Electric fields are produced by charges. Charges may be one of two signs, positive or negative. Changing the positions of positive and negative charges can alter an electric field. An electric field is a vector quantity from which the magnitude and direction of an electric force is determined. The electric force is due to the presence of charged particles. Charge is the attribute of matter by which matter responds to electromagnetic forces. Charge is responsible for all electrical phenomena. Charges are either positive or negative.
In Equation 1, w stands for work, q stands for charge, is Coulomb’s constant, r stands for distance from a charge, and stands for the distance over which work is done. The EM Field program was used to study the effects of charges on electric fields. Procedure and Data The program EM Field was opened. Sources was clicked, and 3D Point Charges was selected. Then Display was clicked, and Show Grid was selected. In EM Field, a +1 charge was dragged to the middle of the grid. Field and Potential was clicked, and Field Vectors was selected. This showed the electric field vectors associated with the +1 charge when clicking randomly on the screen.
The screen was clicked at different intervals along the x-axis to see how the magnitude of the vector changed as the distance from the charge changed. The vectors pointed away from the positive charge, and the magnitude increased as the charge was approached. The +1 charge was replaced with a -1 charge, and the process of clicking around the screen to see the effect of distance on the vectors was repeated. Screenshot 1 was taken and shown below. The vectors pointed toward the negative charge, and the magnitude increased as the charge was approached. The -1 charge was replaced with a +2 charge.
The process of clicking around the screen to see the effect of distance on the vectors was repeated. Screenshot 2 was taken and shown below. The vectors pointed away from the positive charge, and the magnitude increased as the charge was approached. The grid was cleared and a +1 charge was placed in the center of the screen. Field and Potential was clicked, and Field Lines was selected. The screen was clicked in random places a few times. Field and Potential was clicked and Field Vectors was selected. Then the field lines around the charge were clicked. Screenshot 3 was taken and shown below.
The vectors were tangential to the field lines. The grid was cleared and a +1 charge was added with a -1 charge two boxes away. Field Lines were drawn around each charge. Then several field vectors were added along the field lines. Screenshot 4 was taken and shown below. The field pointed toward the negative charge. The lines did not overlap. If a positive test charge was placed inside the electric field, it would follow the field lines toward the negative line. The grid was cleared, and a +1 charge was added on the screen with another +1 charge two boxes away.
Field lines were drawn around each charge, and several field vectors were added along the field lines. Screenshot 5 was taken and shown below. The field points away from both positive charges. The field lines do not overlap. If a positive test charge were placed inside the electric field, it would follow the electric field lines away from the two positive charges. File was clicked and Get charges or currents from file was selected. Then qplates. emf was selected. Several field lines were ween the two charged plates. Field vectors were randomly placed inside and outside of the plates.
Screenshot 6 was taken and shown below. The field lines between the two rows go toward the negative charges. If the field lines are outside the two rows, they go around the outside of the rows and toward the negative charges. The field lines do not overlap. If a positive test charge were placed inside the electric field, it would follow the electric field lines away from the two positive charges. EM Field was exited and then reopened. Sources was clicked and 3D Point Charges was selected. Display was clicked and Show Grid was selected. A +4 charged was added to the grid. Several field lines were added at arbitrary points.
The Field and Potential button was clicked and Equipotentials with number was selected. The screen was clicked from box 1 to box 6 at 1 box intervals. Several field vectors were added along the equipotental lines. Screenshot 7 was taken and shown below. Vectors that were placed on the same field line have the same direction, but the magnitude gets smaller the farther the vector is from the charge Conclusion Field vectors point away from positive charges and toward negative charges; the magnitude of the field vectors increase as positive or negative charges are approached.
The magnitude of the field vectors also increase as the magnitude of the charge increases. Vector field lines are tangential to the field lines. If a positive test charge that was free to move was placed inside an electric field, it would follow the field lines toward the negative charge or away from the positive charge. If there is a row of negative charges and a row of positive charges, the field lines between the two rows go toward the negative charges. If the field lines are outside the two rows, they go around the outside of the rows and toward the negative charges.
Field lines never overlap. Vectors that were placed on the same field line have the same direction, but the magnitude gets smaller the farther the vector is from the charge. If an imaginary charge was placed on an equipotential line, if it moves with the line, the work would not be zero. This can be determined because the dot product in Equation 1 between and would not be zero. If the charge moved perpendicular to the line, the work would be zero. This can be determined because the dot product in Equation 1 between and would be zero.
