can you offer two observations you might make that will confirm whether the "field" is an electric field or a magnetic field?
[13] A beam of negatively charged particles, moving from left to right, passes straight through a velocity selector, in which the electric field is upward. If the same particles were sent through in the opposite direction, what would happen?