Purpose
The Electric Fields Interactive provides visual instruction on the electric field created by a configuration of point charges. Contours of the electric potential and the real-time motion of test charges can also be demonstrated.

Using the Interactive
Configure the interactive using the ADD CHARGES, CONTROLS, and WALL EFFECT sections on the right-hand side. The ADD CHARGES section is the most important of these three.

• Charge Slider bar: Sets the value of FIXED charges in the range -0.001 < q < +0.001 mC; determines the sign of TEST charges.
• Presets: Three preset configurations showing the motion of point charges. Select one and click PLAY.

Controls

• View Speed Slider bar: Controls the speed of the animation.
• Play/Step: PLAY animates the motion of test charges continuously; STEP animates the motion one time step per click.
• Reset: Removes charges from the screen.
• Show Grid: Displays the coordinate grid.
• Snap to Grid: Charges placed near a grid line will snap to the precise value of that line.

• No Walls: Moving test charges continue past the edge of the screen.
• Rubber: Moving test charges bounce off the edge of the screen elastically.
• Electrified: Edges of the screen are given a positive electric charge.

1			Select SHOW GRID and SNAP TO GRID and place a FIXED charge with q = -0.001 at the origin; deselect SHOW GRID. Note the direction of the electric field vectors and their relative lengths with increasing distance from the charge. Select TEST. Without clicking, move the test charge slowly from a corner of the screen in toward the fixed charge. Note the values of the potential and the electric field given in the lower left corner as you move closer to the charge. Move the test charge to an arbitrary position on the screen and click to set its position. Click PLAY to animate the motion of the test charge. Note how it moves. Click RESET once. Place another test charge at the same location. Use the VIEW SPEED bar to slow down the animation. Click PLAY. Note how the kinetic, potential, and total energies change during the motion in the box at the upper left corner. Repeat the above steps using a positive fixed charge. The electric field, at point P, of a positive charge points...
			A)	toward the charge
			B)	away from the charge
			C)	at right angles to a line from the charge to the point P
2			As you move closer to a positive point charge, the electric potential takes on...
			A)	decreasing negative values
			B)	decreasing positive values
			C)	increasing negative values
			D)	increasing positive values
3			A positive test charge in the electric field of a positive charge will move...
			A)	toward increasing electric potential
			B)	toward decreasing electric potential
			C)	along an equipotential