Grade 11 Physics – Electric Fields

  • All matter is made up of:
  • Atoms are made of:

Charged Atoms:

  • Atoms are normally ______
  • When an atom loses electrons, it becomes ______charged
  • When an atom gains electrons, it becomes ______charged

The Law of Electric Charges

  • Opposite electric charges ______each other
  • Similar electric charges ______each other
  • Charged objects attract some ______objects

Methods of Charging objects




Types of Materials



Gravitational Fields ()

A Gravitational field is the region of space around a mass where another mass experiences an attractive force. It can be calculated by:

The Earth’s gravitational field is 9.8N/kg [down].

Representing Fields

Field Lines can be used to represent the strength and direction of a field.

Properties of Field Lines:

  1. Lines must be drawn ______to the object.
  2. The further apart the lines are, the ______the field is.

The gravitational field lines for the Earth show the direction any object would feel a force in the space around the Earth.

Electric Fields ()

An electric field is the region of space around a charge where a positive charge experiences a force.

Electric field lines can be used to represent the strength and direction of an electric field. The direction of the electric field lines are determined by the direction a positive charge would feel a force when placed in the electric field.

Properties of Electric Field Lines:

  1. The field lines begin at the object producing the field and are drawn
    ______to it.
  2. Field lines point in the direction a ______would
    experience a force
  3. The further apart the lines are, the ______the field is.

Units of Electric Charge

Two different units will be used for the charge on an object.

  1. Elementary Charges (ec): the basic unit of charge. It tells you the number of electrons that have been transferred to or from an object.
    1 electron = ______
    1 proton = ______
  2. Coulombs (C): usually a large amount of electrons will be transferred to or from an object, so when an answer in elementary charges will be very large. One Coulomb is a large number of electrons:
    1 C = 6.25 x 1018ec and 1ec = 1.6 x 10-19C

Remember: an object becomes charged when there is a transfer of electrons. Only whole number of electrons can be transferred to or from an object. This means there cannot be a charge of –1.5ec or +4.882ec.
When calculating the number of elementary charges, if you get a fraction of an electron, always round down your answer.
Example: an answer of +4.882ec should be rounded to +4ec

Calculating the Strength of an Electric Field ()

The strength of an electric field can be determine by:

To determine the direction of the electric field, imagine placing a test charge (an extremely small imaginary positive charge) near the charge that is creating the field and think about the direction that test charge would feel a force.

Unit Conversion

When calculating the electric field strength it is important that the units are all the same. This will require converting units to and from Elementary Charges and Coulombs. Either conversion factor (1 C = 6.25 x 1018ec OR 1ec = 1.6 x 10-19C) can be used.

Example: Convert 0.0015C to ec.

Example: Convert 4000N/C to N/ec.

Example: Convert 3.25 x 10-15N/ec to N/C.

K. Byrnes
PHY30S