Download Self Induced Current - General Physics - Solved Past Paper and more Exams Physics in PDF only on Docsity! 1. (25 pts) a) (5 pts) The current in a circuit is flowing clockwise and is increasing. In what direction is the self-induced current in this circuit? E = −L dI dt So the induced potential opposed the changing current. If the current is increasing, then the in- duced potential produced a current in the opposite direction. In this example, the opposite direction is counter-clockwise. b) (5 pts) Visiting a new planet, an astronaut observes that the needle of a compass (that is able to swing freely in three-dimensions) settles down to pointing a little up and to the left. In what direction is the magnetic field at this location? We defined the direction in which a magnetic field points as the direction in which the needle of a compass points at that location. Since the needle of this compass is pointing a little up and to the left, the direction of the magnetic field must be a little up and to the left. c) (5 pts) According to the most current (and most accurate) theory, light is composed only of particles and not waves. Why, then, do we continue to teach and use the wave theory of light? Since the wave theory of light is unable to account for all of the properties of light, we know that it is not true. In other words, the wave theory has been disproven! But we still teach it because it can be used to get good predictions for a lot of the properties of light and it is much more mathematically simple than Quantum Electrodynamics, the current theory. d) (5 pts) Plane polarized light with the electric field oscillating horizontally is incident on a linear polarizer with the transmission axis rotated 25◦ counter-clockwise from horizontal (when looking into the beam). Describe the polarization of the electric field that is transmitted through the polarizer, if any. (Is it still linear? If so, in what direction? Is it polarized some other way? Is any transmitted at all?) Only a fraction of the incident electric field will be transmitted, but some will be transmitted. The portion transmitted will be linearly polarized parallel to the transmission axis of the polarizer: at 25◦ CCW from horizontal. e) (5 pts) Can there be a case where the magnetic field through a loop and the magnetic field produced by the induced current in the loop are in the same directions, even though Lenz’s Law insists that the induced current oppose the changing flux? If the magnetic flux is decreasing, then the magnetic field from the induced current will be in the same direction as the “external” magnetic field. So the answer to this problem is yes.
