IB HL Physics Electric Field in a Moving Conductor

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A conductor moves in a magnetic field. Is the electric field in the conductor zero? A tutorial sheet follows.

  1. State Ohm's law in terms of electric field (E) and current density (J).
  2. A current flows through a stationary conductor that obeys Ohm's law. Is there an electric field inside the conductor? Outside of the conductor?
  3. A straight metal rod of length L is a perfect conductor (zero resistance). The rod moves at a constant velocity v along the x-axis through a uniform magnetic field B along the z-axis. The length of the rod is along the y-axis. Find the electric field in the rod in the (a) reference frame of the laboratory, (b) reference frame of the rod.
  4. In the previous question find the force acting on a charge q in the rod relative to the reference frame of the rod.
  5. In question 3 the rod has a constant non-zero resistance. Find the force on a charge q in the rod relative to the reference frame of the rod.

IB Physics Work Done on a Moving Charge in a Magnetic field

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A common question is finding the work done on a charge as it moves in a magnetic field. Is it always zero? A tutorial sheet of questions investigates this concept.

  1. A constant, uniform magnetic field B acts along the x-axis. A charge q enters the field at a velocity v at an angle 𝜃 to the x-axis. Is work done on the moving charge?
  2. A constant current flows along a long straight wire that is along the x-axis. At a certain instant a charge q is moving along the x-axis at a speed v towards the wire. Is work done on the charge?
  3. A magnetic field increases at a rate proportional to the time, B = kt, and its direction is parallel to the x-axis. Does the magnetic field do work on the moving charge in question 1? Does the associated electric field do work on the moving charge?