MDCAT Electromagnetism MCQs

Sample Electromagnetism MCQs with answers

Try these questions, then open the answer to check your reasoning. Use the quiz above for more topics and a complete review.

1. Magnetic Field

   1. Magnetic field lines have a property that lines are ________________.

   1. A. Non intersecting
   2. B. Intersect near south pole
   3. C. Intersect near north pole
   4. D. Intersect everywhere
   View answer and explanation

   Answer: A. Non intersecting

   A fundamental property of magnetic field lines is that they never cross one another, because the tangent to a field line at any point gives the direction of the magnetic field there, and a field can have only one direction at a single point. If two lines intersected, the field would have two different directions at the intersection, which is impossible. Hence the correct choice is non intersecting, while the other options suggesting intersection near poles or everywhere are wrong.

2. Charged Particles

   2. If a particle's momentum doubles in the same perpendicular magnetic field, its orbit radius:

   1. A. halves
   2. B. quadruples
   3. C. doubles
   4. D. is unchanged
   View answer and explanation

   Answer: C. doubles

   Using $r=p/(|q|B)$, radius is directly proportional to momentum.

3. Magnetic Field

   3. Two long straight wires are set parallel to each other. Each carries a current i in the same direction and the separation between them is 2r. The strength of the magnetic field midway between them is

   1. A. ?oi/r
   2. B. 4?oi/r
   3. C. Zero
   4. D. ?oi/4r
   View answer and explanation

   Answer: C. Zero

   Keyword/Clue: midway between them and same direction current Concept/Formula: Magnetic field due to a long straight wire at distance d is $B=\mu {}_{0}i/(2\pi d).$ At the midpoint, distance from each wire is r. The fields from the two wires are equal in magnitude but opposite in direction (by right-hand rule), so they cancel: $B_{net}=B_1-B_2$ = 0. Why the Other Options Are Wrong: - Option A: Assumes fields add to a nonzero value; at the midpoint they cancel due to opposite directions. - Option B: Incorrect magnitude and still assumes addition rather than cancellation. - Option D: Uses an incorrect distance factor; also ignores that the two fields oppose each other.