The Physics
Opus in profectus

Electromagnetic Force

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  1. Write something.
  2. Write something.
  3. Write something.
  4. Write something completely different.


  1. How does the direction of a magnetic force on a moving charged particle differ from the direction of an electric force? State the direction of each force relative to the respective field.
  2. Describe the path of a charged particle in a uniform magnetic field if its velocity is…
    1. parallel to the magnetic field
    2. perpendicular to the magnetic field
    3. at an angle to the magnetic field that is neither parallel nor perpendicular
  3. This is an experiment that you can try at home if you have an old TV or computer monitor. Take a strong magnet and hold it up to a CRT display.
    1. Why does the image become distorted?
    2. Why is the image covered with colored bands of red, green, and blue?
    3. Why does the color stay screwed up after the magnet is removed?
    4. Why does the color return to normal after the television has been turned off and back on?
    5. Why doesn't this effect occur with LED, LCD, and plasma displays?
  4. Show the direction of the force acting on the current-carrying wire between the two bar magnets.

    South pole on the left, north pole on the right, wire in between with an arrow indicating current down

  5. Determine the direction of the force acting on the electron moving between the poles of a horseshoe magnet.

    Drawing of an electron with an x on it between the poles of an upright horseshoe magnet

  6. Manipulated photo of particle tracks
    The tracks highlighted in the photograph on the right were made by subatomic particles in a collider. The tracks highlighted in red and green were made by electrons.
    1. How are the tracks made by the electrons different from the other tracks? Why are they different?
    2. How is the track highlighted in red different from the track highlighted in green? Why is it different?
  7. A positively charged particle is placed at rest in a region of uniform electric and magnetic fields. Describe…
    1. the direction of the electric and magnetic forces just before the particle starts moving
    2. the resulting path of the charge

    if the two fields are…


  1. Three successive electromagnetic experiments are performed on an electron beam as shown in the diagram below. (Ignore the effects of gravity in this problem.)

    Cartoon representation

    1. The beam enters region a with negligible initial velocity and is accelerated across a potential difference of 10,000 V in a distance of 10 cm. Determine…
      1. the magnitude of the electric field in this region
      2. the net force on the electrons in this region
      3. the final speed of the electrons when they exit this region
    2. The beam then passes into region b where there are both electric and magnetic fields. The electric field strength in region b has the same magnitude as region a but points downward. The magnetic field points inward and is adjusted so that the magnetic and electric forces on the electron beam cancel. Determine…
      1. the magnitude of the magnetic field in this region
    3. The beam finally enters region c, where there is a magnetic field but no electric field. The electrons follow a semicircular path with a radius of 7.5 cm. Determine…
      1. the magnitude and direction of the magnetic field in this region


  1. Three problems about electromagnetic units…
    1. Show that the units in this expression (μ0 = 4π × 10−7 T m/A) are equivalent to the units in this expression (μ0 = 4π × 10−7 N/A2) for the permeability of free space.
    2. Express the permeability of free space in terms of funamental units.
    3. Reduce the tesla to its equivalent in SI base units.