ELECTRIC FIELD MOD 2

• Electric field lines are series of lines drawn from a point charge representing the magnitude and direction of force exerted by that charge.
• Electric field lines are used to visualize and analyze electric fields.
• The closeness of the lines is directly related to the strength of the electric field. If a test charge placed anywhere will feel a force in the direction of the field line; this force will have a strength proportional to the density of the lines.
• The electric field is defined for a positive test charge q, so that the field lines point away from a positive charge and toward a negative charge.
• The electric field is defined for a positive test charge q, so that the field lines point away from a positive charge and toward a negative charge.
• The total electric field created by multiple charges is the vector sum of the individual fields created by each charge.
• The total electric field created by multiple charges is the vector sum of the individual fields created by each charge.
• 1. Field lines must begin on positive charges and terminate on negative charges.
  2. The number of field lines leaving a positive charge or entering a negative charge is proportional to the magnitude of the charge.
  3. The strength of the field is proportional to the closeness of the field lines—more precisely, it is proportional to the number of lines per unit area perpendicular to the lines.
  4. The direction of the electric field is tangent to the field line at any point in space.
  5. Field lines can never cross. This means that the field is unique at any point.
• Earth is an example of a uniform electric field with approximately 150 N/C that is directed downward, with the magnitude increasing slightly as it gets closer to the surface.
• At around 100 km above the surface of Earth is a layer of charged particles called the ionosphere.
• In fair weather, the ionosphere is positive and the Earth is largely negative, maintaining the electric field.
• In storm conditions, clouds form and localized electric fields can be larger and reversed in direction. If the electric field is sufficiently large, the insulating properties of the surrounding material break down and it becomes conducting.
• For air, this occurs at around 3x10^6  N/C. Air ionizes ions and electrons recombine, and we get discharge in the form of lightning sparks and corona discharge.
• The aurora is formed from interactions between the solar wind streaming out from the sun and Earth's protective magnetic field, or magnetosphere.
• Auroras occur when charged particles collide with gases in Earth's upper atmosphere